Activity of cefepime/zidebactam against MDR Escherichia coli isolates harbouring a novel mechanism of resistance based on four-amino-acid inserts in PBP3.

BACKGROUND: Recent reports reveal the emergence of Escherichia coli isolates harbouring a novel resistance mechanism based on four-amino-acid inserts in PBP3. These organisms concomitantly expressed ESBLs or/and serine-/metallo-carbapenemases and were phenotypically detected by elevated aztreonam/avibactam MICs. OBJECTIVES: The in vitro activities of the investigational antibiotic cefepime/zidebactam and approved antibiotics (ceftazidime/avibactam, ceftolozane/tazobactam, imipenem/relebactam and others) were determined against E. coli isolates harbouring four-amino-acid inserts in PBP3. METHODS: Whole-genome sequenced E. coli isolates (n = 89) collected from a large tertiary care hospital in Southern India (n = 64) and from 12 tertiary care hospitals located across India (n = 25) during 2016-18, showing aztreonam/avibactam MICs ≥1 mg/L (≥4 times the aztreonam epidemiological cut-off) were included in this study. The MICs of antibiotics were determined using the reference broth microdilution method. RESULTS: Four-amino-acid inserts [YRIK (n = 30) and YRIN (n = 53)] were found in 83/89 isolates. Among 83 isolates, 65 carried carbapenemase genes [blaNDM (n = 39), blaOXA-48-like (n = 11) and blaNDM + blaOXA-48-like (n = 15)] and 18 isolates produced ESBLs/class C ß-lactamases only. At least 16 unique STs were noted. Cefepime/zidebactam demonstrated potent activity, with all isolates inhibited at ≤1 mg/L. Comparator antibiotics including ceftazidime/avibactam and imipenem/relebactam showed limited activities. CONCLUSIONS: E. coli isolates concurrently harbouring four-amino-acid inserts in PBP3 and NDM are an emerging therapeutic challenge. Assisted by the PBP2-binding action of zidebactam, the cefepime/zidebactam combination overcomes both target modification (PBP3 insert)- and carbapenemase (NDM)-mediated resistance mechanisms in E. coli.

Transcending the challenge of evolving resistance mechanisms in Pseudomonas aeruginosa through ß-lactam-enhancer-mechanism-based cefepime/zidebactam.

Multi-drug resistant (MDR) Pseudomonas aeruginosa harbor a complex array of ß-lactamases and non-enzymatic resistance mechanisms. In this study, the activity of a ß-lactam/ß-lactam-enhancer, cefepime/zidebactam, and novel ß-lactam/ß-lactamase inhibitor combinations was determined against an MDR phenotype-enriched, challenge panel of P. aeruginosa (n = 108). Isolates were multi-clonal as they belonged to at least 29 distinct sequence types (STs) and harbored metallo-ß-lactamases, serine ß-lactamases, penicillin binding protein (PBP) mutations, and other non-enzymatic resistance mechanisms. Ceftazidime/avibactam, ceftolozane/tazobactam, imipenem/relebactam, and cefepime/taniborbactam demonstrated MIC90s of >128 mg/L, while cefepime/zidebactam MIC90 was 16 mg/L. In a neutropenic-murine lung infection model, a cefepime/zidebactam human epithelial-lining fluid-simulated regimen achieved or exceeded a translational end point of 1-log10 kill for the isolates with elevated cefepime/zidebactam MICs (16-32 mg/L), harboring VIM-2 or KPC-2 and alterations in PBP2 and PBP3. In the same model, to assess the impact of zidebactam on the pharmacodynamic (PD) requirement of cefepime, dose-fractionation studies were undertaken employing cefepime-susceptible P. aeruginosa isolates. Administered alone, cefepime required 47%-68% fT >MIC for stasis to ~1 log10 kill effect, while cefepime in the presence of zidebactam required just 8%-16% for >2 log10 kill effect, thus, providing the pharmacokinetic/PD basis for in vivo efficacy of cefepime/zidebactam against isolates with MICs up to 32 mg/L. Unlike ß-lactam/ß-lactamase inhibitors, ß-lactam enhancer mechanism-based cefepime/zidebactam shows a potential to transcend the challenge of ever-evolving resistance mechanisms by targeting multiple PBPs and overcoming diverse ß-lactamases including carbapenemases in P. aeruginosa.IMPORTANCECompared to other genera of Gram-negative pathogens, Pseudomonas is adept in acquiring complex non-enzymatic and enzymatic resistance mechanisms thus remaining a challenge to even novel antibiotics including recently developed ß-lactam and ß-lactamase inhibitor combinations. This study shows that the novel ß-lactam enhancer approach enables cefepime/zidebactam to overcome both non-enzymatic and enzymatic resistance mechanisms associated with a challenging panel of P. aeruginosa. This study highlights that the ß-lactam enhancer mechanism is a promising alternative to the conventional ß-lactam/ß-lactamase inhibitor approach in combating ever-evolving MDR P. aeruginosa.

In vitro activity of cefepime/zidebactam (WCK 5222) against recent Gram-negative isolates collected from high resistance settings of Greek hospitals.

Cefepime/zidebactam is in clinical development for the treatment of carbapenem-resistant Gram-negative infections. MICs of cefepime/zidebactam (1:1) and comparators against Enterobacterales (n = 563), Pseudomonas (n = 172) and Acinetobacter baumannii (n =181) collected from 15 Greek hospitals (2014-2018) were determined by reference broth microdilution method. The isolates exhibited high carbapenem resistance rates [(Enterobacterales (75%), Pseudomonas (75%) and A. baumannii (98.3%)]. Cefepime/zidebactam showed MIC50/90 of 0.5/2 mg/L, against Enterobacterales including metallo-ß-lactamases (MBL)-producers. Reduced susceptibility rates to tigecycline (16.8%), colistin (47.4%), ceftazidime/avibactam (59.8%), and imipenem/relebactam (61%) indicated high prevalence of multi-drug resistance among Greek Enterobacterales. Cefepime/zidebactam exhibited MIC50/90 of 8/16 mg/L against Pseudomonas including MBL-producers. The MIC50/90 of ceftazidime/avibactam and imipenem/relebactam were high (≥32 mg/L). Cefepime/zidebactam showed MIC90 of 64 mg/L against A. baumannii which is within its therapeutic scope. Other antibiotics including colistin showed limited activity against A. baumannii. The activity of cefepime/zidebactam against multi-drug-resistant isolates is attributable to zidebactam mediated novel ß-lactam-enhancer mechanism.