Complete sequencing of the FII plasmid pHK01, encoding CTX-M-14, and molecular analysis of its variants among Escherichia coli from Hong Kong

Objectives: We characterized plasmids encoding CTX-M-14 beta-lactamase originating from Escherichia coli isolates recovered from patients with uncomplicated cystitis or individuals with faecal colonization in Hong Kong from 2002 to 2004. Methods: Plasmids carrying CTX-M-14 were studied by conjugation, replicon typing, S1 nuclease-PFGE and plasmid PCR-restriction fragment length polymorphism (RFLP). The complete sequence of pHK01, a 70 kb plasmid encoding CTX-M-14 from an E. coli strain, was determined and the results compared with reference plasmids and aligned with GenBank data. Results: The bla(CTX-M-14) plasmids could be transferred in 23 of 44 E. coli strains tested. Among the 23 transconjugants, the replicon types of the CTX-M-14-encoding plasmid were FII (n = 13), I1-I gamma (n = 4), F1B (n = 2), FII and I1-I gamma (n = 1), K (80 kb, n = 1) and undetermined (n = 2). Plasmid pHK01 (FII replicon) shares a high degree of homology with R100 except mainly for a 11 kb variable region containing bla(CTX-M-14) (with an upstream ISEcp1 and a downstream truncated IS903), an iron transport system, an outer membrane protein (malB, maltoporin) and a putative toxin-antitoxin plasmid stability system (yacABC). It was highly related to bla(CTX-M-14) (pKF3-70) and bla(CTX-M-24) (pEG356) plasmids reported from mainland China in 2006 and Vietnam in 2007, respectively. Subtyping by a plasmid PCR-RFLP scheme showed that 10 of the 13 FII plasmids originating from isolates collected by multiple laboratories exhibited either identical or highly similar profiles. Conclusions: This study showed that narrow host-range FII plasmids play important roles in the dissemination of CTX-M-14. FII plasmids closely related to pHK01 have disseminated widely in the Hong Kong community.