Impact of porin deficiency on the synergistic potential of colistin in combination with ß-lactam/ß-lactamase inhibitors against ESBL- and carbapenemase-producing Klebsiella pneumoniae.

Combinations of colistin and ß-lactam/ß-lactamase inhibitors (BLBLIs) have shown in vitro synergy against ß-lactamase-producing strains. However, data are limited and conflicting, potentially attributed to variations among the examined strains. This study investigated whether loss of porins OmpK35 and OmpK36 impacts the synergistic potential of colistin in combination with ceftazidime-avibactam or meropenem-avibactam against ß-lactamase-producing Klebsiella pneumoniae. Genetically modified strains were constructed by introducing blaCTX-M-15, blaKPC-2, and blaOXA-48 chromosomally into K. pneumoniae ATCC 35657, in which the major porin-encoding genes (ompK35, ompK36) were either intact or knocked out. The in vitro activity of colistin in combination with ceftazidime-avibactam or meropenem-avibactam was evaluated by time-lapse microscopy screening and in static time-kill experiments. The deletion of porins in the ß-lactamase-producing strains resulted in 2- to 128-fold increases in MICs for the ß-lactams and BLBLIs. The activity of avibactam was concentration-dependent, and 4- to 16-fold higher concentrations were required to achieve similar inhibition of the ß-lactamases in strains with porin loss. In the screening, synergy was observed for colistin and ceftazidime-avibactam against the CTX-M-15-producing strains and colistin and meropenem-avibactam against the KPC-2- and OXA-48-producing strains. The combination effects were less pronounced in the time-kill experiments, where synergy was rarely detected. No apparent associations were found between the loss of OmpK35 and OmpK36 and combination effects with colistin and BLBLIs, indicating that additional factors determine the synergistic potential of such combinations.

In vivo development of resistance to novel ß-lactam/ß-lactamase inhibitor combinations in KPC-producing Klebsiella pneumoniae infections: a case series.

INTRODUCTION: Understanding the dynamics that may characterize the emergence of KPC variants with resistance to novel ß-lactam/ß-lactamase inhibitor combinations (ßL/ßLICs) represents a challenge to be overcome in the appropriate use of recently introduced antibiotics. METHODS: Retrospective case series describing development of multiple resistance to novel ßL/ßLICs in patients with KPC-producing Klebsiella pneumoniae (KPC-Kp) infections treated with these drugs. Clinical-microbiological investigation and characterization of longitudinal strains by Whole-Genome Sequencing were performed. RESULTS: Four patients with KPC-Kp bloodstream infections were included. Most frequent clinical features were kidney disease, obesity, cardiac surgery as reason for admission, ICU stay, treatment with ceftazidime/avibactam, and pneumonia and/or acute kidney injury needing renal replacement therapy as KPC-Kp sepsis-associated complications. The development of resistance to ceftazidime/avibactam was observed in four longitudinal strains (three of which were co-resistant to aztreonam/avibactam and cefiderocol) following treatments with ceftazidime/avibactam (n = 3) or cefiderocol (n = 1). Resistance to meropenem/vaborbactam and imipenem/cilastatin/relebactam was observed in one case after exposure to ceftazidime/avibactam and imipenem/cilastatin/relebactam. Resistome analysis showed that resistance to novel ßL/ßLICs was related to specific mutations within blaKPC carbapenemase gene (D179Y mutation [KPC-33]; deletion Δ242-GT-243 [KPC-14]) in three longitudinal strains, while porin loss (truncated OmpK35 and OmpK36 porins) was observed in one case. CONCLUSION: Therapy with novel ßL/ßLICs or cefiderocol may lead to the selection of resistant mutants in the presence of factors influencing the achievement of PK/PD targets. KPC variants are mainly associated with resistance to ceftazidime/avibactam, and some of them (e.g. KPC-14) may also be associated with reduced susceptibility to aztreonam/avibactam and/or cefiderocol. Loss of function of the OmpK35 and OmpK36 porins appears to play a role in the development of resistance to meropenem/vaborbactam and/or imipenem/relebactam, but other mechanisms may also be involved.

An Atypical Presentation of Acute Generalized Exanthematous Pustulosis Induced by Use of Meropenem: A Case Report and Literature Review.

Acute generalized exanthematous pustulosis (AGEP) is a rare dermatological disorder characterized by the development of sterile pustular lesions on erythematous and edematous skin, followed by desquamation of the affected regions. The majority of cases occur following the administration of antimicrobials and antihypertensives. Our case report illustrates the atypical presentation of AGEP in an elderly female following treatment with meropenem for an infected pressure ulcer. Only a limited number of meropenem-associated AGEP have been documented. Our patient's presentation also highlights the difficulty of diagnosing AGEP and its similarity to other rare, drug-associated rashes. By illustrating this atypical clinical presentation of AGEP and highlighting its association with meropenem, we hope to provide insight to clinicians dealing with similar presentations.

Multi-omics approach for understanding the response of Bacteroides fragilis to carbapenems.

Background: The prevalence of Bacteroides fragilis isolates resistant to first-line beta-lactam drugs is increasing, resulting in reduced treatment efficacy. Investigating the bacterial transcriptome and proteome can uncover links between bacterial genes and resistance mechanisms. In this study, we experimentally assessed in vitro the transcriptional and proteomic profiles of B. fragilis exposed to SICs of meropenem, an effective antimicrobial agent, collected from patients with intra-abdominal diseases at Astana City Hospital, Kazakhstan. Methods: B. fragilis was cultured in brain heart infusion broth and sub-cultured every 48 h for 8 days in media with and without meropenem. Total RNA was extracted from the liquid cultures using a commercial RNeasy mini kit, and strand-specific RNA sequencing (RNA-seq) was performed on the DNBSEQ platform. Raw RNA-seq data were retrieved from BioProject No. PRJNA531645 and uploaded to the NCBI Sequence Read Archive (accession no. SRX22081155). Proteins of B. fragilis were extracted and separated using sodium dodecyl sulphate-polyacrylamide gel electrophoresis, followed by analysis of the eluted peptides using liquid chromatography-tandem mass spectrometry. Cluster analysis utilised the Database for Annotation, Visualisation, and Integrated Discovery. Results: The subinhibitory concentration (SIC) of meropenem was determined to be 0.5 µg/L (minimum inhibitory concentration: 1). Mapping of reads to the reference genome identified 2477 expressed genes in all B. fragilis BFR KZ01 samples. Ten differentially expressed genes (DEGs) were common across comparison groups during and post-antibiotic exposure (wMEM vs. MEM2 and MEM2 vs. rMEM8); however, no substantially enriched Gene Ontology terms were identified. The cluster analysis highlighted a significant enrichment cluster (W-0560 oxidoreductase) of DEGs following antibiotic withdrawal. In total, 859 B. fragilis proteins were identified, with the expressions of three proteins, 3-oxoacyl-[acyl carrier protein] reductase, acetyl-CoA carboxylase biotin carboxylase subunit, and beta-ketoacyl-ACP synthase III, being upregulated in the enriched protein folding category. Notably, chaperone proteins such as FKBP-type peptidyl-prolyl cis-trans isomerases (involved in the cis-trans isomerisation of prolyl peptide bonds) and GroES (a co-chaperone functioning with GroEL) were also identified. Conclusions: Under the influence of low doses of antibiotics defense mechanisms are activated which contribute to the emergence of resistance. These results provide insight into the response of B. fragilis to meropenem exposure, mainly at the SIC, contributing to the understanding bacterial survival strategies under stress conditions.

Population pharmacokinetics and dosing simulations of meropenem in septic critically ill patients with complicated intra-abdominal infection or pneumonia.

OBJECTIVES: Meropenem pharmacokinetics (PK) may be altered in septic critically ill patients with complicated intra-abdominal infections (cIAI) and pneumonia. We aimed to evaluate the covariates affecting meropenem PK and the performance of different dosing regimens to optimize the PK/pharmacodynamic target. METHODS: Population PK analysis was performed using non-linear mixed-effects modeling. The final model was validated and used to simulate meropenem exposure to assess the probability of attaining the 100%ƒT>MIC target. RESULTS: Forty-six and 14 patients were respectively enrolled for PK analysis and external validation. A one-compartment linear model adequately described the data of 226 concentrations. The typical clearance (CL) and volume of distribution (Vd) were 9.69 L/h and 27.4 L, respectively. Septic shock from cIAI (cIASS) and actual body weight were significant covariates for meropenem Vd in addition to the influential covariates of creatinine clearance (CLCR-CG) and augmented renal clearance for CL. External validation showed the robustness and accuracy of this model. Simulation results proposed continuous infusion (CI) dosing regimens of meropenem against pathogens with MICs ≥ 2 mg/L in patients with cIASS and CLCR-CG ≥ 60 mL/min. CONCLUSIONS: For the patients with cIASS and CLCR-CG ≥ 60 mL/min, CI meropenem is proposed for treatment of less sensitive pathogens with MICs ≥ 2 mg/L.

First Case Report of Mycotic Abdominal Aortic Aneurysm Caused by Campylobacter fetus in Serbia.

BACKGROUND: Due to its distinct vascular tropism, Campylobacter fetus is recognized as a significant cause of severe systemic infections, especially in immunocompromised individuals, while it is rarely reported as a cause of gastrointestinal infections. METHODS: A rare case of mycotic abdominal aortic aneurysm associated with Campylobacter fetus detected on the aneurysm wall itself was described. RESULTS: A 68-year-old male was admitted to the hospital due to severe abdominal pain. The patient was afebrile, hemodynamically stable with elevated C-reactive protein levels. A physical examination revealed a palpable, pulsatile, tender mass located in the periumbilical region. Ultrasonography and multi-slice computer tomography angiography (MSCTA) identified an infrarenal abdominal aortic aneurysm with a maximum diameter of 6.5 cm, showing suspicious signs of dissection. Aneurysmectomy with Dacron tube graft interposition was performed. Although the blood cultures remained negative, the culture of the aneurysmal wall grew Campylobacter fetus, enabling early diagnosis and targeted antibiotic therapy. The patient was treated with meropenem for two weeks, followed by amoxicillin-clavulanate for another two weeks after hospital discharge. CONCLUSIONS: Campylobacter fetus associated with abdominal aortic aneurysms represents a life-threatening condition, posing a significant challenge in vascular surgery. Due to the lack of clear guidelines on antibiotic susceptibility testing and the treatment of infections associated with this pathogen, enhanced surveillance of Campylobacter fetus is necessary in both human and veterinary medicine.

Physiologically-based pharmacokinetic modelling in sepsis; a tool to elucidate how pathophysiology affects meropenem pharmacokinetics: A PBPK model of meropenem in sepsis.

Applying physiologically-based pharmacokinetic (PBPK) modelling in sepsis could help to better understand how PK changes are influenced by drug- and patient-related factors. We aimed to elucidate the influence of sepsis pathophysiology on the PK of meropenem by applying PBPK modelling. A whole-body meropenem PBPK model was developed and evaluated in healthy individuals, and renally impaired non-septic patients. Sepsis-induced physiological changes in body composition, organ blood flow, kidney function, albumin, and haematocrit were implemented according to a previously proposed PBPK sepsis model. Model performance was evaluated, and a local sensitivity analysis was conducted. The model-predicted PK metrics (AUC, Cmax, CL, Vss) were within 1.33-fold-error margin of published data for 87.5% of the simulated profiles in healthy individuals. In sepsis, the model provided good predictions for literature-digitised average plasma and tissue exposure data, where the model-predicted AUC was within 1.33-fold-error margin for 9 out 11 simulated study profiles. Furthermore, the model was applied to individual plasma concentration data from 52 septic patients, where the model-predicted AUC, Cmax, and CL had a fold-error ratio range of 0.98-1.12, with alignment of the predicted and observed variability. For Vss, the fold-error ratio was 0.81, and the model underpredicted the population variability. CL was sensitive to renal plasma clearance, and kidney volume, whereas Vss was sensitive to the unbound fraction, organ volume fraction of the interstitial compartment, and the organ volume. These findings may be extended to more diverse drug types and support a more mechanistic understanding of the effect of sepsis on drug exposure.

Effect of Ceftaroline, Ceftazidime/Avibactam, Ceftolozane/Tazobactam, and Meropenem/Vaborbactam on Establishment of Colonization by Vancomycin-Resistant Enterococci and Klebsiella pneumoniae in Mice.

Background: The potential for promotion of intestinal colonization with healthcare-associated pathogens by new antibiotics used to treat infections due to multidrug-resistant Gram-negative bacilli is unclear. Methods: Mice treated for 3 days with daily subcutaneous phosphate-buffered saline (control), ceftazidime/avibactam, ceftolozane/tazobactam, ceftaroline, and meropenem/vaborbactam were challenged with 10,000 colony-forming units (CFU) of vancomycin-resistant Enterococcus (VRE) resistant to each of the antibioics or carbapenemase-producing Klebsiella pneumoniae 1 day after the final treatment dose. The concentrations of VRE or K. pneumoniae in stool were measured on days 1, 3, 6, and 15 after challenge. Results: Control mice had transient low levels of VRE or K. pneumoniae (<3 log10 CFU/g) detected in stool with negative cultures on days 6 and 15 after challenge. In comparison to control mice, each of the antibiotics promoted establishment of high-density colonization with VRE (mean concentration, >8 log10 CFU/g of stool on day 1 after challenge) that persisted at >4 log10 CFU/g of stool through day 15 (P<0.01). In comparison to control mice, meropenem/vaborbactam and ceftaroline promoted high-density colonization with K. pneumoniae (peak concentration, >8 log10 CFU/g of stool) (P<0.01), ceftolozane/tazobactam promoted colonization to a lesser degree (peak concentration, >5 log10 CFU/g of stool), and ceftazidime/avibactam did not promote colonization (P>0.05). Conclusions: Our results suggest that several beta-lactam antibiotics recently developed for treatment of infections with resistant Gram-negative bacilli have the potential to promote colonization by healthcare-associated pathogens. Additional studies are needed to examine the impact of these agents in patients.

Anticancer agent 5-fluorouracil reverses meropenem resistance in carbapenem-resistant Gram-negative pathogens.

The global increasing incidence of clinical infections caused by carbapenem-resistant Gram-negative pathogens requires urgent and effective treatment strategies. Antibiotic adjuvants represent a promising approach to enhance the efficacy of meropenem against carbapenem-resistant bacteria. This study shows that the anticancer agent 5-fluorouracil (5-FU, 50 µM) significantly reduced the minimum inhibitory concentration of meropenem against blaNDM-5 positive Escherichia coli by 32-fold through cell-based high-throughput screening. Further pharmacological studies indicated that 5-FU exhibited potentiation effects on carbapenem antibiotics against 42 Gram-negative bacteria producing either metallo-ß-lactamases (MBLs), such as NDM and IMP, or serine ß-lactamases (Ser-BLs), like KPC and OXA. These bacteria included E. coli, Klebsiella pneumoniae, Pseudomonas aeruginosa and Acinetobacter spp., 32 of which were obtained from human clinical samples. Mechanistic investigations revealed that 5-FU inhibited the transcription and expression of the blaNDM-5 gene. In addition, 5-FU combined with meropenem enhanced bacterial metabolism, and stimulated the production of reactive oxygen species (ROS), thereby rendering bacteria more susceptible to meropenem. In a mouse systemic infection model, 5-FU combined with meropenem reduced bacterial loads and effectively elevated the survival rate of 83.3%, compared with 16.7% with meropenem monotherapy. Collectively, these findings indicate the potential of 5-FU as a novel meropenem adjuvant to improve treatment outcomes against infections caused by carbapenem-resistant bacteria.

A Retrospective Analysis of Intravenous Push versus Extended Infusion Meropenem in Critically Ill Patients.

Meropenem is a broad-spectrum antibiotic used for the treatment of multi-drug-resistant infections. Due to its pharmacokinetic profile, meropenem's activity is optimized by maintaining a specific time the serum concentration remains above the minimum inhibitory concentration (MIC) via extended infusion (EI), continuous infusion, or intermittent infusion dosing strategies. The available literature varies regarding the superiority of these dosing strategies. This study's primary objective was to determine the difference in time to clinical stabilization between intravenous push (IVP) and EI administration. We performed a retrospective pilot cohort study of 100 critically ill patients who received meropenem by IVP (n = 50) or EI (n = 50) during their intensive care unit (ICU) admission. There was no statistically significant difference in the overall achievement of clinical stabilization between IVP and EI (48% vs. 44%, p = 0.17). However, the median time to clinical stability was shorter for the EI group (20.4 vs. 66.2 h, p = 0.01). EI administration was associated with shorter hospital (13 vs. 17 days; p = 0.05) and ICU (6 vs. 9 days; p = 0.02) lengths of stay. Although we did not find a statistically significant difference in the overall time to clinical stabilization, the results of this pilot study suggest that EI administration may produce quicker clinical resolutions than IVP.

Precision Dosing of Meropenem in Adults with Normal Renal Function: Insights from a Population Pharmacokinetic and Monte Carlo Simulation Study.

This study aimed to develop a population pharmacokinetic (PK) model for meropenem in healthy adults and explore optimal dosing regimens for patients with normal renal function. PK samples were obtained from 12 healthy participants, which were analyzed using noncompartmental analysis and nonlinear mixed-effect modeling. The PK profiles of meropenem were characterized using a two-compartment model, and serum creatinine level was identified as a significant covariate affecting total clearance. Monte Carlo simulations were conducted using this model to inform dosing recommendations. The target index for meropenem efficacy was defined as the cumulative percentage over 24 h during which free (f) drug concentration exceeded the minimum inhibitory concentration (MIC) under steady state conditions (fT>MIC). These simulations indicated that the current dosage regimen of 1 g for 30 min infusions every 8 h achieved a 90% probability of target attainment (PTA) for 40%fT>MIC when the MIC was <2 mg/L. However, to achieve more stringent therapeutic targets, such as a 90%PTA for 100%fT>MIC or a 90%PTA for 100%fT>4MIC, higher doses administered as 3 h extended infusions or as continuous infusions may be necessary. These results highlight the need for model-informed precision dosing to enhance the efficacy of meropenem therapy across various MIC levels and therapeutic targets.

Diagnostic Test Precision of Modified Carbapenem Inactivation Method and Carbapenemase Nordmann-Poirel Test for Phenotypic Detection of Carbapenemase Production in Enterobacterales: A Systematic Review.

Carbapenem-resistant Enterobacterales, particularly those that produce carbapenemases, pose a significant public health concern due to very limited treatment options. The timely identification of carbapenemase-producing Enterobacterales (CPE) is essential for putting in place efficient infection control measures and selecting appropriate antimicrobial therapies, thereby improving the clinical outcome of the patient. The purpose of this systematic review is to compare the diagnostic accuracy and practicality between two phenotypic tests, namely the modified carbapenem inactivation method (mCIM) and carbapenemase Nordmann-Poirel (Carba NP) test, in detecting carbapenemase production by Enterobacterales and thereby aiding the clinician in making a decision to choose an appropriate test for their phenotypic detection. This systematic review involved combining sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), accuracy, diagnostic odds ratio with 95% confidence interval (CIs), Forest plot for sensitivity and specificity, and plotting suitable summary receiver operating characteristic curve with the area under the curve. Of the 20 studies included in this review, the overall effect sizes of Carba NP and mCIM with 95% CIs were as follows: sensitivity, 91% (86-96%) and 97% (95-99%); specificity, 93% (88-97%) and 97% (93-100%); PPV, 97% and 98%; NPV, 79% and 90%; accuracy, 93% and 97%; diagnostic odds ratio, 1487.8879 and 8527.5541; and AUC, 0.85 and 1, respectively. In conclusion, the mCIM method showed superior sensitivity (97%), specificity (97%), and accuracy compared to the Carba NP test in detecting carbapenemase production, even though both these methods had a few technical limitations. The Carba NP test is rapid, affordable, and dependable, whereas mCIM is more accurate and cost-effective but time-consuming. We propose that both tests can be reliably used for screening of carbapenemase production in Enterobacterales, as endorsed by the Clinical and Laboratory Standards Institute even in resource-limited clinical laboratories, in the order of prioritizing the mCIM method first and then followed by the Carba NP test when situation demands expedited results.

Systematic Review and Meta-Analysis of Clinical Efficacy and Safety of Meropenem-Vaborbactam versus Best-Available Therapy in Patients with Carbapenem-Resistant Enterobacteriaceae Infections.

Antimicrobial resistance is increasingly concerning, causing millions of deaths and a high cost burden. Given that carbapenemase-producing Enterobacterales are particularly concerning due to their ability to develop structural modifications and produce antibiotic-degrading enzymes, leading to high resistance levels, we sought to summarize the available data on the efficacy and safety regarding the combination of meropenem-vaborbactam (MV) versus the best available therapy (BAT). Articles related to our objective were searched in the PubMed and Scopus databases inception to July 2024. To assess the quality of the studies, we used the Cochrane risk-of-bias tool, RoB2. The outcomes were pooled as a risk ratio (RR) and a 95% confidence interval (95%CI). A total of four published studies were involved: one retrospective cohort study and three phase 3 trials, including 432 patients treated with MV and 426 patients treated with BAT (mono/combination therapy with polymyxins, carbapenems, aminoglycosides, colistin, and tigecycline; or ceftazidime-avibactam; or piperacillin-tazobactam). No significant difference in the clinical response rate was observed between MV and the comparators at the TOC (RR = 1.29, 95%CI [0.92, 1.80], p = 0.14) and EOT (RR = 1.66, 95%CI [0.58, 4.76], p = 0.34) visits. MV was associated with a similar microbiological response as the comparators at TOC (RR = 1.63, 95%CI [0.85, 3.11], p = 0.14) and EOT assessment (RR = 1.16, 95%CI [0.88, 1.54], p = 0.14). In the pooled analysis of the four studies, 28-day all-cause mortality was lower for MV than the control groups (RR = 0.47, 95%CI [0.24, 0.92], p = 0.03). MV was associated with a similar risk of adverse events (AEs) as comparators (RR = 0.79, 95%CI [0.53, 1.17], p = 0.23). Additionally, MV was associated with fewer renal-related AEs than the comparators (RR = 0.32, 95%CI [0.15, 0.66], p = 0.002). MV was associated with a similar risk of treatment discontinuation due to AEs (RR = 0.76, 95%CI [0.38, 1.49], p = 0.42) or drug-related AEs (RR = 0.56, 95%CI [0.28, 1.10], p = 0.09) as the comparators. In conclusion, MV presents a promising therapeutic option for treating CRE infections, demonstrating similar clinical and microbiological responses as other comparators, with potential advantages in mortality outcomes and renal-related AEs.

Association between Extended Meropenem Regimen and Achievement of Aggressive PK/PD in Patients Receiving Continuous Renal Replacement Therapy for Septic AKI.

Aggressive pharmacokinetic (PK)/pharmacodynamic (PD) targets have shown better microbiological eradication rates and a lower propensity to develop resistant strains than conservative targets. We investigated whether meropenem blood levels, including aggressive PK/PD, were acceptable in terms of efficacy and safety using a meropenem regimen of 1 g infusion every 8 h over 3 h in patients undergoing continuous renal replacement therapy (CRRT) for septic acute kidney injury (AKI). Aggressive PK/PD targets were defined as the percentage of time that the free concentration (%fT) > 4 × minimal inhibitory concentration (MIC), the toxicity threshold was defined as a trough concentration >45 mg/L, and the percentage of achievement at each MIC was evaluated. The 100% fT > 4 × MIC for a pathogen with an MIC of 0.5 mg/L was 89%, and that for a pathogen with an MIC of 2 mg/L was 56%. The mean steady-state trough concentration of meropenem was 11.9 ± 9.0 mg/L and the maximum steady-state trough concentration was 29.2 mg/L. Simulations using Bayesian estimation showed the probability of achieving 100% fT > 4 × MIC for up to an MIC of 2 mg/L for the administered administration via continuous infusion at 3 g/24 h. We found that an aggressive PK/PD could be achieved up to an MIC of 0.5 mg/L with a meropenem regimen of 1 g infused every 8 h over 3 h for patients receiving CRRT for septic AKI. In addition, the risk of reaching the toxicity range with this regimen is low. In addition, if the MIC was 1-2 mg/L, the simulation results indicated that aggressive PK/PD can be achieved by continuous infusion at 3 g/24 h without increasing the daily dose.

Reversion of KPC-114 to KPC-2 in ceftazidime-avibactam- resistant/meropenem-susceptible Klebsiella pneumoniae ST11 is related to low mutation rates.

Klebsiella pneumoniae strains that produce Klebsiella pneumoniae Carbapenemase (KPC) variants displaying resistance to ceftazidime-avibactam (CZA) often remain susceptible to meropenem (MEM), suggesting a potential therapeutic use of this carbapenem antibiotic. However, in vitro studies indicate that these sorts of strains can mutate becoming MEM-resistant, raising concerns about the effectiveness of carbapenems as treatment option. We have studied mutation rates occurring from the reversion of MEM-susceptible KPC-114 to MEM-resistant KPC-2, in CZA-resistant K. pneumoniae belonging to ST11. Two-step fluctuation assays (FAs) were conducted. In brief, initial cultures of KPC-114-producing K. pneumoniae showing 1 µg/mL MEM MIC were spread on Mueller-Hinton agar plates containing 2-8 µg/mL MEM. A second step of FA, at 4-16 µg/mL MEM was performed from a mutant colony obtained at 2 µg/mL MEM. Mutation rates were calculated using maximum likelihood estimation. Parental and mutant strains were sequenced by Illumina NextSeq, and mutations were predicted by variant-calling analysis. At 8 µg/mL MEM, mutants derived from parental CZA-resistant (MIC ≥ 64 µg/mL)/MEM-susceptible (MIC = 1 µg/mL) KPC-114-positive K. pneumoniae exhibited an accumulative mutation rate of 3.05 × 10-19 mutations/cell/generation, whereas at 16 µg/mL MEM an accumulative mutation rate of 1.33 × 10-19 mutations/cell/generation resulted in the reversion of KPC-114 (S181_P182 deletion) to KPC-2. These findings highlight that the reversion of MEM-susceptible KPC-114 to MEM-resistant KPC-2, in CZA-resistant K. pneumoniae ST11 is related to low mutation rates suggesting a low risk of therapeutic failure. In vivo investigations are necessary to confirm the clinical potential of MEM against CZA-resistant KPC variants.IMPORTANCEThe emergence of ceftazidime-avibactam (CZA) resistance among carbapenem-resistant Klebsiella pneumoniae is a major concern due to the limited therapeutic options. Strikingly, KPC mutations mediating CZA resistance are generally associated with meropenem susceptibility, suggesting a potential therapeutic use of this carbapenem antibiotic. However, the reversion of meropenem-susceptible to meropenem-resistant could be expected. Therefore, knowing the mutation rate related to this genetic event is essential to estimate the potential use of meropenem against CZA-resistant KPC-producing K. pneumoniae. In this study, we demonstrate, in vitro, that under high concentrations of meropenem, reversion of KPC-114 to KPC-2 in CZA-resistant/meropenem-susceptible K. pneumoniae belonging to the global high-risk ST11 is related to low mutation rates.

Current trend of biapenem susceptibility and disc diffusion breakpoints in Enterobacterales and Pseudomonas aeruginosa.

INTRODUCTION: Biapenem has been recently approved by the Drug Controller General of India for the treatment of complicated urinary tract infections (cUTI). However, there are no assessment studies that evaluate the in-vitro activity of biapenem against contemporary ESBL-producing Indian Enterobacterales isolates. To determine the activity of biapenem against contemporary ESBLs and/or OXA-1/ampC producing Enterobacterales and Pseudomonas aeruginosa isolates. METHODOLOGY: Isolates were tested for susceptibility to biapenem and its comparators using the broth microdilution method. Presence of ESBLs (SHV, TEM, CTX-M) genes, OXA-1, and ampC genes (ACC, ACT, DHA, CIT/CMY, FOX) using multiplex PCR. RESULTS: Against ESBL with OXA-1 and/or ampC-producing E. coli, ESBL-K. pneumoniae, and cephalosporin-resistant P. aeruginosa, biapenem showed in-vitro activity similar to that of meropenem. Overall, a biapenem disc concentration of 10 µg provided no error rates for testing E. coli, K. pneumoniae, and P. aeruginosa isolates. CONCLUSION: It is more accurate to test biapenem at a 10 µg disc concentration and apply more stringent disc diffusion breakpoints for interpretation.

Acinetobacter baumannii transformants expressing oxacillinases and metallo-ß-lactamases that confer resistance to meropenem: new tools for anti-Acinetobacter drug development and AMR preparedness.

Antimicrobial resistance (AMR) in Acinetobacter baumannii is an unmet medical need. Multiple drug-resistant/extremely drug-resistant strains of A. baumannii do not display growth well in in vivo models, and consequently, their response to antibacterial therapy is inconsistent. We addressed this issue by engineering carbapenem resistance motifs into the highly virulent genetic background of A. baumannii AB5075. This strain has a chromosomally encoded oxa-23 that was deleted (Δoxa-23), then plasmids expressing oxa-23, oxa-24/40, oxa-58, imp-1, vim-2, and ndm-1 were introduced to create the mutant strains. Each transformant was used as a challenge strain in a neutropenic murine thigh infection model and assessed for the extent of growth and response to meropenem 200 mg/kg subcutaneously every 6 h (q6h). Pharmacodynamic analyses were performed by transforming drug exposure from dose (mg/kg) to the fraction of the dosing interval; free meropenem concentrations were >minimum inhibitory concentration (MIC) (fT > MIC). AB5075 and the AB5075Δoxa-23 mutant had a MICs of 32 and 4 mg/L, respectively. The transformants harboring oxacillinases oxa-24/40 and oxa-58 had an MIC of 64 mg/L. The metallo-ß-lactamases imp-1, vim-2, and ndm-1 had MICs of 128, 64, and 64 mg/L, respectively. All vehicle-treated transformants displayed in vivo growth in the range of 0.75-1.4 log. The response to meropenem was consistent with the varying fT > MIC of the transformants and was readily described by an inhibitory sigmoid Emax relationship. Stasis was achieved with a fT > MIC of 0.36. These A. baumannii transformants are invaluable new tools for the assessment of anti-Acinetobacter compounds and provide a new pathway for AMR preparedness.

The Immediate and Delayed Maximal Nonirritating Skin Testing Concentrations of ß-Lactam Antibiotics.

BACKGROUND: Maximal skin testing (ST) nonirritant concentrations (NICs) are consistent for penicillin and aminopenicillin among guidelines. However, there is variability among guidelines for maximal ST NICs of cephalosporins. OBJECTIVE: To determine maximal immediate and delayed ST NICs of 15 ß-lactams in ß-lactam-tolerant and ß-lactam-naïve participants. METHODS: We performed a single-center, nonrandomized prospective study between September 2019 and January 2022 in adult participants. Participants received skin prick testing (SPT) and intradermal test (IDT) injections at 6 increasing concentrations of 1 or more ß-lactams. A concentration was considered irritant when more than 5% of participants had a positive test. A positive test was defined as a wheal ≥3 mm compared with negative control accompanied by a ≥5 mm flare for SPT/IDT and induration ≥5 mm with associated erythema at 48 hours for delayed readings (dIDT). Sensitivity analyses using 3 alternative IDT positive criteria were conducted. RESULTS: A total of 747 participants with a median age of 64 (interquartile range: 54-72) years (52% male, 85% White, and 92% non-Hispanic) underwent 20,858 skin tests. All undiluted SPT concentrations were nonirritant. We found the following maximal IDT/dIDT NICs (mg/mL): ampicillin (41.6/125), ampicillin-sulbactam (93.8/187.5), aztreonam (6.3/25), cefazolin (55/165), cefepime (35/140), cefoxitin (45/90), ceftaroline (7.5/15), ceftriaxone (58.3/175), cefuroxime (55/110), ertapenem (16.6/50), imipenem-cilastin (6.3/25), meropenem (8.3/25), nafcillin (31.3/62.5), oxacillin (20.9/83.5), and piperacillin-tazobactam (112.5/225). dIDTs were almost all completely nonirritant close to or at undiluted concentrations. There were no differences when we applied 3 IDT positivity criteria to our raw data. CONCLUSIONS: Our results suggest that SPTs with undiluted stock ß-lactam antibiotic concentrations are nonirritant. Compared with previously published nonirritant concentrations, we propose a 2- to 50-fold increase to the maximal IDT and dIDT NICs of 15 ß-lactam antibiotics. When performing dIDTs, a higher concentration should be used rather than the same IDT concentration.

Is the high dose extended infusion of meropenem useful in the treatment of highly resistant gram-negative bacteria in children?

OBJECTIVES: Multidrug resistant infections present a treatment challenge for clinicians. These infections have been associated with increased morbidity and mortality. Recently, there has been increasing discussion in the literature that high dose extended infusion of meropenem may be helpful. We aimed to evaluate the clinical efficacy of high dose extended infusion of meropenem in the treatment of highly resistant Gram-negative infections. METHODS: This retrospective observational study was conducted between December 2014 and December 2020 at Hacettepe University Ihsan Dogramaci Children's Hospital. Clinical and microbiological data of children diagnosed with invasive multidrug and extremely drug resistant Gram-negative infections were studied. The findings of patients given high dose extended infusion of meropenem were compared with patients who received colistin or tigecycline. RESULTS: Overall, 158 pediatric patients infected with multidrug and extremely drug resistant gram-negatives were enrolled; 76 treated with high-dose prolonged infusion of meropenem; 60 treated with colistin and 22 with tigecycline. The overall clinical response at the end of the treatment was 81.6 % in meropenem group, 83.3 % in colistin group and 77.3 % in tigecycline group (P = 0.821). Microbiological response at the end of the treatment was 81.1 % in meropenem group, 76.4 % in colistin group and 72.2 % in tigecycline group (P = 0.694). CONCLUSION: Meropenem, with an adjusted dose (high-dose and extended), seems a crucial and robust fighting agent in the treatment of pediatric patients infected with highly-resistant Gram-negative bacteria. It may also be useful in preventing the use of the latest fighting tools such as colistin and tigecycline during the antibacterial stewardship process.

Physiologically-based pharmacokinetic/pharmacodynamic modeling of meropenem in critically ill patients.

This study aimed to develop a physiologically based pharmacokinetic/pharmacodynamic model (PBPK/PD) of meropenem for critically ill patients. A PBPK model of meropenem in healthy adults was established using PK-Sim software and subsequently extrapolated to critically ill patients based on anatomic and physiological parameters. The mean fold error (MFE) and geometric mean fold error (GMFE) methods were used to compare the differences between predicted and observed values of pharmacokinetic parameters Cmax, AUC0-∞, and CL to evaluate the accuracy of the PBPK model. The model was verified using meropenem plasma samples obtained from Intensive Care Unit (ICU) patients, which were determined by HPLC-MS/MS. After that, the PBPK model was combined with a PKPD model, which was developed based on f%T > MIC. Monte Carlo simulation was utilized to calculate the probability of target attainment (PTA) in patients. The developed PBPK model successfully predicted the meropenem disposition in critically ill patients, wherein the MFE average and GMFE of all predicted PK parameters were within the 1.25-fold error range. The therapeutic drug monitoring (TDM) of meropenem was conducted with 92 blood samples from 31 ICU patients, of which 71 (77.17%) blood samples were consistent with the simulated value. The TDM results showed that meropenem PBPK modeling is well simulated in critically ill patients. Monte Carlo simulations showed that extended infusion and frequent administration were necessary to achieve curative effect for critically ill patients, whereas excessive infusion time (> 4 h) was unnecessary. The PBPK/PD modeling incorporating literature and prospective study data can predict meropenem pharmacokinetics in critically ill patients correctly. Our study provides a reference for dose adjustment in critically ill patients.