Purpose: This study aimed to evaluate the molecular characteristics and prevalence of clinical carbapenem-resistant Klebsiella aerogenes  (CRKA), collected during an outbreak in a Chinese tertiary hospital.
Methods: Antimicrobial susceptibility test, using 17 antibiotics, was performed on 14 CRKA isolates. The strains were examined for the presence of β-lactamase genes by PCR, and efflux pump phenotype was determined by efflux pump inhibition test. Presence of outer-membrane porins was examined. Clonal relatedness among the isolates was investigated by pulsed-field gel electrophoresis (PFGE). S1 nuclease-PFGE and plasmid incompatibility group analysis were performed to determine plasmids, and the genetic environment of bla _KPC-2 was analyzed. Epidemiological data were collected via chart review.
Results: The 14 CRKA isolates were all resistant to carbapenems; five distinct groups (PFGE types A–E) were observed. All 14 isolates carried the bla _KPC-2 gene. S1 nuclease-PFGE indicated the size of bla _KPC-2-carrying plasmids to range from 20 kb to 200 kb, and the 14 plasmids belonged to various incompatibility groups. The most frequent genetic environment of bla _KPC-2 was Tn1721- bla _KPC-2-ΔTn3-IS26. PFGE type A group, including 11 KPC-2-producing clinical isolates, was primarily responsible for dissemination.
Conclusion: Our findings suggest both transposons and vertical transmission to contribute to the transformation of bla _KPC-2. The results strongly suggest strict implementation of infection control of CRKA, in healthcare facilities.
Keywords: carbapenem resistance, Klebsiella aerogenes , Klebsiella pneumoniae  carbapenemase, plasmid, genetic environment, outbreak