北京大学第二临床医学院知识库

Background The extended spectrum p-lactamase (ESBL)-producing Escherichia coli (E. coli) and Klebsiella pneumoniae (K. pneumoniae) are the major pathogens causing pneumonia and have a significant impact on the clinical course. Limited data exist on molecular characterization of ESBL-producing E. coli and K. pneumoniae that cause pneumonia. The aim of this study was to investigate the comprehensive multilevel characteristics of E. coli and K. pneumoniae causing pneumonia in China for the first time.

Methods E. coli (17) and K. pneumoniae (21) isolates responsible for pneumonia were isolated from 1270 specimens collected in a prospective multi-center study in eight teaching hospitals in China from June to December in 2007. The susceptibilities, ESBL confirmation, sequence typing, bla(CTX-M) and bla(SHV) genes, their genetic environment and plasmid Inc/rep types were determined.

Results Sixteen E. coli (94.1%) and eleven K. pneumoniae (52.4%) isolates were ESBL producers. About 77.8% and 66.7% of them were resistance to ciprofloxacin and levofloxacin, and 100% were susceptible to imipenem. The most prevalent ESBL gene was CTX-M-14, followed by SHV-2, CTX-M-15, CTX-M-3, CTX-M-65, SHV-12, SHV-26 and SHV-28. SHV-1 and SHV-11 were also detected and coexisted with bla(CTX-Ms) in five strains, and three strains contained only SHV-1. All CTX-M-14 were detected ISEcp1 upstream and nine were found IS903 downstream and the majority of them (64.3%) were carried by IncF plasmids. All bla(SHV) were flanked by recF and deoR, located on IncF, IncN, IncX and IncH plasmids. Two SHV-2, one SHV-1 and the only SHV-28 were further preceded by IS26. Genes lacY and lacZ were detected at further upstream of two bla(SHV-1). The K. pneumoniae carrying SHV-28 was susceptible to beta-lactams, and no mutations or deletions in gene or promoter sequences were identified to account for susceptibility. Multilocus sequence typing experiments showed the ESBL-producing strains were genetically diverse.

Conclusions The rate of occurrence of bla(ESBL) in E. coli and K. pneumoniae causing pneumonia was high, and bla(CTX-M-14) was dominant and probably mobilized by ISEcp1 mainly on IncF plasmids. Importantly, unexpressed bla(ESBL) genes may occur in susceptible isolates and hence may have clinical implications. Chin Med J 2012;125(5):894-900