ISEcp1-mediated transposition of blaKPC into the chromosome of a clinical isolate of Acinetobacter baumannii from Puerto Rico

Carbapenems are the last-resort antibiotics for the treatment of infections caused by multidrug-resistant Gram-negative bacilli. Klebsiella pneumoniae carbapenemase (KPC) hydrolyses beta-lactam antibiotics including the carbapenems. KPCs have been detected in Enterobacteriaceae and Pseudomonas aeruginosa isolates worldwide associated with transposon Tn4401 commonly located in plasmids. Acinetobacter baumannii has become an important multidrug-resistant nosocomial pathogen capable of hydrolysing the carbapenem antibiotics. KPC-producing A. baumannii has so far only been reported in Puerto Rico. During a surveillance study, four KPC-producing A. baumannii with identical pulse type were identified in a single institution. The objectives of this study were to characterize the KPC genetic background and the allelic diversity of one of the isolates. Next-generation sequencing and multilocus sequence typing (MLST) were performed. Molecular characterization of the isolate demonstrated bla(KPC) in Tn4401b located in the bacterial chromosome within a 26.5 kb DNA fragment, which included a KO-like element (18.9 kb) very similar to that described previously in a K pneumoniae plasmid and a 7.6 kb DNA fragment with 98% homology to a putative plasmid from Yersinia pestis strain PY-95. Our data suggested that the 26.5 kb DNA fragment harbouring bla(KPC) was integrated in the chromosome by a transposition event mediated by the transposase of ISEcp1 found in the Ka-like element. MLST showed a novel sequence type, ST250. To our knowledge, this is the first report of the identification of the genetic background of bla(KPC) in A. baumannii.