Complete nucleotide sequence of pHN7A8, an F33:A-:B- type epidemic plasmid carrying blaCTX-M-65, fosA3 and rmtB from China

Liangying He, Sally R Partridge, Xiaoyun Yang, Jianxia Hou, Yuting Deng, Qiongfen Yao, Zhenling Zeng, Zhangliu Chen, Jian-Hua Liu
Journal of Antimicrobial Chemotherapy 2013, 68 (1): 46-50

OBJECTIVES: To characterize a representative self-transmissible multidrug resistance plasmid pHN7A8 isolated from an Escherichia coli from a dog in China, classified as F33:A-:B- by replicon sequence typing and carrying the bla(TEM-1b), bla(CTX-M-65), fosA3 and rmtB genes conferring resistance to penicillins, cephalosporins, fosfomycin and aminoglycosides, respectively.

METHODS: pHN7A8 was sequenced using a whole-genome shotgun approach and the sequence analysed by comparison with reference plasmids.

RESULTS: pHN7A8 is a circular molecule of 76 878 bp. bla(CTX-M-65), fosA3 and rmtB are found in known contexts, interspersed with different mobile elements including ISEcp1, IS1, Tn2, IS1294, IS903 and four copies of IS26. This multiresistance region has only a single nucleotide difference from that of pXZ, an F2:A-:B- plasmid isolated from poultry in China. The pHN7A8 backbone carries genes encoding addiction and partitioning systems that promote plasmid maintenance and has a similar organization to pXZ, as well as IncFII plasmids such as R100, pC15-1a/pEK516 and pHK23, isolated in Japan, Canada/the UK and China, respectively, but with varying levels of identity, suggesting recombination.

CONCLUSIONS: pHN7A8 is a chimera that may have resulted from the acquisition, by recombination in the plasmid backbone, of the multiresistance region found in pXZ. This region appears to have evolved from the resistance determinant R100 through the stepwise integration of multiple antimicrobial resistance determinants from different sources by the actions of mobile elements and recombination. The successful dissemination of this multidrug resistance plasmid presents further challenges for the prevention and treatment of Enterobacteriaceae infections.

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