Effect of pH on in vitro antimicrobial susceptibility of the Bacteroides fragilis group

Bacteria as sensors: Real-time NMR analysis of extracellular metabolites detects sub-lethal amounts of bactericidal molecules released from functionalized materials

BACKGROUND

Cells exposed to stress factors experience time-dependent variations of metabolite concentration, acting as reliable sensors of the effective concentration of drugs in solution. NMR can detect and quantify changes in metabolite concentration, thus providing an indirect estimate of drug concentration. The quantification of bactericidal molecules released from antimicrobial-treated biomedical materials is crucial to determine their biocompatibility and the potential onset of drug resistance.

METHODS

Real-time NMR measurements of extracellular metabolites produced by bacteria grown in the presence of known concentrations of an antibacterial molecule (irgasan) are employed to quantify the bactericidal molecule released from antimicrobial-treated biomedical devices. Viability tests assess their activity against E. coli and S. aureus planktonic and sessile cells. AFM and contact angle measurements assisted in the determination of the mechanism of antibacterial action.

RESULTS

NMR-derived concentration kinetics of metabolites produced by bacteria grown in contact with functionalized materials allows for indirectly evaluating the effective concentration of toxic substances released from the device, lowering the detection limit to the nanomolar range. NMR, AFM and contact angle measurements support a surface-killing mechanism of action against bacteria.

CONCLUSIONS

The NMR based approach provides a reliable tool to estimate bactericidal molecule release from antimicrobial materials.

GENERAL SIGNIFICANCE

The novelty of the proposed NMR-based strategy is that it i) exploits bacteria as sensors of the presence of bactericidal molecules in solution; ii) is independent of the chemo-physical properties of the analyte; iii) establishes the detection limit to nanomolar concentrations.

pH variation in medical implant biofilms: Causes, measurements, and its implications for antibiotic resistance

The advent of implanted medical devices has greatly improved the quality of life and increased longevity. However, infection remains a significant risk because bacteria can colonize device surfaces and form biofilms that are resistant to antibiotics and the host's immune system. Several factors contribute to this resistance, including heterogeneous biochemical and pH microenvironments that can affect bacterial growth and interfere with antibiotic biochemistry; dormant regions in the biofilm with low oxygen, pH, and metabolites; slow bacterial growth and division; and poor antibody penetration through the biofilm, which may also be regions with poor acid product clearance. Measuring pH in biofilms is thus key to understanding their biochemistry and offers potential routes to detect and treat latent infections. This review covers the causes of biofilm pH changes and simulations, general findings of metabolite-dependent pH gradients, methods for measuring pH in biofilms, effects of pH on biofilms, and pH-targeted antimicrobial-based approaches.

Application of pharmacokinetic/pharmacodynamic concepts to the development of treatment regimens for sporadic canine urinary tract infections: Challenges and paths forward

Antimicrobial efficacy can be predicted based on infection site exposure to the antimicrobial agent relative to the in vitro susceptibility of the pathogen to that agent. When infections occur in soft tissues (e.g., muscle, blood, and ligaments), exposure at the infection site is generally assumed to reflect an equilibrium between the unbound concentrations in plasma and that in the interstitial fluids. In contrast, for sporadic urinary tract infections (UTIs) in dogs and uncomplicated UTIs in humans, the primary site of infection is the bladder wall. Infection develops when bacteria invade the host bladder urothelium (specifically, the umbrella cells that form the urine-contacting layer of the stratified uroepithelium) within which these bacteria can avoid exposure to host defenses and antimicrobial agents. Traditionally, pathogen susceptibility has been estimated using standardized in vitro tests that measure the minimal concentration that will inhibit pathogen growth (MIC). When using exposure-response relationships during drug development to explore dose optimization, these relationships can either be based upon an assessment of a correlation between clinical outcome, drug exposure at the infection site, and pathogen MIC, or upon benchmark exposure-response relationships (i.e., pharmacokinetic/pharmacodynamic indices) typically used for the various drug classes. When using the latter approach, it is essential that the unbound concentrations at the infection site be considered relative to the MIC within the biological matrix to which the pathogen will be exposed. For soft tissue infections, this typically is the unbound plasma concentrations versus MICs determined in standardized media such as cation-adjusted Mueller Hinton broth, which is how many indices were originally established. However, for UTIs, it is the unbound drug concentrations within the urine versus the MICs in the actual urine biophase that needs to be considered. The importance of these relationships and how they are influenced by drug resistance, resilience, and inoculum are discussed in this review using fluoroquinolones and beta-lactams as examples.

In vitro antibacterial activity of nimbolide against Helicobacter pylori

ETHNOPHARMACOLOGICAL RELEVANCE

Nimbolide is one of hundreds of phytochemicals that have been identified within the neem tree (Azadirachta indica A. Juss). As an evergreen tree native to the Indian subcontinent, components of the neem tree have been used for millennia in traditional medicine to treat dental, gastrointestinal, urinary tract, and blood-related ailments, ulcers, headaches, heartburn, and diabetes. In modern times, natural oils and extracts from the neem tree have been found to have activities against a variety of microorganisms, including human pathogens.

AIM OF THE STUDY

Helicobacter pylori, a prevalent gastric pathogen, shows increasing levels of antibiotic resistance. Thus, there is an increasing demand for novel therapeutics to treat chronic infections. The in vitro activity of neem oil extract against H. pylori was previously characterized and found to be bactericidal. Given the numerous phytochemicals found in neem oil extract, the present study was designed to define and characterize specific compounds showing bactericidal activity against H. pylori.

MATERIALS AND METHODS

Azadirachtin, gedunin, and nimbolide, which are all common in neem extracts, were tested for antimicrobial activity; the minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) were determined for nine strains of H. pylori. The specific properties of nimbolide were further characterized against H. pylori strain G27. Bactericidal kinetics, reversibility, effectiveness at low pH, and activity under bacteriostatic conditions were examined. The hemolytic activity of nimbolide was also measured. Finally, neem oil extract and nimbolide effectiveness against H. pylori biofilms were examined in comparison to common antibiotics used to treat H. pylori infection.

RESULTS

Nimbolide, but not azadirachtin or gedunin, was effective against H. pylori; MICs and MBCs against the nine tested strains ranged between 1.25-5 μg/mL and 2.5-10 μg/mL, respectively. Additionally, neem oil extract and nimbolide were both effective against H. pylori biofilms. Nimbolide exhibited no significant hemolytic activity at biologically relevant concentrations. The bactericidal activity of nimbolide was time- and dose-dependent, independent of active H. pylori growth, and synergistic with low pH. Furthermore, nimbolide-mediated H. pylori cell death was irreversible after exposure to high nimbolide concentrations (80 μg/mL, after 2 h of exposure time and 40 μg/mL after 8 h of exposure).

CONCLUSIONS

Nimbolide has significant bactericidal activity against H. pylori, killing both free living bacterial cells as well as cells within a biofilm. Furthermore, the lack of hemolytic activity, synergistic activity at low pH and bactericidal properties even against bacteria in a state of growth arrest are all ideal pharmacological and biologically relevant properties for a potential new agent. This study underscores the potential of neem oil extract or nimbolide to be used as a future treatment for H. pylori infection.

Cell density-dependent antibiotic tolerance to inhibition of the elongation machinery requires fully functional PBP1B

The peptidoglycan (PG) cell wall provides shape and structure to most bacteria. There are two systems to build PG in rod shaped organisms: the elongasome and divisome, which are made up of many proteins including the essential MreB and PBP2, or FtsZ and PBP3, respectively. The elongasome is responsible for PG insertion during cell elongation, while the divisome is responsible for septal PG insertion during division. We found that the main elongasome proteins, MreB and PBP2, can be inhibited without affecting growth rate in a quorum sensing-independent density-dependent manner. Before cells reach a particular cell density, inhibition of the elongasome results in different physiological responses, including intracellular vesicle formation and an increase in cell size. This inhibition of MreB or PBP2 can be compensated for by the presence of the class A penicillin binding protein, PBP1B. Furthermore, we found this density-dependent growth resistance to be specific for elongasome inhibition and was consistent across multiple Gram-negative rods, providing new areas of research into antibiotic treatment.

Repurposing the anthelmintic drug niclosamide to combat Helicobacter pylori

There is an urgent need to discover novel antimicrobial therapies. Drug repurposing can reduce the time and cost risk associated with drug development. We report the inhibitory effects of anthelmintic drugs (niclosamide, oxyclozanide, closantel, rafoxanide) against Helicobacter pylori strain 60190 and pursued further characterization of niclosamide against H. pylori. The MIC of niclosamide against H. pylori was 0.25 μg/mL. Niclosamide was stable in acidic pH and demonstrated partial synergy with metronidazole and proton pump inhibitors, such as omeprazole and pantoprazole. Niclosamide administration at 1 × MIC concentration, eliminated 3-log₁₀ CFU of H. pylori adhesion/invasion to AGS cells. Interestingly, no resistance developed even after exposure of H. pylori bacteria to niclosamide for 30 days. The cytotoxic assay demonstrated that niclosamide is not hemolytic and has an IC₅₀ of 4 μg/mL in hepatic and gastric cell lines. Niclosamide administration decreased transmembrane pH as determined by DiSC₃(5) assay indicating that the mechanism of action of the anti-H. pylori activity of niclosamide was the disruption of H. pylori proton motive force. Niclosamide was effective in the Galleria mellonella-H. pylori infection model (p = 0.0001) and it can be develop further to combat H. pylori infection. However, results need to be confirmed with other H. pylori and clinical strains.

Effects of pH on the Antibiotic Resistance of Bacteria Recovered from Diabetic Foot Ulcer Fluid An In Vitro Study

BACKGROUND

This study investigated the resistance of bacteria isolated from diabetic foot ulcers (DFUs) to antibiotics frequently used in the management of the diabetic foot infections, at a range of pH values (pH 6.5, 7.5, and 8.5) known to exist in DFU wound fluid. This study aimed to determine whether changes (or atypical stasis) in wound fluid pH modulate the antibiotic resistance of DFU isolates, with potential implications in relation to the suppression/eradication of bacterial infections in DFUs.

METHODS

Thirty bacterial isolates were recovered from DFU wound fluid, including Staphylococcus spp, Staphylococcus aureus, Escherichia coli, Streptococcus spp, Pseudomonas spp, and Pseudomonas aeruginosa. The resistances of these isolates to a panel of antibiotics currently used in the treatment of infected or potentially infected DFUs, ie, ciprofloxacin, amoxicillin-clavulanate, doxycycline, and piperacillin-tazobactam, at the previously mentioned pH values were determined by a modification of the Kirby-Bauer assay.

RESULTS

The resistance of DFU isolates to clinically relevant antibiotics was significantly affected by the pH levels in DFU wound fluid.

CONCLUSIONS

These findings highlight the importance of a more comprehensive understanding of the conditions in DFUs to inform clinical decision making in the selection and application of antibiotics in treating these difficult-to-heal wounds. The scale of the differences in the efficacies of antibiotics at the different pH values examined is likely to be sufficient to suggest reconsideration of the antibiotics of choice in the treatment of DFU infection.

Activity of a novel protonophore against methicillin-resistant Staphylococcus aureus

AIM

Compound 1-(4-chlorophenyl)-4,4,4-trifluoro-3-hydroxy-2-buten-1-one (compound 1) was identified as a hit against methicillin-resistant Staphylococcus aureus (MRSA) strain MW2.

METHODS & RESULTS

The MIC of compound 1 against MRSA was 4 μg/ml. The compound showed enhanced activity at acidic pH by lowering bacterial intracellular pH and exhibited no lysis of human red blood cells at up to 64 μg/ml and its IC₅₀ against HepG2 cells was 32 μg/ml. The compound reduced 1-log₁₀ colony forming units of intracellular MRSA in macrophages and prolonged the survival of MRSA-infected Caenorhabditis elegans (p = 0.0015) and Galleria mellonella (p = 0.0002).

CONCLUSION

Compound 1 is a protonophore with potent in vitro and in vivo activity against MRSA and no toxicity in mammalian cells up to 8 μg/ml that warrants further investigation as a novel antibacterial.

In vitro activity of levofloxacin against planktonic and biofilm Stenotrophomonas maltophilia lifestyles under conditions relevant to pulmonary infection in cystic fibrosis, and relationship with SmeDEF multidrug efflux pump expression

The activity of levofloxacin against planktonic and biofilm Stenotrophomonas maltophilia cells and the role played by the multidrug efflux pump SmeDEF were evaluated under conditions relevant to the cystic fibrosis (CF) lung. MIC, MBC and MBEC of levofloxacin were assessed, against five CF strains, under 'standard' (CLSI-recommended) and 'CF-like' (pH 6.8, 5% CO2, in a synthetic CF sputum) conditions. Levofloxacin was tested against biofilms at concentrations (10, 50 and 100 μg mL(-1)) corresponding to achievable serum levels and sputum levels by aerosolisation. smeD expression was evaluated, under both conditions, in planktonic and biofilm cells by RT-PCR. The bactericidal effect of levofloxacin was decreased, in three out of five strains tested, under 'CF-like' conditions (MBC: 2-4 vs 8-16 μg mL(-1), under 'standard' and 'CF-like' conditions, respectively). Biofilm was intrinsically resistant to levofloxacin, regardless of conditions tested (MBECs ≥ 100 μg mL(-1) for all strains). Only under 'CF-like' conditions, smeD expression increased during planktonic-to-biofilm transition, and in biofilm cells compared to stationary planktonic cells. Our findings confirmed that S. maltophilia biofilm is intrinsically resistant to therapeutic concentrations of levofloxacin. Under conditions relevant to CF, smeD overexpression could contribute to levofloxacin resistance. Further studies are warranted to define the clinical relevance of our findings.

pH modulates the activity and synergism of the airway surface liquid antimicrobials β-defensin-3 and LL-37

The pulmonary airways are continuously exposed to bacteria. As a first line of defense against infection, the airway surface liquid (ASL) contains a complex mixture of antimicrobial factors that kill inhaled and aspirated bacteria. The composition of ASL is critical for antimicrobial effectiveness. For example, in cystic fibrosis an abnormally acidic ASL inhibits antimicrobial activity. Here, we tested the effect of pH on the activity of an ASL defensin, human β-defensin-3 (hBD-3), and the cathelicidin-related peptide, LL-37. We found that reducing pH from 8.0 to 6.8 reduced the ability of both peptides to kill Staphylococcus aureus. An acidic pH also attenuated LL-37 killing of Pseudomonas aeruginosa. In addition, we discovered synergism between hBD-3 and LL-37 in killing S. aureus. LL-37 and lysozyme were also synergistic. Importantly, an acidic pH reduced the synergistic effects of combinations of ASL antibacterials. These results indicate that an acidic pH reduces the activity of individual ASL antimicrobials, impairs synergism between them, and thus may disrupt an important airway host defense mechanism.

Activity of the investigational fluoroquinolone finafloxacin and seven other antimicrobial agents against 114 obligately anaerobic bacteria

The activity of finafloxacin against 73 strains of the Bacteroides fragilis group, 10 other Gram-negative anaerobic rods and 31 Clostridium difficile strains was determined by the broth microdilution technique. The activity was compared with that of moxifloxacin, levofloxacin, ciprofloxacin, clindamycin, imipenem, piperacillin/tazobactam and metronidazole. MIC(50/90) values (minimum inhibitory concentration, in μg/mL, at which 50% and 90% of the isolates tested are inhibited, respectively) for finafloxacin for the different species were determined: B. fragilis group, 0.5/2; other Gram-negative rods, 0.06/0.25; and C. difficile, 4/16. Furthermore, the MICs against 11 selected B. fragilis strains were determined under acidic conditions and resulted in MIC(50/90) values for finafloxacin of 0.25/4 μg/mL. Thus, finafloxacin shows promising activity against several pathogenic species of anaerobes. Furthermore, finafloxacin has increased activity against selected B. fragilis strains under acidic conditions compared with activity at neutral pH.

Intermolecular interaction of voriconazole analogues with model membrane by DSC and NMR, and their antifungal activity using NMR based metabolic profiling

The development of novel antifungal agents with high susceptibility and increased potency can be achieved by increasing their overall lipophilicity. To enhance the lipophilicity of voriconazole, a second generation azole antifungal agent, we have synthesized its carboxylic acid ester analogues, namely p-methoxybenzoate (Vpmb), toluate (Vtol), benzoate (Vbz) and p-nitrobenzoate (Vpnb). The intermolecular interactions of these analogues with model membrane have been investigated using nuclear magnetic resonance (NMR) and differential scanning calorimetric (DSC) techniques. The results indicate varying degree of changes in the membrane bilayer's structural architecture and physico-chemical characteristics which possibly can be correlated with the antifungal effects via fungal membrane. Rapid metabolite profiling of chemical entities using cell preparations is one of the most important steps in drug discovery. We have evaluated the effect of synthesized analogues on Candida albicans. The method involves real time (1)H NMR measurement of intact cells monitoring NMR signals from fungal metabolites which gives Metabolic End Point (MEP). This is then compared with Minimum Inhibitory Concentration (MIC) determined using conventional methods. Results indicate that one of the synthesized analogues, Vpmb shows reasonably good activity.

The affect of pH and bacterial phenotypic state on antibiotic efficacy

Antibiotics are routinely used in woundcare for the treatment of local and systemic infections. Our goals in this paper were to (i) evaluate the antibiotic sensitivity of bacteria isolated from burn and chronic wounds and (ii) evaluate the effect of pH and bacterial phenotype on the efficacy of antibiotics. Chronic and burn wound isolates, which had been routinely isolated from patients at West Virginia University Hospital, USA, were evaluated for their sensitivity to antibiotics. Antimicrobial susceptibility testing was performed using a standardised disk diffusion assay on agar (quasi/non biofilm) and poloxamer (biofilm). Many of the Gram-positive and -negative isolates demonstrated changes in susceptibility to antibiotics when grown at different pH values and phenotypic states. Findings of this study highlight the clinical relevance that both pH and the phenotypic state of bacteria have on antibiotic performance. The study in particular has shown that bacteria exhibit an enhanced tolerance to antibiotics when grown in the biofilm phenotypic state. Such a finding suggests that more appropriate antibiotic sensitivity testing for woundcare and medicine is warranted to help assist in the enhancement of positive clinical outcomes.

Creeping baselines and adaptive resistance to antibiotics

The introduction of antimicrobial drugs in medicine gave hope for a future in which all infectious diseases could be controlled. Decades later it appears certain this will not be the case, because antibiotic resistance is growing relentlessly. Bacteria possess an extraordinary ability to adapt to environmental challenges like antimicrobials by both genetic and phenotypic means, which contributes to their evolutionary success. It is becoming increasingly appreciated that adaptation is a major mechanism behind the acquisition and evolution of antibiotic resistance. Adaptive resistance is a specific class of non-mutational resistance that is characterized by its transient nature. It occurs in response to certain environmental conditions or due to epigenetic phenomena like persistence. We propose that this type of resistance could be the key to understanding the failure of some antibiotic therapy programs, although adaptive resistance mechanisms are still somewhat unexplored. Similarly, hard wiring of some of the changes involved in adaptive resistance might explain the phenomenon of "baseline creep" whereby the average minimal inhibitory concentration (MIC) of a given medically important bacterial species increases steadily but inexorably over time, making the likelihood of breakthrough resistance greater. This review summarizes the available information on adaptive resistance.

Search for novel antifungal agents by monitoring fungal metabolites in presence of synthetically designed fluconazole derivatives using NMR spectroscopy

Resistance to currently available antifungal drugs necessitates development of new drugs using rapid, robust and automated methods to test a large number of newly synthesized drugs in less time. We have compared the effect of ketoconazole, fluconazole and its synthesized analogues on Candida albicans ATCC 10231. A metabolic profile of C.albicans ATCC 10231 in presence of drugs has been compared using (1)H NMR. Signals from metabolites have been monitored with time. MIC determined using conventional methods has been compared with Metabolic End Point (MEP) obtained from NMR spectroscopy. Results indicate that the activity of the fluconazole derivatives is in the order fluconazole p-methoxybenzoate>fluconazole=fluconazole benzoate>fluconazole toluate>fluconazole p-nitrobenzoate.

Ciprofloxacin/metronidazole versus β-lactam-based treatment of intra-abdominal infections: a meta-analysis of comparative trials

Intra-abdominal infections are polymicrobial and result in substantial morbidity and mortality. The combination of ciprofloxacin/metronidazole as well as several beta-lactam-based regimens are among the commonly used regimens for the treatment of patients with such infections. Thus, we sought to review the evidence from available comparative clinical trials studying ciprofloxacin/metronidazole versus broad-spectrum beta-lactam-based regimens in the treatment of intra-abdominal infections. Studies for the meta-analysis were retrieved from searches of the PubMed database. Five available comparative trials (four randomised controlled trials and one non-randomised comparative trial) including 1431 patients with intra-abdominal infections were included in the meta-analysis. There was a statistically significant difference between the compared arms with regard to cure in favour of the ciprofloxacin/metronidazole combination (odds ratio (OR)=1.69, 95% confidence interval (CI) 1.20-2.39). There was no statistically significant difference between the compared arms with regard to total mortality (OR=1.10, 95% CI 0.71-1.69), mortality attributable to infection (OR=1.42, 95% CI 0.66-3.06) and toxicity (OR=1.25, 95% CI 0.66-2.35). In conclusion, pooled data from the available comparative trials suggest that the ciprofloxacin/metronidazole combination may be superior to beta-lactam-based therapeutic regimens in the treatment of intra-abdominal infections with regard to cure of infections, although no difference in mortality was found.

Diagnosis and treatment of intra-abdominal abscesses

Despite recent advances in the diagnosis and management of intra-abdominal abscesses, these infections still cause substantial morbidity and mortality. Low pH, large bacterial inocula, poor perfusion, the presence of hemoglobin, and large amounts of fibrin (which impedes antibiotic penetration) make the abscess a cloistered environment that is penetrated poorly by many antimicrobial therapies. Therefore, management of these infections requires prompt recognition, early localization, and effective drainage, as well as appropriate antimicrobial use. Although various imaging techniques, such as ultrasonography, gallium scans, and indium-labeled white-blood-cell scans, can be used for the diagnosis and localization of intra-abdominal abscesses, computer-assisted tomography is the most useful study. Once the diagnosis is made and the abscess is localized, treatment should begin promptly. Percutaneous or open surgical drainage should be used. Broad-spectrum antibiotics should be given until culture and sensitivity data are obtained. Once these data are obtained, a therapy with appropriate coverage that is likely to work in the abscess environment should be chosen. Percutaneous drainage is inappropriate for abscesses in the posterior subphrenic space or in the porta hepatis, for those among loops of small bowel, for suspected echinococcal cysts, and for abscesses containing necrotic or neoplastic tissues. Finally, surgeons need to be cognizant of risk factors, such as advanced age, obesity, complex abscesses, and high Acute Physiology and Chronic Health Evaluation (APACHE) II or APACHE III scores, which correlate with poor outcomes for these patients.

Anti-anaerobic activity of antibacterial agents

The first very effective bactericidal anti-anaerobic drug was metronidazole, introduced in clinical practice in the early 1980s. Sometimes penicillin G and chloramphenicol were used successfully in some anaerobic infections. However, this result was most likely due to Gram-positive anaerobic infections (e.g., Clostridium perfringens). Very rapidly, the anti-anaerobic armamentarium was extended with clindamycin, cefoxitin, imipenem and co-amoxyclav or piperacillin-tazobactam. The resistance rate to metronidazole and imipenem remains low but clindamycin has seen an importance decrease in bacterial susceptibility. New additional drugs could be very helpful to overcome resistance and adverse events. The novelties in this field are fluoroquinolones, which exhibit a good activity against Gram-positive cocci and anaerobes.

Meropenem: an updated review of its use in the management of intra-abdominal infections

Meropenem is a carbapenem antibacterial agent with a broad spectrum of activity which encompasses gram-negative, gram-positive and anaerobic bacteria. Like other carbapenems, meropenem is stable against chromosomal and extended-spectrum beta-lactamases. In patients with moderate to severe intra-abdominal infections, empirical monotherapy with meropenem achieved clinical response rates ranging from 91 to 100% in 7 randomised comparative trials. Efficacy rates were similar to those of imipenem/cilastatin (94 to 97%), clindamycin plus tobramycin (93%) and, overall, to cefotaxime plus metronidazole (75 to 100%), although there were differences between trials versus this combination regimen. According to limited data, meropenem also achieved clinical response rates of over 80% in patients with severe intra-abdominal infections. Meropenem is well tolerated, the most common adverse events being diarrhoea, rash, nausea/vomiting and inflammation at the injection site which are reported in <2.5% of patients each. Meropenem also has an improved CNS tolerability profile compared with imipenem/cilastatin.

CONCLUSIONS

Extensive comparative clinical data demonstrate that meropenem can be used effectively as empirical monotherapy in moderate to severe intra-abdominal infections. It also shows potential in the most severe forms of infection, although experience in this infection type remains limited. Compared with standard combination regimens, meropenem offers the benefits of ease of administration without the need for monitoring. It also offers improved CNS tolerability compared with imipenem/cilastatin with the option of a higher maximum dosage, which may be a particular advantage in patients with severe intra-abdominal infections.