Genetic diversity and in vitro activity of ceftazidime/avibactam and aztreonam/avibactam against imipenem-resistant Enterobacteriaceae isolates in Southwest China: A single-centre study.

OBJECTIVES:The aim of this study was to investigate the molecular mechanisms of imipenem resistance in Enterobacteriaceae and to assess the antimicrobial activities of ceftazidime/avibactam (CAZ/AVI) and aztreonam/avibactam (ATM/AVI) against imipenem-resistant clinical isolates in a tertiary hospital in China. METHODS:A total of 91 imipenem-resistant Enterobacteriaceae were collected and genes encoding carbapenemases, ESBLs, AmpC β-lactamases and porins were detected using PCR. MICs and susceptibility were determined using in-house-prepared broth microdilution panels and were interpreted according to CLSI breakpoints. RESULTS:Imipenem-resistant isolates comprising 54 Klebsiella pneumoniae, 18 Escherichia coli, 8 Enterobacter cloacae, 6 Serratia marcescens, 3 Klebsiella oxytoca and 2 Klebsiella aerogenes were collected independently. Five different carbapenemase genes were identified, namely blaKPC-2 (n = 60), blaNDM-5 (n = 14), blaNDM-1 (n = 11), blaKPC-3 (n = 4) and blaIMP-4 (n = 1). Among the 91 carbapenem-resistant Enterobacteriaceae (CRE), 85 isolates harboured at least one ESBL and/or AmpC gene, including 5 strains without carbapenemase-encoding genes. Moreover, 31 K. pneumoniae carried ompK35 and/or ompK36 mutations. MLST results showed that the K. pneumoniae belonged to 12 different STs, with ST11 being predominant (29/54; 53.7%). Overall, 17.6%, 25.3%, 41.8%, 65.9% and 100% of the CRE strains were susceptible to amikacin, trimethoprim/sulfamethoxazole, tetracycline, CAZ/AVI and ATM/AVI, respectively. CONCLUSION:This study revealed that CRE isolates differ significantly in their species, STs, porins and carbapenemase genes in a single Chinese hospital. ATM/AVI exhibited potent activity against CRE isolates, even for the most notorious double-carbapenemase-producers with porin defects, whereas CAZ/AVI was active against all the non-metallo-β-lactamase-producing isolates.