Crystal structure of the class A extended-spectrum ß-lactamase CTX-M-96 in complex with relebactam at 1.03 Angstrom resolution.

The use of ß-lactam/ß-lactamase inhibitors constitutes an important strategy to counteract ß-lactamases in multidrug-resistant (MDR) Gram-negative bacteria. Recent reports have described ceftazidime-/avibactam-resistant isolates producing CTX-M variants with different amino acid substitutions (e.g., P167S, L169Q, and S130G). Relebactam (REL) combined with imipenem has proved very effective against Enterobacterales producing ESBLs, serine-carbapenemases, and AmpCs. Herein, we evaluated the inhibitory efficacy of REL against CTX-M-96, a CTX-M-15-type variant. The CTX-M-96 structure was obtained in complex with REL at 1.03 Å resolution (PDB 8EHH). REL was covalently bound to the S70-Oγ atom upon cleavage of the C7-N6 bond. Compared with apo CTX-M-96, binding of REL forces a slight displacement of the deacylating water inwards the active site (0.81 Å), making the E166 and N170 side chains shift to create a proper hydrogen bonding network. Binding of REL also disturbs the hydrophobic patch formed by Y105, P107, and Y129, likely due to the piperidine ring of REL that creates clashes with these residues. Also, a remarkable change in the positioning of the N104 sidechain is also affected by the piperidine ring. Therefore, differences in the kinetic behavior of REL against class A ß-lactamases seem to rely, at least in part, on differences in the residues being involved in the association and stabilization of the inhibitor before hydrolysis. Our data provide the biochemical and structural basis for REL effectiveness against CTX-M-producing Gram-negative pathogens and essential details for further DBO design. Imipenem/REL remains an important choice for dealing with isolates co-producing CTX-M with other ß-lactamases.

Effect of modification of penicillin-binding protein 3 on susceptibility to ceftazidime-avibactam, imipenem-relebactam, meropenem-vaborbactam, aztreonam-avibactam, cefepime-taniborbactam, and cefiderocol of Escherichia coli strains producing broad-spectrum ß-lactamases.

The impact of penicillin-binding protein 3 (PBP3) modifications that may be identified in Escherichia coli was evaluated with respect to susceptibility to ß-lactam/ß-lactamase inhibitor combinations including ceftazidime-avibactam, imipenem-relebactam, meropenem-vaborbactam, aztreonam-avibactam, cefepime-taniborbactam, and to cefiderocol. A large series of E. coli recombinant strains producing broad-spectrum ß-lactamases was evaluated. While imipenem-relebactam showed a similar activity regardless of the PBP3 background, susceptibility to other molecules tested was affected at various levels. This was particularly the case for ceftazidime-avibactam, aztreonam-avibactam, and cefepime-taniborbactam.

In vitro activity of cefoxitin, imipenem, meropenem, and ceftaroline in combination with vaborbactam against Mycobacterium abscessus.

Mycobacterium abscessus (MAB) infections pose a growing public health threat. Here, we assessed the in vitro activity of the boronic acid-based ß-lactamase inhibitor, vaborbactam, with different ß-lactams against 100 clinical MAB isolates. Enhanced activity was observed with meropenem and ceftaroline with vaborbactam (1- and >4-fold MIC50/90 reduction). CRISPRi-mediated blaMAB gene knockdown showed a fourfold MIC reduction to ceftaroline but not the other ß-lactams. Our findings demonstrate vaborbactam's potential in combination therapy against MAB infections.

Comprehensive stability analysis of 13 ß-lactams and ß-lactamase inhibitors in in vitro media, and novel supplement dosing strategy to mitigate thermal drug degradation.

Non-clinical antibiotic development relies on in vitro susceptibility and infection model studies. Validating the achievement of the targeted drug concentrations is essential to avoid under-estimation of drug effects and over-estimation of resistance emergence. While certain ß-lactams (e.g., imipenem) and ß-lactamase inhibitors (BLIs; clavulanic acid) are believed to be relatively unstable, limited tangible data on their stability in commonly used in vitro media are known. We aimed to determine the thermal stability of 10 ß-lactams and 3 BLIs via LC-MS/MS in cation-adjusted Mueller Hinton broth at 25 and 36°C as well as agar at 4 and 37°C, and in water at -20, 4, and 25°C. Supplement dosing algorithms were developed to achieve broth concentrations close to their target over 24 h. During incubation in broth (pH 7.25)/agar, degradation half-lives were 16.9/21.8 h for imipenem, 20.7/31.6 h for biapenem, 29.0 h for clavulanic acid (studied in broth only), 23.1/71.6 h for cefsulodin, 40.6/57.9 h for doripenem, 46.5/64.6 h for meropenem, 50.8/97.7 h for cefepime, 61.5/99.5 h for piperacillin, and >120 h for all other compounds. Broth stability decreased at higher pH. All drugs were ≥90% stable for 72 h in agar at 4°C. Degradation half-lives in water at 25°C were >200 h for all drugs except imipenem (14.7 h, at 1,000 mg/L) and doripenem (59.5 h). One imipenem supplement dose allowed concentrations to stay within ±31% of their target concentration. This study provides comprehensive stability data on ß-lactams and BLIs in relevant in vitro media using LC-MS/MS. Future studies are warranted applying these data to antimicrobial susceptibility testing and assessing the impact of ß-lactamase-related degradation.

In vitro activity of sulbactam-durlobactam against colistin-resistant and/or cefiderocol-non-susceptible, carbapenem-resistant Acinetobacter baumannii collected in U.S. hospitals.

The activity of a novel ß-lactamase inhibitor combination, sulbactam-durlobactam (SUL-DUR), was tested against 87 colistin-resistant and/or cefiderocol-non-susceptible carbapenem-resistant Acinetobacter baumannii clinical isolates collected from U.S. hospitals between 2017 and 2019. Among them, 89% and 97% were susceptible to SUL-DUR and imipenem plus SUL-DUR, with MIC50/MIC90 values of 2 µg/mL/8 µg/mL and 1 µg/mL/4 µg/mL, respectively. The presence of amino acid substitutions in penicillin-binding protein 3, including previously reported A515V or T526S, was associated with SUL-DUR non-susceptibility.

An optimized cyclophosphamide-treated mouse model of Mycobacterium abscessus pulmonary infection.

Mycobacterium abscessus pulmonary infections are increasingly problematic, especially for immunocompromised individuals and those with underlying lung conditions. Currently, there is no reliable standardized treatment, underscoring the need for improved preclinical drug testing. We present a simplified immunosuppressed mouse model using only four injections of cyclophosphamide, which allows for sustained M. abscessus lung burden for up to 16 days. This model proved effective for antibiotic efficacy evaluation, as demonstrated with imipenem or amikacin.

Understanding blaNDM-1 gene regulation in CRKP infections: toward novel antimicrobial strategies for hospital-acquired pneumonia.

BACKGROUND: The escalating challenge of Carbapenem-resistant Klebsiella pneumoniae (CRKP) in hospital-acquired pneumonia (HAP) is closely linked to the blaNDM-1 gene. This study explores the regulatory mechanisms of blaNDM-1 expression and aims to enhance antibacterial tactics to counteract the spread and infection of resistant bacteria. METHODS: KP and CRKP strains were isolated from HAP patients' blood samples. Transcriptomic sequencing (RNA-seq) identified significant upregulation of blaNDM-1 gene expression in CRKP strains. Bioinformatics analysis revealed blaNDM-1 gene involvement in beta-lactam resistance pathways. CRISPR-Cas9 was used to delete the blaNDM-1 gene, restoring sensitivity. In vitro and in vivo experiments demonstrated enhanced efficacy with Imipenem and Thanatin or Subatan combination therapy. RESULTS: KP and CRKP strains were isolated with significant upregulation of blaNDM-1 in CRKP strains identified by RNA-seq. The Beta-lactam resistance pathway was implicated in bioinformatics analysis. Knockout of blaNDM-1 reinstated sensitivity in CRKP strains. Further, co-treatment with Imipenem, Thanatin, or Subactam markedly improved antimicrobial effectiveness. CONCLUSION: Silencing blaNDM-1 in CRKP strains from HAP patients weakens their Carbapenem resistance and optimizes antibacterial strategies. These results provide new theoretical insights and practical methods for treating resistant bacterial infections.

Rhodococcus infection: a 10-year retrospective analysis of clinical experience and antimicrobial susceptibility profile.

Rhodococcus equi is an opportunistic pathogen known to cause pulmonary and extrapulmonary disease among immunocompromised patients. Treatment is frequently challenging due to intrinsic resistance to multiple antibiotic classes. While non-equi Rhodococcus spp. are prevalent, their clinical significance is poorly defined. There is also limited data on antibiotic susceptibility testing (AST) of Rhodococcus infection in humans. We conducted a single-center, retrospective cohort study evaluating clinical characteristics, microbiologic profile, and AST of Rhodococcus infections between June 2012 and 2022 at our tertiary academic medical center. Identification of Rhodococcus spp. was performed by Sanger 16S rRNA gene sequencing and/or matrix-assisted laser desorption ionization-time of flight mass spectrometry, and AST was performed by agar dilution. Three hundred twenty-two isolates of Rhodococcus spp. were identified from blood (50%), pulmonary (26%), and bone/joint (12%) sources. R. equi/hoagii, R. corynebacterioides, and R. erythropolis were the most frequently isolated species, with 19% of isolates identified only to genus level. One hundred ninety-nine isolates evaluated for AST demonstrated high-level resistance to amoxicillin/clavulanate, cephalosporins, and aminoglycosides. More than 95% susceptibility to imipenem, vancomycin, linezolid, rifampin, and clarithromycin was observed. Non-equi species showed a significantly more favorable AST profile relative to R. equi. Clinically significant Rhodococcus infection was rare with 10 cases diagnosed (majority due to R. equi) and managed. The majority of patients received 2- or 3-drug combination therapy for 2-6 months, with favorable clinical response. Significant differences in AST were observed between R. equi and non-equi species. Despite high antimicrobial resistance to several antibiotic classes, imipenem and vancomycin remain appropriate empiric treatment options for R. equi. Future research evaluating mechanisms underlying antimicrobial resistance is warranted.

Improved Blue Carba test and Carba NP test for detection and classification of major Class A and B carbapenemases, including dual producers, among Gram-negative bacilli.

Prompt and precise identification of carbapenemase-producing organisms is crucial for guiding clinical antibiotic treatments and limiting transmission. Here, we propose modifying the Blue Carba test (BCT) and Carba NP-direct (CNPd) to identify molecular carbapenemase classes, including dual carbapenemase strains, by adding specific Class A and Class B inhibitors. We tested 171 carbapenemase-producing Gram-negative bacilli strains-21 in Class A (KPC, NMC, SME), 58 in Class B (IMP, VIM, NDM, SPM), and 92 with dual carbapenemase production (KPC+NDM, KPC+IMP, KPC+VIM), all previously positive with BCT or CNPd. We also included 13 carbapenemase non-producers. ß-lactamases were previously characterized by PCR. The improved BCT/CNPd methods detect imipenem hydrolysis from an imipenem-cilastatin solution, using pH indicators and Class A (avibactam) and/or Class B (EDTA) inhibitors. Results were interpreted visually based on color changes. CNPd achieved 99.4% sensitivity and 100% specificity in categorizing carbapenemases, while BCT had 91.8% sensitivity and 100% specificity. Performance varied by carbapenemase classes: both tests classified all Class A-producing strains. For Class B, the CNP test identified 57/58 strains (98.3%), whereas the BCT test, 45/58 strains (77.6%), with non-fermenters posing the greatest detection challenge. For Classes A plus B dual producers, both tests performed exceptionally well, with only one indeterminate strain for the BCT. The statistical comparison showed both methods had similar times to a positive result, with differences based on the carbapenemase class or bacterial group involved. This improved assay rapidly distinguishes major Class A or Class B carbapenemase producers among Gram-negative bacilli, including dual-class combinations, in less than 2 hours. IMPORTANCE: Rapid and accurate identification of carbapenemase-producing organisms is of vital importance in guiding appropriate clinical antibiotic treatments and curbing their transmission. The emergence of negative bacilli carrying multiple carbapenemase combinations during and after the severe acute respiratory syndrome coronavirus 2 pandemic has posed a challenge to the conventional biochemical tests typically used to determine the specific carbapenemase type in the isolated strains. Several initiatives have aimed to enhance colorimetric methods, enabling them to independently identify the presence of Class A or Class B carbapenemases. Notably, no previous efforts have been made to distinguish both classes simultaneously. Additionally, these modifications have struggled to differentiate between carriers of multiple carbapenemases, a common occurrence in many Latin American countries. In this study, we introduced specific Class A and Class B carbapenemase inhibitors into the Blue Carba test (BCT) and Carba NP-direct (CNP) colorimetric assays to identify the type of carbapenemase, even in cases of multiple carbapenemase producers within these classes. These updated assays demonstrated exceptional sensitivity and specificity (≥ 90%) all within a rapid turnaround time of under 2 hours, typically completed in just 45 minutes. These in-house enhancements to the BCT and CNP assays present a rapid, straightforward, and cost-effective approach to determining the primary carbapenemase classes. They could serve as a viable alternative to molecular biology or immuno-chromatography techniques, acting as an initial diagnostic step in the process.

Imipenem/relebactam pharmacokinetics in critically ill patients supported on extracorporeal membrane oxygenation.

BACKGROUND: Extracorporeal membrane oxygenation (ECMO) is a life-saving modality but has the potential to alter the pharmacokinetics (PK) of antimicrobials. Imipenem/cilastatin/relebactam is an antibiotic with utility in treating certain multi-drug resistant Gram-negative infections. Herein, we describe the population pharmacokinetics of imipenem and relebactam in critically ill patients supported on ECMO. METHODS: Patients with infection supported on ECMO received 4-6 doses of imipenem/cilastatin/relebactam per current prescribing information based on estimated creatinine clearance. Blood samples were collected following the final dose of the antibiotic. Concentrations were determined via LC-MS/MS. Population PK models were fit with and without covariates using Pmetrics. Monte Carlo simulations of 1000 patients assessed joint PTA of fAUC0-24/MIC ≥ 8 for relebactam, and ≥40% fT > MIC for imipenem for each approved dosing regimen. RESULTS: Seven patients supported on ECMO were included in PK analyses. A two-compartment model with creatinine clearance as a covariate on clearance for both imipenem and relebactam fitted the data best. The mean ±â€Šstandard deviation parameters were: CL0, 15.21 ±â€Š6.52 L/h; Vc, 10.13 ±â€Š2.26 L; K12, 2.45 ±â€Š1.16 h-1 and K21, 1.76 ±â€Š0.49 h-1 for imipenem, and 6.95 ±â€Š1.34 L/h, 9.81 ±â€Š2.69 L, 2.43 ±â€Š1.13 h-1 and 1.52 ±â€Š0.67 h-1 for relebactam. Simulating each approved dose of imipenem/cilastatin/relebactam according to creatinine clearance yielded PTAs of ≥90% up to an MIC of 2 mg/L. CONCLUSIONS: Imipenem/cilastatin/relebactam dosed according to package insert in patients supported on ECMO is predicted to achieve exposures sufficient to treat susceptible Gram-negative isolates, including Pseudomonas aeruginosa.

Imipenem reduces the efficacy of vancomycin against Elizabethkingia species.

BACKGROUND: Elizabethkingia spp. are emerging as nosocomial pathogens causing various infections. These pathogens express resistance to a broad range of antibiotics, thus requiring antimicrobial combinations for coverage. However, possible antagonistic interactions between antibiotics have not been thoroughly explored. This study aimed to evaluate the effectiveness of antimicrobial combinations against Elizabethkingia infections, focusing on their impact on pathogenicity, including biofilm production and cell adhesion. METHODS: Double-disc diffusion, time-kill, and chequerboard assays were used for evaluating the combination effects of antibiotics against Elizabethkingia spp. We further examined the antagonistic effects of antibiotic combinations on biofilm formation and adherence to A549 human respiratory epithelial cells. Further validation of the antibiotic interactions and their implications was performed using ex vivo hamster precision-cut lung sections (PCLSs) to mimic in vivo conditions. RESULTS: Antagonistic effects were observed between cefoxitin, imipenem and amoxicillin/clavulanic acid in combination with vancomycin. The antagonism of imipenem toward vancomycin was specific to its effects on the genus Elizabethkingia. Imipenem further hampered the bactericidal effect of vancomycin and impaired its inhibition of biofilm formation and the adhesion of Elizabethkingia meningoseptica ATCC 13253 to human cells. In the ex vivo PCLS model, vancomycin exhibited dose-dependent bactericidal effects; however, the addition of imipenem also reduced the effect of vancomycin. CONCLUSIONS: Imipenem reduced the bactericidal efficacy of vancomycin against Elizabethkingia spp. and compromised its capacity to inhibit biofilm formation, thereby enhancing bacterial adhesion. Clinicians should be aware of the potential issues with the use of these antibiotic combinations when treating Elizabethkingia infections.

Assessing the in vivo impact of novel ß-lactamase inhibitors on the efficacy of their partner ß-lactams against serine carbapenemase-producing Pseudomonas aeruginosa using human-simulated exposures.

OBJECTIVES: To evaluate the efficacy of human-simulated regimens (HSRs) of ceftazidime, ceftazidime/avibactam, imipenem, imipenem/relebactam, meropenem and meropenem/vaborbactam in a murine thigh infection model against serine carbapenemase-producing Pseudomonas aeruginosa. METHODS: Nine P. aeruginosa clinical isolates harbouring GES-5 (n = 1), GES-20 (n = 1), GES-5/20 (n = 1), GES-19, GES-20 (n = 3) and KPC (n = 3) were evaluated. Six mice were administered HSRs of ceftazidime 2 g q8h (2 h infusion), ceftazidime/avibactam 2.5 g q8h (2 h infusion), meropenem 2 g q8h (3 h infusion), imipenem 0.5 g q6h (0.5 h infusion), imipenem/relebactam 1.25 g q6h (0.5 h infusion) and meropenem/vaborbactam 4 g q8h (3 h infusion). Change in bacterial burden relative to baseline and the percent of isolates meeting the 1 log10 kill endpoint were assessed. RESULTS: The addition of avibactam to ceftazidime increased the percentage of isolates meeting 1 log10 kill from 33% to 100% of GES- or KPC-harbouring isolates. Imipenem/relebactam HSR produced ≥1 log10 of kill against 83% and 100% of GES- and KPC-harbouring isolates, respectively, while imipenem alone failed to reach 1 log10 kill for any isolates. Vaborbactam resulted in variable restoration of meropenem activity as 1 log10 kill was achieved in only 33% and 66% of GES- and KPC-harbouring isolates, respectively, compared with no isolates for meropenem alone. CONCLUSIONS: Ceftazidime/avibactam and imipenem/relebactam were active against 100% and 89% of KPC- or GES-harbouring isolates tested in vivo. The activity of meropenem/vaborbactam was variable, suggesting this may be an inferior treatment option in this setting. Further studies to evaluate clinical outcomes in GES- and KPC-producing P. aeruginosa are warranted given their increasing prevalence worldwide.

Antimicrobial susceptibility profile of clinically relevant Bacteroides, Phocaeicola, Parabacteroides and Prevotella species, isolated by eight laboratories in the Netherlands.

OBJECTIVES: Recently, reports on antimicrobial-resistant Bacteroides and Prevotella isolates have increased in the Netherlands. This urged the need for a surveillance study on the antimicrobial susceptibility profile of Bacteroides, Phocaeicola, Parabacteroides and Prevotella isolates consecutively isolated from human clinical specimens at eight different Dutch laboratories. METHODS: Each laboratory collected 20-25 Bacteroides (including Phocaeicola and Parabacteroides) and 10-15 Prevotella isolates for 3 months. At the national reference laboratory, the MICs of amoxicillin, amoxicillin/clavulanic acid, piperacillin/tazobactam, meropenem, imipenem, metronidazole, clindamycin, tetracycline and moxifloxacin were determined using agar dilution. Isolates with a high MIC of metronidazole or a carbapenem, or harbouring cfiA, were subjected to WGS. RESULTS: Bacteroides thetaiotaomicron/faecis isolates had the highest MIC90 values, whereas Bacteroides fragilis had the lowest MIC90 values for amoxicillin/clavulanic acid, piperacillin/tazobactam, meropenem, imipenem and moxifloxacin. The antimicrobial profiles of the different Prevotella species were similar, except for amoxicillin, for which the MIC50 ranged from 0.125 to 16 mg/L for Prevotella bivia and Prevotella buccae, respectively. Three isolates with high metronidazole MICs were sequenced, of which one Bacteroides thetaiotaomicron isolate harboured a plasmid-located nimE gene and a Prevotella melaninogenica isolate harboured a nimA gene chromosomally.Five Bacteroides isolates harboured a cfiA gene and three had an IS element upstream, resulting in high MICs of carbapenems. The other two isolates harboured no IS element upstream of the cfiA gene and had low MICs of carbapenems. CONCLUSIONS: Variations in resistance between species were observed. To combat emerging resistance in anaerobes, monitoring resistance and conducting surveillance are essential.

Regulation of overexpressed efflux pump encoding genes by cinnamon oil and trimethoprim to abolish carbapenem-resistant Acinetobacter baumannii clinical strains.

Resistance mechanisms are a shelter for Acinetobacter baumannii to adapt to our environment which causes difficulty for the infections to be treated and WHO declares this organism on the top of pathogens priority for new drug development. The most common mechanism that develops drug resistance is the overexpression of the efflux pump, especially Resistance-nodulation-cell division (RND) family, to almost most antibiotics. The study is designed to detect RND efflux pump genes in A. baumannii, and its correlation to multidrug resistance, in particular, the carbapenems resistance Acinetobacter baumannii (CRAB), and using different inhibitors that restore the antibiotic susceptibility of imipenem. Clinical A. baumannii isolates were recovered from different Egyptian hospitals in Intensive care unit (ICU). The expression of genes in two strains was analyzed using RT-PCR before and after inhibitor treatment. About 100 clinical A. baumannii isolates were recovered and identified and recorded as MDR strains with 75% strains resistant to imipenem. adeB, adeC, adeK, and adeJ were detected in thirty- seven the carbapenems resistance Acinetobacter baumannii (CRAB) strains. Cinnamomum verum oil, Trimethoprim, and Omeprazole was promising inhibitor against 90% of the carbapenems resistance Acinetobacter baumannii (CRAB) strains with a 2-6-fold decrease in imipenem MIC. Downregulation of four genes was associated with the addition of those inhibitors to imipenem for two the carbapenems resistance Acinetobacter baumannii (CRAB) (ACN15 and ACN99) strains, and the effect was confirmed in 24 h killing kinetics. Our investigation points to the carbapenems resistance Acinetobacter baumannii (CRAB) strain's prevalence in Egyptian hospitals with the idea to revive the imipenem activity using natural and chemical drugs as inhibitors that possessed high synergistic activity.

Based on molecular docking and real-time PCR technology, the two-component system Bae SR was investigated on the mechanism of drug resistance in CRAB.

This study aimed to explore the role of the two-component system Bae SR in the mechanism of drug resistance in carbapenem-resistant A. baumannii (CRAB) using molecular docking and real-time polymerase chain reaction (PCR). The two-component system Bae SR of Acinetobacter baumannii was subjected to molecular docking with imipenem, meropenem, and levofloxacin. Antibacterial assays and fluorescence quantitative PCR were used to explore protein-ligand interactions and molecular biological resistance mechanisms related to CRAB. The analysis of the two-component system in A. baumannii revealed that imipenem exhibited the highest docking energy in Bae S at - 5.81 kcal/mol, while the docking energy for meropenem was - 4.92 kcal/mol. For Bae R, imipenem had a maximum docking energy of - 4.28 kcal/mol, compared with - 4.60 kcal/mol for meropenem. The highest binding energies for Bae S-levofloxacin and Bae R-levofloxacin were - 3.60 and - 3.65 kcal/mol, respectively. All imipenem-resistant strains had minimum inhibitory concentration (MIC) values of 16 µg/mL, whereas levofloxacin-resistant strains had MIC values of 8 µg/mL. The time-sterilization curve showed a significant decrease in bacterial colony numbers at 2 h under the action of 8 µg/mL imipenem, indicating antibacterial effects. In contrast, levofloxacin did not exhibit any antibacterial activity. Fluorescence quantitative PCR results revealed significantly increased relative expression levels of bae S and bae R genes in the CRAB group, which were 2 and 1.5 times higher than those in the CSAB group, respectively, with statistically significant differences. Molecular docking in this study found that the combination of Bae SR and carbapenem antibiotics (imipenem, meropenem) exhibited stronger affinity and stability compared with levofloxacin. Moreover, the overexpression of the two-component system genes in carbapenem-resistant A. baumannii enhanced its resistance to carbapenem, providing theoretical and practical insights into carbapenem resistance in respiratory tract infections caused by A. baumannii.

Characterization of genes related to the efflux pump and porin in multidrug-resistant Escherichia coli strains isolated from patients with COVID-19 after secondary infection.

BACKGROUND: Escherichia coli (E. coli) is a multidrug resistant opportunistic pathogen that can cause secondary bacterial infections in patients with COVID-19. This study aimed to determine the antimicrobial resistance profile of E. coli as a secondary bacterial infection in patients with COVID-19 and to assess the prevalence and characterization of genes related to efflux pumps and porin. METHODS: A total of 50 nonduplicate E. coli isolates were collected as secondary bacterial infections in COVID-19 patients. The isolates were cultured from sputum samples. Confirmation and antibiotic susceptibility testing were conducted by Vitek 2. PCR was used to assess the prevalence of the efflux pump and porin-related genes in the isolates. The phenotypic and genotypic evolution of antibiotic resistance genes related to the efflux pump was evaluated. RESULTS: The E. coli isolates demonstrated high resistance to ampicillin (100%), cefixime (62%), cefepime (62%), amoxicillin-clavulanic acid (60%), cefuroxime (60%), and ceftriaxone (58%). The susceptibility of E. coli to ertapenem was greatest (92%), followed by imipenem (88%), meropenem (86%), tigecycline (80%), and levofloxacin (76%). Regarding efflux pump gene combinations, there was a significant association between the acrA gene and increased resistance to levofloxacin, between the acrB gene and decreased resistance to meropenem and increased resistance to levofloxacin, and between the ompF and ompC genes and increased resistance to gentamicin. CONCLUSIONS: The antibiotics ertapenem, imipenem, meropenem, tigecycline, and levofloxacin were effective against E. coli in patients with COVID-19. Genes encoding efflux pumps and porins, such as acrA, acrB, and outer membrane porins, were highly distributed among all the isolates. Efflux pump inhibitors could be alternative antibiotics for restoring tetracycline activity in E. coli isolates.

Sub-inhibitory concentrations of colistin and imipenem impact the expression of biofilm-associated genes in Acinetobacter baumannii.

Acinetobacter baumannii is an opportunistic pathogen that is responsible for nosocomial infections. Imipenem and colistin are drugs that are commonly used to treat severe infections caused by A. baumannii, such as sepsis, ventilator-associated pneumonia, and bacteremia. However, some strains of A. baumannii have become resistant to these drugs, which is a concern for public health. Biofilms produced by A. baumannii increase their resistance to antibiotics and the cells within the inner layers of biofilm are exposed to sub-inhibitory concentrations (sub-MICs) of antibiotics. There is limited information available regarding how the genes of A. baumannii are linked to biofilm formation when the bacteria are exposed to sub-MICs of imipenem and colistin. Thus, this study's objective was to explore this relationship by examining the genes involved in biofilm formation in A. baumannii when exposed to low levels of imipenem and colistin. The study found that exposing an isolate of A. baumannii to low levels of these drugs caused changes in their drug susceptibility pattern. The relative gene expression profiles of the biofilm-associated genes exhibited a change in their expression profile during short-term and long-term exposure. This study highlights the potential consequences of overuse and misuse of antibiotics, which can help bacteria become resistant to these drugs.

Activity of imipenem/relebactam and comparators against KPC-producing Klebsiella pneumoniae and imipenem-resistant Pseudomonas aeruginosa.

PURPOSE: Relebactam is a novel ß-lactamase inhibitor, which, when combined with imipenem/cilastatin, is active against both class A and class C ß-lactamases. To evaluate in vitro antimicrobial activity of imipenem/relebactam against a collection of recent clinical isolates of carbapenem-non-susceptible P. aeruginosa and K. pneumoniae ST258 and ST512 KPC producers belonging to different lineages from hospitals in Southern Spain. METHODS: Six hundred and seventy-eight isolates were tested: 265 K. pneumoniae (230 ST512/KPC-3 and 35 ST258/KPC-3) and 413 carbapenem-non-susceptible P. aeruginosa. Imipenem, piperacillin/tazobactam, ceftazidime, cefepime, aztreonam, ceftolozane/tazobactam, meropenem, amikacin, ciprofloxacin, colistin, and ceftazidime/avibactam were used as comparators against P. aeruginosa. Against K. pneumoniae ceftazidime, cefepime, aztreonam, and ceftolozane/tazobactam were not tested, and tigecycline was studied instead. MICs were determined in duplicate by broth microdilution according to EUCAST guidelines. RESULTS: Imipenem/relebactam displayed potent in vitro activity against both sequence types of KPC-3-producing K. pneumoniae. MIC50 and MIC90 values were 0.25 mg/L and 1 mg/L, respectively, with percent of susceptible isolates >97%. Only three K. pneumoniae ST512/KPC-3 isolates and one ST258/KPC-3 were resistant to imipenem/relebactam. Relebactam sensitized 98.5% of K. pneumoniae isolates resistant to imipenem. The activity of imipenem/relebactam against P. aeruginosa was moderate (susceptibility rate: 62.7%). Analysis of the acquired and mutational resistome of isolates with high levels of resistance to imipenem/relebactam has not shown a clear association between them. CONCLUSION: Imipenem/relebactam showed excellent activity against K. pneumoniae KPC-3. The activity of imipenem/relebactam against imipenem-resistant P. aeruginosa was moderate.

Activity of ceftolozane/tazobactam and imipenem/relebactam against clinical isolates of Enterobacterales and Pseudomonas aeruginosa collected in Greece and Italy-SMART 2017-2021.

PURPOSE: The current study evaluated the in vitro activities of ceftolozane/tazobactam (C/T), imipenem/relebactam (IMI/REL), and comparators against recent (2017-2021) clinical isolates of gram-negative bacilli from two countries in southern Europe. METHODS: Nine clinical laboratories (two in Greece; seven in Italy) each collected up to 250 consecutive gram-negative isolates per year from lower respiratory tract, intraabdominal, urinary tract, and bloodstream infection samples. MICs were determined by the CLSI broth microdilution method and interpreted using 2022 EUCAST breakpoints. ß-lactamase genes were identified in select ß-lactam-nonsusceptible isolate subsets. RESULTS: C/T inhibited the growth of 85-87% of Enterobacterales and 94-96% of ESBL-positive non-CRE NME (non-Morganellaceae Enterobacterales) isolates from both countries. IMI/REL inhibited 95-98% of NME, 100% of ESBL-positive non-CRE NME, and 98-99% of KPC-positive NME isolates from both countries. Country-specific differences in percent susceptible values for C/T, IMI/REL, meropenem, piperacillin/tazobactam, levofloxacin, and amikacin were more pronounced for Pseudomonas aeruginosa than Enterobacterales. C/T and IMI/REL both inhibited 84% of P. aeruginosa isolates from Greece and 91-92% of isolates from Italy. MBL rates were estimated as 4% of Enterobacterales and 10% of P. aeruginosa isolates from Greece compared to 1% of Enterobacterales and 3% of P. aeruginosa isolates from Italy. KPC rates among Enterobacterales isolates were similar in both countries (7-8%). OXA-48-like enzymes were only identified in Enterobacterales isolates from Italy (1%) while GES carbapenemase genes were only identified in P. aeruginosa isolates from Italy (2%). CONCLUSION: We conclude that C/T and IMI/REL may provide viable treatment options for many patients from Greece and Italy.

Multidrug-resistant Gram-negative clinical isolates with reduced susceptibility/resistance to cefiderocol: which are the best present and future therapeutic alternatives?

PURPOSE: To evaluate the different present and future therapeutic ß-lactam/ß-lactamase inhibitor (BL/BLI) alternatives, namely aztreonam-avibactam, imipenem-relebactam, meropenem-vaborbactam, cefepime-zidebactam, cefepime-taniborbactam, meropenem-nacubactam, and sulbactam-durlobactam against clinical isolates showing reduced susceptibility or resistance to cefiderocol in Enterobacterales, Acinetobacter baumannii, and Pseudomonas aeruginosa. METHODS: MIC values of aztreonam, aztreonam-avibactam, cefepime, cefepime-taniborbactam, cefepime-zidebactam, imipenem, imipenem-relebactam, meropenem, meropenem-vaborbactam, meropenem-nacubactam, sulbactam-durlobactam, and cefiderocol combined with a BLI were determined for 67, 9, and 11 clinical Enterobacterales, P. aeruginosa or A. baumannii isolates, respectively, showing MIC values of cefiderocol being ≥1 mg/L. If unavailable, the respective ß-lactam breakpoints according to EUCAST were used for BL/BLI combinations. RESULTS: For Enterobacterales, the susceptibility rates for aztreonam, cefepime, imipenem, and meropenem were 7.5%, 0%, 10.4%, and 10.4%, respectively, while they were much higher for cefepime-zidebactam (91%), cefiderocol-zidebactam (91%), meropenem-nacubactam (71.6%), cefiderocol-nacubactam (74.6%), and cefiderocol-taniborbactam (76.1%), as expected. For P. aeruginosa isolates, the higher susceptibility rates were observed for imipenem-relebactam, cefiderocol-zidebactam, and meropenem-vaborbactam (56% for all combinations). For A. baumannii isolates, lower susceptibility rates were observed with commercially or under development BL/BLI combos; however, a high susceptibility rate (70%) was found for sulbactam-durlobactam and when cefiderocol was associated to some BLIs. CONCLUSIONS: Zidebactam- and nacubactam-containing combinations showed a significant in vitro activity against multidrug-resistant Enterobacterales clinical isolates with reduced susceptibility to cefiderocol. On the other hand, imipenem-relebactam and meropenem-vaborbactam showed the highest susceptibility rates against P. aeruginosa isolates. Finally, sulbactam-durlobactam and cefiderocol combined with a BLI were the only effective options against A. baumannii tested isolates.