Emergence of bla CTX-M-55 associated with fosA, rmtB and mcr gene variants in Escherichia coli from various animal species in France

Abstract

In Asian countries, bla CTX-M-55 is the second most common ESBL-encoding gene. bla CTX-M-55 frequently co-localizes with fosA and rmtB genes on epidemic plasmids, which remain sporadic outside Asia. During 2010-13, we investigated CTX-M-55 -producing Escherichia coli isolates and their co-resistance to fosfomycin, aminoglycosides, fluoroquinolones and colistin as part of a global survey of ESBLs in animals in France. Methods: bla CTX-M-55 , fosA, rmtB and plasmidic quinolone and colistin resistance genes were characterized by PCR, sequencing and hybridization experiments. Plasmids were classified according to their incompatibility groups and subtypes. Genotyping was performed by MLST and repetitive extragenic palindromic sequence-based PCR. Results: Twenty-one E. coli isolates from bovines (n=16), dogs (n=2), horses (n=2) and a monkey harboured bla CTX-M-55 , were MDR and belonged to ST744 (n=9) and 10 other clones. bla CTX-M-55 was mostly located on IncF (n=19), but also on IncI1 (n=2) plasmids. On IncF33:A1:B1 plasmids, bla CTX-M-55 co-localized with the rmtB and aac(60)-Ib genes and in one isolate with the fosA3 allele. Ten IncF46:A-:B20 plasmids, which were found in different clones from unrelated animals, also carried the mcr-3 gene. bla CTX-M-55 -carrying IncF18:A-:B1 plasmids were found in different animal species from distinct locations and periods, and one additionally carried the fosA4 gene. One isolate harboured the mcr-1 gene, which did not co-localize with bla CTX-M-55 . Conclusions: A large diversity of E. coli clones and plasmid types supported the spread of bla CTX-M-55 , together with atypical resistance genes, in various animal species in France. fosA and rmtB genes are emerging among animals in Europe and this issue is of concern for public health.