Background: Ventilator-associated pneumonia (VAP) is a common nosocomial infection associated with high morbidity due to multidrug-resistant (MDR) pathogens. The purpose of this study was to determine the occurrence of extended-spectrum β-lactamase (ESBL) genes, especially bla _CTX-M-15, in Klebsiella pneumoniae  (K. pneumoniae )-associated VAP and to investigate the antimicrobial resistance patterns and molecular epidemiological characteristics of K. pneumoniae  strains.
Materials and methods: From January 2013 to December 2015, we retrospectively collected 89 VAP-causing K. pneumoniae  isolates from tertiary-care hospitals in China, among which ESBL-producing strains were assessed for antimicrobial susceptibility. Several antibiotic resistance genes of clinical relevance in K. pneumonia  isolates producing ESBL were investigated. Polymerase chain reaction (PCR) and DNA sequencing were employed to characterize the genetic contexts of bla _CTX-M-15. Conjugative plasmids carrying bla _CTX-M-15 were obtained by mating and further subjected to replicon typing. The genetic relatedness of isolates was assessed by pulsed-field gel electrophoresis (PFGE) and multilocus sequence typing.
Results: All of the 30 ESBL-producing isolates identified displayed MDR phenotype, with bla _SHV, bla _CTX-M, bla _OXA, and bla _TEM detected in 21, 21, 1, and 20 isolates, respectively. bla _CTX-M-15 was the most prevalent ESBL gene (19/30, 63.33%), and ISEcp1  was detected 48 bp upstream of 15 bla _CTX-M-15 genes. Based on S1-PFGE analyses, 25 isolates exhibited different plasmid profiles, ranging from ~70 to 320 kb. The bla _CTX-M-15 with bla _TEM and qnr  genes and the ISEcp1  element from eight isolates were co-transferrable to recipients via conjugation, with IncFIB, IncFIC, and IncFII being the most prevalent replicons. Twenty different PFGE patterns and 11 sequence types were identified, with ST304 being dominant.
Conclusion: This work reports the emergence of bla _CTX-M-15 in K. pneumoniae -induced VAP in China. We showed that IncFIB, IncFIC, and/or IncFII plasmids carrying bla _CTX-M-15 with bla _TEM, qnr  resistance genes, and the ISEcp1  element mediate the local prevalence in K. pneumoniae -associated VAP.
Keywords: Enterobacteriaceae , CTX-M-15, antibiotic resistance, horizontal gene transfer, conjugation