In vivo Acquisition of Carbapenemase Gene bla(KPC-2) in Multiple Species of Enterobacteriaceae through Horizontal Transfer of Insertion Sequence or Plasmid

Objectives: Current worldwide spread of carbapenem resistance in Enterobacteriaceae constitutes a critical public health threat. This study aims to investigate how carbapenem resistance is acquired in Enterobacteriaceae in patients during antimicrobial therapy. Methods: Clinical strains from the same anatomical site of the same patients that converted from carbapenem-susceptible to resistant during antimicrobial therapy and showed identical or similar PFGE patterns were identified. The similarly sized plasmids carried by the susceptible and resistant strains, the latter containing the carbapenemase genes, were sequenced and analyzed. Results: Paired strains were identified from four patients: three had neurosurgical conditions while the other had acute exacerbation of COPD. Two pairs of Klebsiella pneumoniae (KP1-S/R and KP2-S/R, S and R indicating susceptible and resistant strains, respectively), one pair of Morganella morganii (MM-S/R) and one pair of Enterobacter aerogenes (EA-S/R) were collected. All four carbapenem-resistant strains carried plasmids harboring bla(KPC−2). Compared with the similarly sized plasmids in KP1-S and KP2-S, an insertion sequence that includes ISKpn6-like, bla(KPC−2) and ISKpn8 was noted in pKP1-R and pKP2-R. Strains MM-R and EA-R had bla(KPC−2)-carrying plasmids not resembling plasmids in strains MM-S and EA-S suggesting their new acquisition while on therapy. Conclusions: Enterobacteriaceae can acquire carbapenem resistance during antimicrobial therapy through horizontal transfer of an insertion sequence or plasmid.