Mobilization of Tn1721-like structure harboring bla(CTX-M-27) between P1-like bacteriophage in Salmonella and plasmids in Escherichia coli in China

The aim of this study was to explore the characteristics of bla(CTX-M-27 )carriage and mobilization in Salmonella and Escherichia coli isolates from food-producing animals in China. A total of 2280 E. coli and 229 Salmonella isolates collected from food animals from June 2003 to September 2014 were screened for the presence of bla(CTX-M-27) gene. The bla(CTX-M-27)-positive isolates were typed and plasmid DNA sequenced to determine the genetic context of bla(CTX-M-27) and plasmid types present. Bacterial fitness was evaluated by growth curve and plasmid stability in vitro. CTX-M-27-positive E. coli (18, 0.79 %) and Salmonella (34, 14.85 %) were detected. PFGE profiles of CTX-M-27-positive strains revealed a wide variety of genotypes and S. Indiana was the most prevalent semtype. Replicon typing, S1-PFGE and hybridization of CTX-M-27-carrying plasmids confirmed that bla(CTX-M-27) gene was located on IncFII (12/18), IncN (4/18), and non-typeable (2/18) plasmids in E. coli and on P1-like bacteriophage (21/34), IncP (4/34), IncFIB (4/34), IncN (2/34), IncHI2 (2/34), and IncA/C (1/34) plasmids in Salmonella. Comparison and analysis of gene context of bla(CTX-M-27) in P1-like bacteriophage and plasmids revealed they shared the same structure and contained an identical genetic context with the Tn1721-like structure Delta ISE(cp)1B-bla(CTX-M-27)-IS903D-iroN-Delta map-Tn1721. In addition, plasmid stability tests indicated that the bla(CTX-M-27) P1-like bacteriophage were more stable than plasmids in the absence of cefotaxime selective pressure. These results demonstrate that Tn1721-like transposons harboring CTX-M-27 could be mobilized between different plasmids in E. coli and P1-like bacteriophage disseminated among Salmonella.

Automated summary

The study revealed the presence of bla(CTX-M-27) gene in isolates of E. coli and Salmonella from food-producing animals in China. The genetic context and plasmid types of bla(CTX-M-27) were determined, showing a variety of plasmids carrying the gene in both bacteria. Additionally, stability tests indicated CTX-M-27 P1-like bacteriophage was more stable than plasmids in the absence of cefotaxime selective pressure.