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Effects of intravenous morphine and lidocaine on bacterial growth

BMC Anesthesiology volume 25, Article number: 190 (2025) Cite this article

Abstract

Background

Infection prevention and control remain critical challenges in the ICU. Morphine, a frequently used opioid for postoperative pain management, may indirectly promote infections, whereas lidocaine might have protective effects. However, data regarding the direct influence of morphine and lidocaine, at concentrations within the range of plasma concentrations, on common ICU bacterial strains are lacking. This is the first study to investigate the direct effects of morphine and lidocaine at plasma concentrations corresponding to possible clinical settings, as seen in multimodal analgesia regimens, on bacterial growth using microbiological assays and transmission electron microscopy.

Methods

Morphine (1000 ng/ml, 2000 ng/ml) and lidocaine (4 µg/ml, 10 µg/ml) were placed in contact with standard strains of Escherichia coli, Pseudomonas aeruginosa and Staphylococcus aureus and tested using diffusion method, broth dilution method, and time-kill assay. Additionally, E. coli, P. aeruginosa and S. aureus were exposed to lidocaine 10 µg/ml and examined via transmission electron microscopy.

Results

Morphine and lidocaine exhibited neither stimulatory nor inhibitory effects on bacterial growth, regardless of concentration, volume, or exposure time in microbiological testing. In contrast, transmission electron microscopy revealed that lidocaine exposure altered bacterial ultrastructure, causing significant cell wall disorganization and rupture, alterations in cytoplasmic and nucleolar structure, and the appearance of “ghost cells”, indicative of cell lysis.

Conclusions

At plasma concentrations, morphine and lidocaine do not directly affect bacterial growth in vitro microbiological laboratory testing. Lidocaine on the other hand, in higher plasma concentrations, disrupts bacterial ultrastructure. Further studies are needed to investigate the significance and clinical impact of these findings.

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Background

Adequate management of intraoperative nociception/antinociception balance and postoperative pain are some of the cornerstones in anesthesia practice. Opioids are essential for moderate to severe acute pain control during the perioperative period, but, due to numerous side effects such as nausea and vomiting, postoperative ileus, urinary retention, delirium, respiratory depression, excessive sedation, recent guidelines recommend limiting their use in favor of a multimodal opioid-sparing analgesia technique, including the use of intravenous lidocaine infusions [1,2,3].

Morphine is one of the most frequently used opioid in the perioperative period due to its high potency and longer duration of action. Apart from the well-known complications and adverse reactions linked to its use, it has been shown that morphine increases susceptibility to bacterial infection by negatively influencing innate as well as adaptive immune system [4]. Moreover, studies have demonstrated a direct link between sepsis and opioids, with higher circulating endogenous morphine concentrations in septic patients, as well as a higher mortality in septic patients treated with opioids [5, 6]. Morphine, also being partially secreted by neutrophils, has the role of a signaling molecule in the host defense mechanism [5]. Furthermore, sequence similarities between morphine biosynthesis enzymes and proteins encoded by Pseudomonas aeruginosa have been found, suggesting that morphine may be synthesized by bacteria as a mechanism to increase virulence [7].

Lidocaine, on the other hand, has anti-inflammatory properties, by acting on immune cells such as polymorphonuclear granulocytes or macrophages, as well as reducing the synthesis of cytokines, free radicals and other inflammatory mediators [8,9,10,11]. Regarding the direct effect of local anesthetics on bacteria, lidocaine has a dose-dependent inhibitory effect on growth of pathogens such as Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus, Enterococcus faecalis, Acinetobacter baumannii [12,13,14,15]. In clinical settings, topical and locally/regionally administered lidocaine may exhibit its antimicrobial properties in prevention of surgical site infections, catheter associated infections, or oropharyngeal biofilm reduction [16].

While morphine may promote bacterial infection and lidocaine inhibit it, the in vitro effects of serum concentrations of morphine and lidocaine on bacterial growth have not been studied. The aim of this study is to determine whether clinically compatible plasma concentrations of morphine and lidocaine influence bacterial growth in standard strains. We selected some of the most frequently encountered strains in the ICU such as S. aureus, E. coli, P. aeruginosa. Additionally, we examined the morphological changes of these pathogens induced by lidocaine using electron microscopy.

Methods

Drugs

Commercially available solutions of morphine (Zentiva Morphine clorhidrate, 20 mg/ml) and lidocaine (Kabi Lidocaine clorhidrate, 10 mg/ml) were used in this study. Serial dilutions were prepared using sterile 0.9% NaCl solution under strict aseptic laboratory conditions. The drug concentrations used for this study are compatible with plasma concentrations range as documented in the literature: morphine in concentrations of 1000 and 2000 nanograms/mililiter and lidocaine in concentrations of 4 and 10 micrograms/mililiter [17,18,19]. The morphine concentrations used in this study are comparable to plasma levels used in previous studies reporting immunomodulatory effects of morphine. Although relatively high, we deliberately chose this concentrations to maintain methodological alignment with previous investigations in the field [17, 18].

Bacterial strains.

To evaluate the effect of morphine and lidocaine on pathogen growth, standard strains of Staphylococcus aureus ATCC29213, Escherichia coli ATCC25922 and Pseudomonas aeruginosa ATCC27853 were used. Each bacterial strain was cultured on blood agar for 24 h. Bacterial suspensions were then prepared in 0.9% NaCl and adjusted to a turbidity of 0.5 McFarland, corresponding to an approximate concentration of 1–2 × 108 CFU/ml. We chose these strains as being most frequent causes of nosocomial infections and bacterial resistance.

Laboratory techniques

Experimental testing was conducted in two distinct laboratories to replicate the results. To date there is no standard accepted technique to test for bacteria sensibility to analgesics and anesthetics. As a consequence, laboratory testing methods were derived from antibiotics sensibility testing.

Diffusion method: a 0.5 McFarland suspension of each bacterial strain was inoculated onto Mueller-Hinton agar plate (bioMérieux SA, Marcy-l’Étoile, France) using a sterile swab. Four sterile filter paper discs (Oxoid, Wade Road, Basingstoke, UK) were then applied to the plate. Each disc was pipetted with 10 µl of the prepared solutions: lidocaine at 4 µg/ml, morphine at 1000 ng/ml, morphine at 2000 ng/ml and control sterile 0.9% NaCl solution. Additionally, plates with wells containing volumes of 150 µl of morphine or lidocaine (using the same concentrations), as well as a control well with sterile 0.9% NaCl, were prepared. The Mueller-Hinton agar plates were incubated at 35 ± 1 °C in an aerobic atmosphere for 18 ± 2 h and for extended time 24 h. After incubation, the plates were examined for bacterial growth, including evaluation for any visible inhibition zones.

Diffusion method of combined lidocaine and morphine: 0.5 McFarland suspension of each bacterial strain was inoculated onto Mueller-Hinton agar plate (bioMérieux SA, Marcy-l’Étoile, France) using the streak method with a sterile swab. After inoculation, sterile wells were created in which a combination of morphine and lidocaine was added in each well: 60 µl of lidocaine 4 µg/ml + 60 µl morphine 1000 ng/ml, 60 µl of lidocaine 4 µg/ml + 60 µl morphine 2000 ng/ml. The plates were incubated for 18–24 h at 35 ± 1 °C. After incubation, the plates were examined for bacterial growth, including evaluation for any visible inhibition zones.

Broth method: tubes containing 5 ml of Mueller-Hinton broth (CA-MHB, Oxoid, Wade Road, Basingstoke, UK) were prepared with a concentration of 4 µg/ml lidocaine, 1000 ng/ml morphine, and 2000 ng/ml morphine, respectively, as well as a control tube containing a sterile 0.9% NaCl solution. All strains were tested in combination with each drug concentration and control. 25 µl of E. coli, P. aeruginosa and S. aureus 0.5 McFarland suspension were added, resulting in a final bacterial concentration of 7.5 × 105 CFU/ml in each tube. The tubes were vigorously vortexed to ensure uniform distribution of the bacterial suspension. Subsequently, 10 µl loops were used to inoculate blood agar plates from each tube. Both the tubes and the plates were incubated at 35 ± 1 °C in an aerobic atmosphere for 18 ± 2 h. To verify whether there was a reduction in the number of bacterial colonies due to incubation in the presence of lidocaine and morphine, additional blood agar plates were inoculated from the incubated tubes using a 10 µl loop. These plates were then incubated at 35 ± 1 °C in an aerobic atmosphere for 18 ± 2 h. After incubation, the plates were examined to evaluate bacterial growth.

Time-kill assay: 500 µl of 0.5 McFarland suspension of each bacterial isolate was mixed with 500 µl of lidocaine 10 µg/ml, morphine 1000 ng/ml and respectively morphine 2000 ng/ml. Subsequently, inoculations were performed using WASP analyzer (Copan, Italy) at 0, 30, 60, 120, 240 min after the solutions were in contact. Inoculation was performed using streak plate method across four quadrants, on Columbia agar + 5% sheep blood (Biomeriux and Brilliance UTI Agar (Oxioid). The plates were incubated at 37 °C 18–24 h. After the incubation period, plates were examined for bacterial growth in the four quadrants.

Transmission electron microscopy

Lidocaine 10 µg/ml, and sterile 0.9% NaCl (control) were each combined with 1.5 ml of a 2.5 McFarland suspension of S. aureus ATCC 29213, E. coli ATCC 25922 and P. aeruginosa ATCC 27853 respectively. The resulted solutions were incubated for 120–150 min. All samples were centrifuged for 15 min at 2500 g in a Jouan CR-31 centrifuge (Jouan S.A., St. Herblain, France) at room temperature. We selected this centrifugal acceleration in order to allow sedimentation of both bacilli and cocci and to avoid lysis of bacteria. The supernatant was removed and bacteria were fixed 1 h with 1.5% OsO4 (Electron Microscopy Sciences, Hatfield, PA, USA) in 0.15 M phosphate buffer, followed by dehydration with acetone 30–100%, 15 min each bath (Merck, Darmstadt, Germany), and infiltrated with an EMBED 812 epoxy resin series (Electron Microscopy Sciences, Hatfield, PA, USA) in acetone (30–90% 30 min each, and pure resin overnight). Resin polymerized for 72 h at 60 °C. Ultrathin sections cut with an ultra 45° diamond knife (DiATOME AG, Nidau, Switzerland) on a Bromma 8800 ULTRATOME III ultramicrotome (LKB, Stockholm, Sweden) were collected on 300 mesh formvar (Electron Microscopy Sciences, Hatfield, PA, USA) coated copper grids (Agar Scientific, Stansted, UK). The sections were next double contrasted 15 min with 13% uranyl acetate (Merck, Darmstadt, Germany), and 5 min with 2.8% lead citrate (Fluka, Buchs, Switzerland). Examination was performed with a JEOL JEM 100CX II transmission electron microscope (JEOL, Tokyo, Japan) operating at 80 kV, and images were recorded with a MegaView G3 camera with a Radius 2.1 software (both from EMSIS GmbH, Münster, Germany).

Results

Laboratory microbiological testing

No differences in the growth of S. aureus, E. coli, or P. aeruginosa, were observed, when adding 10 µl of lidocaine 4 µg/ml or morphine 1000 ng/ml and 2000 ng/ml respectively, in diffusion testing method as compared to control 0.9% NaCl solution. No inhibition zones were observed in any of the tested substances. Subsequently, increasing the quantity of the drug added to sterile wells up to 150 µl and extending the incubation time to 24 h had no influence on bacterial growth, nor did it result in inhibition zones.

Combining lidocaine and morphine in the same well also led to no difference in bacterial growth or inhibition zones compared to lidocaine and morphine alone or the control 0.9% NaCl solution.

Similarly, broth testing method and further incubating samples from the broth tubes on agar plates for another 18 ± 2 h did not modify pathogen growth compared to control 0.9% NaCl solution.

Time-kill assay, with extending contact time of lidocaine and morphine with the bacterial strains up to 240 min before incubation and increasing the concentration of lidocaine solution to 10 µg/ml did not result in any differences in bacterial growth. Bacterial proliferation was observed in all four quadrants, with comparable growth across all tested substances.

Transmission electron microscopy (TEM)

Staphylococcus aureus

Examination of S. aureus samples from the control group (sterile 0.9% NaCl) by TEM showed the normal morphology and ultrastructure of this Gram-positive bacterium. Thus, numerous bacteria undergoing, or that have just completed cell division were found, being separated by a complete septum, along with other non-dividing cells. The staphylococci were oval-round and contained an electron-dense, homogeneous cytoplasm within which the chromosome was visible in a lighter central region. The cell membrane was surrounded by a thick, continuous peptidoglycan layer forming the cell wall, specific for Gram-positive bacteria. (Fig. 1- TEM of Staphylococcus aureus in sterile 0.9% NaCl solution).

Fig. 1
figure 1

Transmission electron microscopy of S. aureus in sterile 0.9% NaCl. In A cocci that have completed or undergoing cell division with complete septum along with non dividing cells (top right corner). In B cocci undergoing cell division with septum present

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In 10 µg/ml lidocaine group, some staphylococci preserved their normal general aspect. However, the large majority of bacteria in this group lost their preexisting wall in extensive areas, in the regions in contact with the environment, resulting in the outflow of cytoplasm outside the cell. At high magnifications the discontinuity of the wall was observed in dividing cells especially in the thinner lateral regions distant from the incomplete septa. The newly formed cell wall remained relatively intact, even in cells where the plasma membrane was disrupted or removed. In addition, cocci showed rarefied, heterogeneous cytoplasm, filled with dense granules, resulting in a granular cytoplasmic pattern (Fig. 2- TEM of S. aureus in 10 µg/ml lidocaine).

Fig. 2
figure 2

Transmission electron microscopy of S. aureus in 10 µg/ml lidocaine. In A a minority of cocci maintaining their normal appearance, alongside a majority of cocci with disrupted cell walls as well as a granular pattern. In the top right corner, dividing daughter cells with intact new cell wall but with disrupted former membranes are shown. In B, a magnified view of S. aureus is presented, displaying disrupted lateral membranes and dense granules in the cytoplasm

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Escherichia coli

Examination of E. coli samples in the control group (sterile 0.9% NaCl solution) showed normal morphology and ultrastructure. No bacilli with flagella were noticed in our samples, most likely due to the flagella being detached during centrifugation and discarded with the supernatant. The cytoplasm of E. coli cells appeared electron-dense, with a uniform granular pattern. Electron-lucent areas, corresponding to the chromosome’s presence and location, were also visible, distributed randomly within the cells. These bacteria were surrounded by two distinct membranes: the inner cytoplasmic membrane, relatively smooth and uniform, and the undulating outer membrane. Between the two membranes, periplasm contained a thin peptidoglycan layer (Fig. 3- TEM of E. coli in sterile 0.9% NaCl).

Fig. 3
figure 3

Transmission electron microscopy of E. coli in sterile 0.9% NaCl. A and B display rod-shaped bacilli with granular cytoplasm and electron-lucent areas corresponding to the chromosomes. The membrane consists of two distinct layers, with a thin peptidoglycan layer situated in between

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Incubation of E. coli with lidocaine 10 µg/ml primarily resulted in cytoplasmic degeneration. Many bacterial cells presented electron-lucent regions. Another frequent structural alteration was the overall tendency of rarefaction of the entire cytoplasm. Additionally, almost all examined cells showed regions of clumped cytoplasm, appearing as large, homogeneous grey spots. Some bacteria displayed extremely rarefied cytoplasm, transforming into “ghost cells”. This transformation affected both bacteria in the early stages of cell division as well as those that had completed division. Ultimately, incubating E. coli with lidocaine led to irregularly shaped bacteria, although their membrane appeared intact (Fig. 4- TEM of E. coli in 10 µg/ml lidocaine).

Fig. 4
figure 4

Transmission electron microscopy of E. coli in 10 µg/ml lidocaine. A electron-lucent regions around the chromosome as well as rarefied cytoplasm with clumped regions (top right corner). In B irregular shaped E coli with intact membranes, as well as clumped and rarefied cytoplasm (bottom left corner), and a “ghost cell” in the center

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Pseudomonas aeruginosa

Similarly to the other strains, examination of P. aeruginosa samples from the control group treated with sterile 0.9% NaCl solution showed typical morphology and ultrastructure. Bacteria were rod-shaped, in different stages of cell division. No flagella were detected, likely due to the detachment during centrifugation and subsequent removal with the supernatant. The cytoplasm was electron-dense, with a uniform granular pattern, apparently denser than that of E. coli. Electron-lucent areas, corresponding to the location of the chromosome, occupied a large proportion of the intracellular space. Two distinct membranes were visible as parallel, undulating lines, with a thicker outer lipopolysaccharide membrane. Between the two membranes, a peptidoglycan layer could be seen in the periplasm (Fig. 5- TEM of P. aeruginosa in sterile 0.9% NaCl solution).

Fig. 5
figure 5

Transmission electron microscopy of P. aeruginosa in sterile 0.9% NaCl. A and B display rod shaped bacteria, with electron-dense, granular cytoplasm covered by a peptidoglycan layer in between two parallel membranes

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In the 10 µg/ml lidocaine group, the most notable ultrastructural change of P. aeruginosa was a significant expansion of the electron light region of the nucleoid, with only a thin layer of dense, granular cytoplasm separating it from the cell wall. Another cellular alteration was the presence of a relatively high number of “ghost cells”. These cells appeared to have intact membranes but were either entirely devoid of cytoplasm or contained very little and/or clumped cytoplasm. These “ghost cells” had irregular contour in almost all cases (Fig. 6- TEM of P. aeruginosa in 10 µg/ml lidocaine).

Fig. 6
figure 6

Transmission electron microscopy of P. aeruginosa in 10 µg/ml lidocaine. A and B show bacteria with expansion of the electron light region of the nucleoid. Numerous “ghost cells” are represented, devoid or cytoplasm or with little, clumped cytoplasm remaining (A bottom and top right corner)

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Discussion

Sepsis continues to be a growing and critical healthcare challenge, significantly contributing to rising medical costs and high mortality rates. It is responsible for the death of approximately one in every three to six individuals affected by this condition [20]. The incidence of infections in both medical and surgical Intensive Care Units (ICU) is over 50%, highlighting the critical need to reduce risk factors and implement strategies to prevent the onset of infections leading to sepsis and septic shock [21].

Opioids are commonly administered in both surgical and medical ICUs due to their role in managing acute and severe pain. The advantage of high potency is counterbalanced by the multitude of adverse reactions, which can hinder the patient’s rapid recovery. Alongside the commonly acknowledged negative side effects, in vivo, in vitro, and clinical studies have demonstrated that opioids may increase susceptibility to infection by impairing both humoral and cell-mediated components of the innate and adaptive immune system [4]. Therefore, recent guidelines such as Enhanced Recovery After Surgery (ERAS) and Procedure specific postoperative pain management (Prospect) advocate for a reduction in opioid use in favor of a multimodal analgesia approach [2, 3, 22]. Within this multimodal approach, local anesthetics play an important role in the context of regional techniques. More recently, intravenous lidocaine gained popularity due to its analgesic and anti-inflammatory properties [2].

To our knowledge, this study is the first to assess the potential direct impact of different concentrations of lidocaine and morphine, compatible with clinical concentrations, on commonly encountered gram positive as well as gram negative bacteria in the ICU. The objective was to determine whether, in addition to the known immunosuppressive effects of morphine that promote bacterial growth and the antiinflammatory effects of lidocaine, these drugs directly influence bacterial proliferation.

In our microbiological tests, morphine exhibited neither inhibitory nor stimulatory effects on the bacterial strains, regardless of the concentration, volume, or incubation time. Our finding are consistent with a study by Rosenberg, where morphine at concentrations of 0.2 mg/ml and 2 mg/ml showed no effect on any of the 10 microorganisms tested, including E. coli, P. aeruginosa, and S. aureus. Notably, the concentrations used in Rosenberg’s study were significantly higher compared to those used in our study, corresponding to regional analgesia infiltrations rather than plasma concentrations. Nevertheless, no impact on bacterial growth was demonstrated. However, it is important to note that this conclusion was based on a single laboratory testing method [23].

It could be speculated that the primary mechanism through which morphine may promote infection is an indirect one, exerting a negative influence on the immune system. The interaction between exogenous and endogenous opioids and the immune system is complex, yet it appears to be closely linked to the mu opioid receptor (MOR) [24]. Morphine not only decreases bone marrow macrophage colony formation but also inhibits immune cells recruitment and apoptosis rate, resulting in phagocytosis suppression [4, 24]. Moreover, morphine suppresses neutrophil migration and inhibits mast cell activation, thereby further impairing the function of the innate immune system [4, 24]. Morphine also alters T and B cell function, both of which express mu receptors [24]. It has been shown that morphine treatment increases susceptibility to bacteria such as S. aureus, P. aeruginosa, A. baumannii, S. pneumoniae, K. pneumoniae, and Citrobacter rodentium (a murine model for E. coli) [6, 18, 24,25,26,27]. This increased susceptibility is attributed to morphine’s immunosuppressive effects, rather than any direct impact of morphine on the bacteria themselves, as confirmed by our study.

The antibacterial properties of local anesthetics, including lidocaine, have been reported for many years [16]. Historically, lidocaine’s primary indication has been for local or regional analgesia or anesthesia, leading to numerous studies that have demonstrated its antibacterial effects. These effects have been observed following intravitreal injections, in the prophylaxis of surgical and nosocomial wound infections, in the prevention of catheter-associated infections, in dentistry and oral surgery through the reduction of biofilm formation, as well as in pathogens isolated from spinal or epidural abscesses, and in respiratory pathogens identified during bronchoscopy [16]. Given that the concentrations used for these purposes exceed the plasma levels achieved by intravenous infusion, we aimed to determine whether the antibacterial properties of lidocaine are preserved at the plasma concentrations typically reached during systemic administration.

In 2019, Kesici demonstrated the antibacterial effect of 2% lidocaine on P. aeruginosa, S. aureus and E. coli by impregnating sterile discs with 20 µl of the anesthetic [14]. However, in contrast with Kesici’s study, in our study, lidocaine at a concentration of 4 µg/ml and 10 µg/ml showed no significant difference in inhibition zones compared to control. The different results are most likely due to the different concentrations and method used. To test whether the antimicrobial efficacy of local anesthetics may be both concentration- and volume-dependent, we conducted two separate approaches: we increased the lidocaine concentration to 10 µg/ml, corresponding to the toxic plasma threshold, with a volume of 500 µl in the time-kill assay, and we also increased the volume of the 4 µg/ml lidocaine solution up to 150 µl. In both cases, no impact on bacterial growth was observed.

Prior studies have demonstrated that lidocaine has time dependent antibacterial capacity [13]. In our study we also progressively increased exposure time of bacteria to lidocaine before incubation for up to 4 h, and also incubated bacteria with lidocaine for 24 h on broth before inoculation, which yielded no significant effect on bacterial growth. Although bactericidal and inhibitory concentrations of lidocaine against E. Coli, P. aeruginosa and S. aureus vary across different studies throughout literature, with some studies even reporting resistance of Staphylococcus and P. aeruginosa species, in all studies, tested concentrations exceeded 4–10 µg/ml safety plasma levels [12,13,14, 28]. As opposed to most of the findings published so far, our study demonstrated that lidocaine in concentrations of 4 µg/ml to 10 µg/ml does not exhibit antibacterial effects, regardless of the volume, duration of exposure, incubation conditions or laboratory method used, in microbiological testing. Potential explanations for our results may consist in the different method and concentrations used for testing.

However, in our study, even though lidocaine at plasma concentrations did not exhibit antibacterial effects in conventional microbiological testing, transmission electron microscopy showed notable ultrastructural modifications. Bacteria exposed to 10 µg/ml lidocaine exhibited significant cell wall disorganization, with some instances of rupture. Additionally, alterations in cytoplasmic architecture and nucleoid structure were observed when compared to untreated controls. These findings suggest a potential altering effect of lidocaine on the tested strains. The varying responses of the bacteria suggest that different strains may exhibit varying degrees of susceptibility to lidocaine.

S. aureus presented discontinuity in the cell wall, leading to cytoplasmic outflow, features indicating perimortem modifications of the bacteria [29, 30]. Moreover, the cytoplasm appeared structureless, with clumps of different electron density, similar to those observed in strains treated with different antibiotics and bactericidal compounds [31, 32]. Cell lysis is not a prerequisite for S. aureus cell death, as certain antibacterial mechanisms, such as those induced by ciprofloxacin, can occur without lysis [29]. Consequently, no “ghost cells” were observed in our experiment.

In the case of E. coli, the most prominent alterations were observed in the cytoplasm, which exhibited a granular pattern or clumps similar to those described in S. aureus. However, in E. coli, vacuole-like structures also emerged, a feature commonly seen following antibiotic treatment [33]. Moreover, the irregularly shaped E. coli observed following exposure to lidocaine mirrors the morphological changes reported when bacteria are exposed to membrane-targeting antibiotics, most likely indicating alterations in the peptidoglycan layer, leading to the loss of characteristic rod shape [33].

Although antibiotics do not directly target the nucleoid of P. aeruginosa, as their primary mechanism of action involves inhibiting ribosomal protein synthesis and disrupting the cell wall, in our study, lidocaine induced alterations of the normal structure and dimensions of the nucleoid, though the significance of these changes remains unclear [34]. These modifications may be related to disruptions in DNA replication and transcription processes within the nucleoid [29].

The most striking ultrastructural change caused by lidocaine in E. coli and P. aeruginosa was the appearance of some “ghost cells”, characterized by a near-complete absence of cytoplasm, indicating a perimortem state consistent with bacterial lysis [29]. However, in the absence of functional viability assays, it can not be definitively concluded that these structural alterations represent complete loss of viability.

Morphine solution contained monocalcium disodium EDTA, a preservative with antioxidant and metal-ion chelating properties. This compound is related to both disodium EDTA and EDTA, which have been associated with antimicrobial-enhancing properties [35]. However, we did not find any literature evidence of antimicrobial properties in monocalcium disodium EDTA, nor did it influence our results, as morphine exhibited no antibacterial activity. Lidocaine, on the other hand, contained only hydrochloric acid and sodium hydroxide for pH stabilization, with no additional preservatives.

Our study has a few limitations. First, lidocaine and morphine solutions were not sterilized before incubation with bacteria. However, all procedures were conducted under strict aseptic, sterile conditions and we confirmed the absence of bacterial contamination by testing the prepared dilutions. Another limitation is that we were unable to count the exact number of CFU/ml, as we did not use suspension dilution method or PCR testing. In addition, we did not apply statistical analysis to the microbiological results, as the methods used did not allow precise quantification of bacterial growth. As a result, minor variations in bacterial proliferation may have gone undetected. Moreover, we did not determine Minimum Inhibitory Concentration (MIC) or Minimum Bactericidal Concentration (MBC) as our study focused on direct effects of relevant drug plasma concentrations on bacteria growth and ultrastructure.

For transmission electron microscopy, since lidocaine did not exhibit antibacterial effects in conventional microbiological testing, we proceeded to assess only the higher concentration of 10 µg/ml. This plasma concentration can be associated with significant adverse reactions and is usually above that reached in clinical practice. It is possible that for lower concentrations these effects would have not been the same. Another limitation is that we did not analyze the bacterial appearance using transmission electron microscopy at various exposure times to observe comparatively any changes induced by lidocaine on the bacteria, taking into consideration that in clinical practice, intravenous lidocaine infusions may be used for up to 48 h. Among lidocaine treated bacteria a number of cells appeared almost unaffected, while others displayed various intermediate ultrastructural changes. These cells were not selected for publication, but their presence highlights bacterial heterogeneity.

Conclusion

In conclusion, this is the first experimental study to investigate the effects of lidocaine and morphine in concentrations corresponding to plasma concentrations on bacterial growth, using both microbiological and transmission electron microscopy. We did not observe any direct effects of morphine on bacterial multiplication. In our study, lidocaine in high concentrations, above those regularly used in clinical practice, induced distinct ultrastructural alterations in the tested bacterial strains, including morphological changes consistent with perimortem injury. However, given that lidocaine had no effect on bacterial growth in conventional microbiological assays, the functional significance of these structural modifications remains uncertain. Further studies are needed to elucidate whether these changes reflect early stages of bacterial cell death or represent sublethal stress responses without direct impact on bacterial viability, to assess the reproductibility of these effects at lidocaine concentrations of 4–6 µg/ml and to determine their clinical relevance.

Data availability

No datasets were generated or analysed during the current study.

Abbreviations

TEM:

Transmission electron microscopy

PCR:

polymerase chain reaction

CFU:

Colony forming units

References

  1. Shim H, Gan TJ. Side effect profiles of different opioids in the perioperative setting: are they different and can we reduce them? Br J Anaesth. 2019;123(3):266–8. https://doiorg.publicaciones.saludcastillayleon.es/10.1016/j.bja.2019.06.009.

    Article  PubMed  Google Scholar 

  2. Melloul E, Lassen K, Roulin D, Grass F, Perinel J, Adham M, Wellge EB, Kunzler F, Besselink MG, Asbun H, Scott MJ, Dejong CHC, Vrochides D, Aloia T, Izbicki JR, Demartines N. Guidelines for perioperative care for pancreatoduodenectomy: enhanced recovery after surgery (ERAS) recommendations 2019. World J Surg. 2020;44(7):2056–84. https://doiorg.publicaciones.saludcastillayleon.es/10.1007/s00268-020-05462-w.

    Article  PubMed  Google Scholar 

  3. Feldheiser A, Aziz O, Baldini G, Cox BP, Fearon KC, Feldman LS, Gan TJ, Kennedy RH, Ljungqvist O, Lobo DN, Miller T, Radtke FF, Ruiz Garces T, Schricker T, Scott MJ, Thacker JK, Ytrebø LM, Carli F. Enhanced recovery after surgery (ERAS) for Gastrointestinal surgery, part 2: consensus statement for anaesthesia practice. Acta Anaesthesiol Scand. 2016;60(3):289–334. https://doiorg.publicaciones.saludcastillayleon.es/10.1111/aas.12651.

    Article  CAS  PubMed  Google Scholar 

  4. Plein LM, Rittner HL. Opioids and the immune system - friend or foe. Br J Pharmacol. 2018;175(14):2717–25. https://doiorg.publicaciones.saludcastillayleon.es/10.1111/bph.13750.

    Article  CAS  PubMed  Google Scholar 

  5. Glattard E, Welters ID, Lavaux T, Muller AH, Laux A, Zhang D, Schmidt AR, Delalande F, Laventie BJ, Dirrig-Grosch S, Colin DA, Van Dorsselaer A, Aunis D, Metz-Boutigue MH, Schneider F, Goumon Y. Endogenous morphine levels are increased in sepsis: a partial implication of neutrophils. PLoS ONE. 2010;5(1):e8791. https://doiorg.publicaciones.saludcastillayleon.es/10.1371/journal.pone.0008791.

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  6. Zhang R, Meng J, Lian Q, Chen X, Bauman B, Chu H, Segura B, Roy S. Prescription opioids are associated with higher mortality in patients diagnosed with sepsis: A retrospective cohort study using electronic health records. PLoS ONE. 2018;13(1):e0190362. https://doiorg.publicaciones.saludcastillayleon.es/10.1371/journal.pone.0190362.

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  7. Zhan SH, French L. Sequence similarity searches for morphine biosynthesis enzymes in bacteria yield putative targets for Understanding associations between infection and opiate administration. J Med Microbiol. 2019;68(6):952–6. https://doiorg.publicaciones.saludcastillayleon.es/10.1099/jmm.0.001001.

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  8. Hollmann MW, Durieux ME. Local anesthetics and the inflammatory response: a new therapeutic indication? Anesthesiology. 2000;93(3):858–75. https://doiorg.publicaciones.saludcastillayleon.es/10.1097/00000542-200009000-00038.

    Article  CAS  PubMed  Google Scholar 

  9. Karnina R, Arif SK, Hatta M, Bukhari A. Molecular mechanisms of Lidocaine. Ann Med Surg (Lond). 2021;69:102733. https://doiorg.publicaciones.saludcastillayleon.es/10.1016/j.amsu.2021.102733.

    Article  PubMed  Google Scholar 

  10. Alexa AL, Sargarovschi S, Ionescu D. Neutrophils and anesthetic drugs: implications in Onco-Anesthesia. Int J Mol Sci. 2024;25(7):4033. https://doiorg.publicaciones.saludcastillayleon.es/10.3390/ijms25074033.

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  11. Galoș EV, Tat TF, Popa R, Efrimescu CI, Finnerty D, Buggy DJ, Ionescu DC, Mihu CM. Neutrophil extracellular trapping and angiogenesis biomarkers after intravenous or inhalation anaesthesia with or without intravenous Lidocaine for breast cancer surgery: a prospective, randomised trial. Br J Anaesth. 2020;125(5):712–21. https://doiorg.publicaciones.saludcastillayleon.es/10.1016/j.bja.2020.05.003.

    Article  CAS  PubMed  Google Scholar 

  12. Parr AM, Zoutman DE, Davidson JS. Antimicrobial activity of Lidocaine against bacteria associated with nosocomial wound infection. Ann Plast Surg. 1999;43(3):239–45. https://doiorg.publicaciones.saludcastillayleon.es/10.1097/00000637-199909000-00003.

    Article  CAS  PubMed  Google Scholar 

  13. Aydin ON, Eyigor M, Aydin N. Antimicrobial activity of ropivacaine and other local anaesthetics. Eur J Anaesthesiol. 2001;18(10):687–94. https://doiorg.publicaciones.saludcastillayleon.es/10.1046/j.1365-2346.2001.00900.x.

    Article  CAS  PubMed  Google Scholar 

  14. Kesici U, Demirci M, Kesici S. Antimicrobial effects of local anaesthetics. Int Wound J. 2019;16(4):1029–33. https://doiorg.publicaciones.saludcastillayleon.es/10.1111/iwj.13153.

    Article  PubMed  PubMed Central  Google Scholar 

  15. Nazarchuk O, Dmyrtriiev D, Babina Y, Faustova M, Burkot V. Research of the activity of local anesthetics and antiseptics regarding clinical isolates of Acinetobacter baumannii as pathogens of postoperative infectious complications. Acta Biomed. 2022;93(1):e2022003. https://doiorg.publicaciones.saludcastillayleon.es/10.23750/abm.v93i1.11842.

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  16. Razavi BM, Fazly Bazzaz BS. A review and new insights to antimicrobial action of local anesthetics. Eur J Clin Microbiol Infect Dis. 2019;38(6):991–1002. https://doiorg.publicaciones.saludcastillayleon.es/10.1007/s10096-018-03460-4.

    Article  CAS  PubMed  Google Scholar 

  17. Meng J, Banerjee S, Li D, Sindberg GM, Wang F, Ma J, Roy S. Opioid exacerbation of Gram-positive sepsis, induced by gut microbial modulation, is rescued by IL-17A neutralization. Sci Rep. 2015;5:10918. https://doiorg.publicaciones.saludcastillayleon.es/10.1038/srep10918.

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  18. Breslow JM, Monroy MA, Daly JM, Meissler JJ, Gaughan J, Adler MW, Eisenstein TK. Morphine, but not trauma, sensitizes to systemic Acinetobacter baumannii infection. J Neuroimmune Pharmacol. 2011;6(4):551–65. https://doiorg.publicaciones.saludcastillayleon.es/10.1007/s11481-011-9303-6.

    Article  PubMed  PubMed Central  Google Scholar 

  19. Greenwood E, Nimmo S, Paterson H, Homer N, Foo I. Intravenous Lidocaine infusion as a component of multimodal analgesia for colorectal surgery-measurement of plasma levels. Perioper Med (Lond). 2019;8:1. https://doiorg.publicaciones.saludcastillayleon.es/10.1186/s13741-019-0112-4.

    Article  CAS  PubMed  Google Scholar 

  20. Evans L, Rhodes A, Alhazzani W, Antonelli M, Coopersmith CM, French C, Machado FR, Mcintyre L, Ostermann M, Prescott HC, Schorr C, Simpson S, Wiersinga WJ, Alshamsi F, Angus DC, Arabi Y, Azevedo L, Beale R, Beilman G, Belley-Cote E, Burry L, Cecconi M, Centofanti J, Coz Yataco A, De Waele J, Dellinger RP, Doi K, Du B, Estenssoro E, Ferrer R, Gomersall C, Hodgson C, Møller MH, Iwashyna T, Jacob S, Kleinpell R, Klompas M, Koh Y, Kumar A, Kwizera A, Lobo S, Masur H, McGloughlin S, Mehta S, Mehta Y, Mer M, Nunnally M, Oczkowski S, Osborn T, Papathanassoglou E, Perner A, Puskarich M, Roberts J, Schweickert W, Seckel M, Sevransky J, Sprung CL, Welte T, Zimmerman J, Levy M. Surviving sepsis campaign: international guidelines for management of sepsis and septic shock 2021. Intensive Care Med. 2021;47(11):1181–247. https://doiorg.publicaciones.saludcastillayleon.es/10.1007/s00134-021-06506-y.

    Article  PubMed  PubMed Central  Google Scholar 

  21. Vincent JL, Sakr Y, Singer M, Martin-Loeches I, Machado FR, Marshall JC, Finfer S, Pelosi P, Brazzi L, Aditianingsih D, Timsit JF, Du B, Wittebole X, Máca J, Kannan S, Gorordo-Delsol LA, De Waele JJ, Mehta Y, Bonten MJM, Khanna AK, Kollef M, Human M, Angus DC. EPIC III investigators. Prevalence and outcomes of infection among patients in intensive care units in 2017. JAMA. 2020;323(15):1478–87. https://doiorg.publicaciones.saludcastillayleon.es/10.1001/jama.2020.2717.

    Article  PubMed  PubMed Central  Google Scholar 

  22. Uten T, Chesnais M, van de Velde M, Raeder J, Beloeil H, PROSPECT Working group of the European Society of Regional Anaesthesia Pain therapy (ESRA). Pain management after open colorectal surgery: an update of the systematic review and procedure-specific postoperative pain management (PROSPECT) recommendations. Eur J Anaesthesiol. 2024;41(5):363–6. https://doiorg.publicaciones.saludcastillayleon.es/10.1097/EJA.0000000000001978.

    Article  PubMed  Google Scholar 

  23. Rosenberg PH, Renkonen OV. Antimicrobial activity of bupivacaine and morphine. Anesthesiology. 1985;62(2):178–9. https://doiorg.publicaciones.saludcastillayleon.es/10.1097/00000542-198502000-00015.

    Article  CAS  PubMed  Google Scholar 

  24. Eisenstein TK. The role of opioid receptors in immune system function. Front Immunol. 2019;10:2904. https://doiorg.publicaciones.saludcastillayleon.es/10.3389/fimmu.2019.02904.

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  25. Wang F, Meng J, Zhang L, Roy S. Opioid use potentiates the virulence of hospital-acquired infection, increases systemic bacterial dissemination and exacerbates gut dysbiosis in a murine model of Citrobacter rodentium infection. Gut Microbes. 2020;11(2):172–90. https://doiorg.publicaciones.saludcastillayleon.es/10.1080/19490976.2019.1629237.

    Article  CAS  PubMed  Google Scholar 

  26. Wang J, Barke RA, Charboneau R, Roy S. Morphine impairs host innate immune response and increases susceptibility to Streptococcus pneumoniae lung infection. J Immunol. 2005;174(1):426–34. https://doiorg.publicaciones.saludcastillayleon.es/10.4049/jimmunol.

    Article  CAS  PubMed  Google Scholar 

  27. Babrowski T, Holbrook C, Moss J, Gottlieb L, Valuckaite V, Zaborin A, Poroyko V, Liu DC, Zaborina O, Alverdy JC. Pseudomonas aeruginosa virulence expression is directly activated by morphine and is capable of causing lethal gut-derived sepsis in mice during chronic morphine administration. Ann Surg. 2012;255(2):386–93. https://doiorg.publicaciones.saludcastillayleon.es/10.1097/SLA.0b013e3182331870.

    Article  PubMed  Google Scholar 

  28. Barreto Bellusci H, Gervasoni LF, Peixoto IC, De Oliveira LB, de Oliveira Vieira KC, Toledo ACCG, de Oliveira CBS, Mareco EA, Naga RM, Cataneli VP, Nai GA, Winkelströter LK. Local anesthetics as a tool for Staphylococcus spp. Control: a systematic review. Braz J Microbiol. 2024;55(2):1427–35. https://doiorg.publicaciones.saludcastillayleon.es/10.1007/s42770-024-01285-2.

    Article  PubMed  PubMed Central  Google Scholar 

  29. Cushnie TP, O’Driscoll NH, Lamb AJ. Morphological and ultrastructural changes in bacterial cells as an indicator of antibacterial mechanism of action. Cell Mol Life Sci. 2016;73(23):4471–92. https://doiorg.publicaciones.saludcastillayleon.es/10.1007/s00018-016-2302-2.

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  30. Liu S, She P, Li Z, Li Y, Yang Y, Li L, Zhou L, Wu Y. Insights into the antimicrobial effects of ceritinib against Staphylococcus aureus in vitro and in vivo by cell membrane disruption. AMB Express. 2022;12(1):150. https://doiorg.publicaciones.saludcastillayleon.es/10.1186/s13568-022-01492-w.

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  31. Grigor’eva A, Bardasheva A, Tupitsyna A, Amirkhanov N, Tikunova N, Pyshnyi D, Ryabchikova E. Changes in the ultrastructure of Staphylococcus aureus treated with cationic peptides and chlorhexidine. Microorganisms. 2020;8(12):1991. https://doiorg.publicaciones.saludcastillayleon.es/10.3390/microorganisms8121991.

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  32. Grigor’eva AE, Bardasheva AV, Ryabova ES, Tupitsyna AV, Zadvornykh DA, Koroleva LS, Silnikov VN, Tikunova NV, Ryabchikova EI. Changes in the ultrastructure of Staphylococcus aureus cells make it possible to identify and analyze the injuring effects of Ciprofloxacin, polycationic amphiphile and their hybrid. Microorganisms. 2023;11(9):2192. https://doiorg.publicaciones.saludcastillayleon.es/10.3390/microorganisms11092192.

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  33. Muhamad Hendri NA, Nor Amdan NA, Dounis SO, Sulaiman Najib N, Louis SR. Ultrastructural and morphological studies on variables affecting Escherichia coli with selected commercial antibiotics. Cell Surf. 2024;11:100120. https://doiorg.publicaciones.saludcastillayleon.es/10.1016/j.tcsw.2024.100120.

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  34. Wood SJ, Kuzel TM, Shafikhani SH. Pseudomonas aeruginosa: infections, animal modeling, and therapeutics. Cells. 2023;12(1):199. https://doiorg.publicaciones.saludcastillayleon.es/10.3390/cells12010199.

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  35. Chaudhuri S, Gupta S. (2023). Effect of addition of disodium EDTA to ceftriaxone and sulbactam on the susceptibility of gram-negative pathogens. International Journal of Research in Medical Sciences. 2023;11(4):1175–1179. https://doiorg.publicaciones.saludcastillayleon.es/10.18203/2320-6012.ijrms20230857

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Authors and Affiliations

  1. 1st Department of Anesthesia and Intensive Care, Iuliu Hatieganu University of Medicine and Pharmacy, 8 Victor Babes Street, Cluj-Napoca, CJ, 400012, Romania

    Cristiana Iulia Osoian & Daniela Ionescu

  2. Research Association in Anesthesia and Intensive Care (ACATI), Cluj-Napoca, CJ, Romania

    Cristiana Iulia Osoian & Daniela Ionescu

  3. Department of Microbiology, Iuliu Hatieganu University of Medicine and Pharmacy, 8 Victor Babes Street, Cluj-Napoca, CJ, 400012, Romania

    Stanca Lucia Pandrea & Luminita Matros

  4. Regional Institute of Gastroenterology and Hepatology “Prof. O. Fodor”, 19-21 Croitorilor Street, Cluj-Napoca, CJ, 400394, Romania

    Stanca Lucia Pandrea

  5. Clinical Hospital of Infectious Diseases, 23 Iuliu Moldovan Street, Cluj-Napoca, CJ, 400003, Romania

    Mirela Flonta

  6. Department of Cell and Molecular Biology, Iuliu Hatieganu University of Medicine and Pharmacy, 8 Victor Babes Street, Cluj-Napoca, CJ, 400012, Romania

    Adrian Florea

  7. Outcome Research Consortium, Cleveland, OH, USA

    Daniela Ionescu

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  1. Cristiana Iulia Osoian
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  4. Adrian Florea
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Contributions

C.I.O. conceived the study, contributed in the design of the study, analysed data and wrote the manuscript. M. F. and L.M. were responsible with microbiological testing. A. F. was responsible with TEM testing. L.S.P. helped conceive the study and was responsible with microbiological testing. D. I. contributed in conceiving the study and manuscript preparation. All authors have given approval of the version to be published.

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Correspondence to Stanca Lucia Pandrea.

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Osoian, C.I., Pandrea, S.L., Flonta, M. et al. Effects of intravenous morphine and lidocaine on bacterial growth. BMC Anesthesiol 25, 190 (2025). https://doiorg.publicaciones.saludcastillayleon.es/10.1186/s12871-025-03070-6

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BMC Anesthesiology

ISSN: 1471-2253

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