Investigation of in vitro susceptibility and resistance mechanisms to amikacin among diverse carbapenemase-producing Enterobacteriaceae

Objective: This study aims to assess the in vitro drug susceptibility of various Carbapenemase-Producing Enterobacteriaceae (CPE) genotypes and elucidate the underlying mechanisms of amikacin resistance.

Methods: A total of 72 unique CPE strains were collected from the Second Hospital of Jiaxing between 2019 and 2022, including 51 strains of Klebsiella pneumoniae, 11 strains of Escherichia coli, 6 strains of Enterobacter cloacae, 2 strains of Klebsiella aerogenes, 1 strain of Citrobacter freundii, and 1strain of Citrobacter werkmanii. Among these strains, 24 carried bla_KPC gene, 20 carried bla_NDM gene, 23 carried bla_OXA-48-like gene, and 5 carried both bla_KPC and bla_NDM. We measured the in vitro activity of amikacin and other common antibiotics. Strains carrying bla_OXA-48-like gene were selected for whole genome sequencing (WGS) via next-generation sequencing to identify genes related to antimicrobial resistance (AMR) and virulence factor (VF).

Results: Out of the 72 CPE strains tested, 41.7% exhibited resistance to amikacin. The drug resistance rates for K. pneumoniae, E. coli, and Enterobacter spp. were 51.0%, 27.3%, and 10.0%, respectively. The majority of the CPE strains (> 90%) displayed resistance to cephalosporins and carbapenems, while most of them were sensitive to polymyxin B and tigecycline (97.2% and 94.4%). The amikacin resistance rate was 100% for strains carrying bla_OXA-48, 20.8% for those with bla_KPC, 5.0% for those with bla_NDM, and 20.0% for those with both bla_KPC and bla_NDM. These differences were statistically significant (P < 0.05). Through sequencing, we detected aminoglycoside resistance genes rmtF and aac(6')-Ib, VF genes iucABCD and rmpA2 in OXA-48-producing multidrug resistance and highly virulent strains. These genes were located on a IncFIB- and IncHI1B-type plasmid, respectively. Both plasmids were highly homologous to the plasmid from OXA-232 strains in Zhejiang province and Shanghai province. Integration of these resistance genes into the IncFIB plasmid, facilitated by the IS6 and/or Tn3 transposons, resulted in OXA232-producing K. pneumoniae with amikacin resistance.

Conclusion: This study identified significant amikacin resistance in CPE strains, particularly in those carrying the bla_OXA-48 gene. Resistance genes rmtF and aac(6')-Ib were identified on plasmids. These results highlight the need for careful monitoring of amikacin resistance.