Recombination Drives Evolution of Carbapenem-Resistant Klebsiella pneumoniae Sequence Type 11 KL47 to KL64 in China.

Carbapenem-resistant , especially carbapenemase-producing Klebsiella pneumoniae, is an urgent problem in health care facilities worldwide. K. pneumoniae isolates classified as sequence type 11 (ST11) are largely responsible for the spread of carbapenem-resistant K. pneumoniae (CRKP) in China. Our previous phylogenetic reconstruction suggested that CRKP ST11 capsular locus 64 (KL64) was derived from an ST11-KL47 ancestor through recombination. However, the molecular origin of KL64 remains largely unknown, and our understanding of the recombination is incomplete. Here, we screened a global sample of 22,600 K. pneumoniae genomes and searched for KL64-harboring STs, which were found to be ST1764, ST3685, ST1764-1LV, ST30, ST505, ST147, and ST11, wherein ST1764, ST3685, ST1764-1LV, and ST30 belonged to a clonal complex, CC1764. We compared the genetic structures of representative strains from ST11-KL47, ST11-KL64, CC1764-KL64, ST505-KL64, and ST147-KL64 and further performed phylogenetic analysis and single-nucleotide polymorphism analysis among 248 isolates from all these STs. The results suggested a recombination event has occurred in a homologous ~154-kb region covering KL and the lipopolysaccharide biosynthesis locus (OL) between a recipient ST11-KL47-OL101 and a donor CC1764 (except ST30), giving rise to ST11-KL64-O2v1 strains (recombination I). Furthermore, we also found an infrequent ST11-KL64-O2v1 subclone which was not produced by recombination I but was hybridized from ST11-KL47-OL101 and ST147-KL64-O2v1 strains through recombination of a homologous ~485-kb region covering KL and OL (recombination II). Our findings provide important insights into the role of recombination in the evolution of clinical strains and the diversity of capsule and lipopolysaccharide of widely distributed KPC-associated ST11 K. pneumoniae in China. Chromosomal recombination events are considered to contribute to the genetic diversification and ultimate success of many bacterial pathogens. A previous study unravelled the molecular evolution history of ST258 strains, which have been largely responsible for the spread of KPC in the United States. Here, we used comparative genomic analyses to discover two recombination events in ST11 CRKP strains, which is a predominant KPC-associated CRKP clone in China. Two new ST11-CRKP subclones with altered capsule and lipopolysaccharide, which are two primary determinants of antigenicity and antigenic diversity among K. pneumoniae, were produced through these two recombination events, respectively. Horizontal transfer of the KL and OL appears to be a crucial element driving the molecular evolution of K. pneumoniae strains. These findings not only extend our understanding of the molecular evolutionary history of ST11 but also are an important step toward the development of preventive, diagnostic, and therapeutic strategies for CRKP.