Chromosomal location of the fosA3 and blaCTX-M genes in Proteus mirabilis and clonal spread of Escherichia coli ST117 carrying fosA3-positive IncHI2/ST3 or F2:A-:B- plasmids in a chicken farm

Abstract The aim of this study was to investigate the spread and location of the fosA3 gene among Enterobacteriaceae from diseased broiler chickens. Twenty-nine Escherichia coli and seven Proteus mirabilis isolates recovered from one chicken farm were screened for the presence of plasmid-mediated fosfomycin resistance genes by PCR. The clonal relatedness of fosA3 -positive isolates, the transferability and location of fosA3 , and the genetic context of the fosA3 gene were determined. Seven P. mirabilis isolates with three different pulsed-field gel electrophoresis (PFGE) patterns and five E. coli isolates belonging to sequence type 117 (ST117) and phylogenetic group D were positive for fosA3 and all carried the bla CTX-M gene. In E. coli , the genetic structures IS 26 –IS Ecp1–bla CTX-M-65 –IS 26 – fosA3 –1758 bp–IS 26 and IS 26 –IS Ecp1 – bla CTX-M-3 – bla TEM-1 –IS 26 – fosA3 –1758 bp–IS 26 were present on transferable IncHI2/ST3 and F2:A-:B- plasmids, respectively. However, fosA3 was located on the chromosome of the seven P. mirabilis isolates. IS 26 –IS Ecp1 - bla CTX-M-65 –IS 26 – fosA3 –1758 bp–IS 26 and IS 26 – bla CTX-M-14 –611 bp– fosA3 –1222 bp–IS 26 were detected in three and four P. mirabilis isolates, respectively. Minicircles that contained both fosA3 and bla CTX-M-65 were shared between E. coli and P. mirabilis . This is the first report of the fosA3 gene integrated into the chromosome of P. mirabilis isolates with the bla CTX-M gene. The emergence and clonal spread of avian pathogenic E. coli ST117 with the feature of multidrug resistance and high virulence are a serious problem.