RESUMO
BACKGROUND: There is a high diversity of beta-lactamases in gram negative pathogens, making them difficult to treat. In the presence of OXA-1 and ampC, PTZ is no longer clinically relevant when treating Enterobacterales expressing ESBLs. Further, MBL infections are often treated with the combination of ceftazidime/avibactam with aztreonam. . It has recently been reported that NDM-expressing E. coli isolates co-harboring PBP3 insert develops resistance to this triple combination. METHODS: A pentaplex PCR is developed and validated to simultaneously detect blaCTX-M, blaOXA-1, blaCMY, blaNDM, and the PBP3 insert in whole genome sequenced E. coli and K. pneumoniae isolates. In addition, the isolates chosen for pentaplex PCR evaluation were tested for their minimum inhibitory concentrations (MICs) against piperacillin/tazobactam, cefoperazone/sulbactam (C/S), ertapenem, imipenem, meropenem, ceftazidime/avibactam, aztreonam/avibactam, cefepime/taniborbactam, and cefiderocol. RESULTS: The developed pentaplex PCR showed 100 % reproducibility with the antimicrobial resistance profile generated from whole genome sequenced data. PTZ and C/S are not effective against ESBL and/or OXA-1 expressing E. coli and K. pneumoniae isolates and do not offer any activity against CMY co-producers. Further, the combined effect of CMY, NDM and PBP3 inserts impacts aztreonam/avibactam activity and reduces the susceptibility to 40 % in E. coli isolates. While, aztreonam/avibactam showed potent activity against NDM-expressing K. pneumoniae isolates. Importantly, cefepime/taniborbactam and cefiderocol showed limited activity against NDM-expressing E. coli and K. pneumoniae isolates. CONCLUSION: The pentaplex PCR was effective in detecting four beta-lactamases (blaCTX-M, blaOXA-1, blaCMY, blaNDM) as well as PBP3 inserts. It is expected that using pentaplex PCR as a diagnostic test for resistance detection in clinical practice will improve patient outcomes by providing prompt and targeted treatment.
RESUMO
In recent times, discovery efforts for novel antibiotics have mostly targeted carbapenemase-producing Gram-negative organisms. Two different combination approaches are pertinent: ß-lactam-ß-lactamase inhibitor (BL/BLI) or ß-lactam-ß-lactam enhancer (BL/BLE). Cefepime combined with a BLI, taniborbactam, or with a BLE, zidebactam, has been shown to be promising. In this study, we determined the in vitro activity of both these agents along with comparators against multicentric carbapenemase-producing Enterobacterales (CPE). Nonduplicate CPE isolates of Escherichia coli (n = 270) and Klebsiella pneumoniae (n = 300), collected from nine different tertiary-care hospitals across India during 2019 to 2021, were included in the study. Carbapenemases in these isolates were detected by PCR. E. coli isolates were also screened for the presence of the 4-amino-acid insert in penicillin binding protein 3 (PBP3). MICs were determined by reference broth microdilution. Higher MICs of cefepime/taniborbactam (>8 mg/L) were linked to NDM, both in K. pneumoniae and in E. coli. In particular, such higher MICs were observed in 88 to 90% of E. coli isolates producing NDM and OXA-48-like or NDM alone. On the other hand, OXA-48-like-producing E. coli or K. pneumoniae isolates were nearly 100% susceptible to cefepime/taniborbactam. Regardless of the carbapenemase types and the pathogens, cefepime/zidebactam showed potent activity (>99% inhibited at ≤8 mg/L). It seems that the 4-amino-acid insert in PBP3 (present universally in the study E. coli isolates) along with NDM adversely impact the activity of cefepime/taniborbactam. Thus, the limitations of the BL/BLI approach in tackling the complex interplay of enzymatic and nonenzymatic resistance mechanisms were better revealed in whole-cell studies where the activity observed was a net effect of ß-lactamase inhibition, cellular uptake, and target affinity of the combination. IMPORTANCE The study revealed the differential ability of cefepime/taniborbactam and cefepime/zidebactam in tackling carbapenemase-producing Indian clinical isolates that also harbored additional mechanisms of resistance. NDM-expressing E. coli with 4-amino-acid insert in PBP3 are predominately resistant to cefepime/taniborbactam, while the ß-lactam enhancer mechanism-based cefepime/zidebactam showed consistent activity against single- or dual-carbapenemase-producing isolates including E. coli with PBP3 inserts.