Complete Nucleotide Sequence of IncP-1β Plasmid pDTC28 Reveals a Non-Functional Variant of the bla(GES)-Type Gene

Plasmid pDTC28 was isolated from the sediments of Haihe River using E. coli CV601 (gfp-tagged) as recipient and indigenous bacteria from the sediment as donors. This plasmid confers reduced susceptibility to tetracycline and sulfamethoxazole. The complete sequence of plasmid pDTC28 was 61,503 bp in length with an average G+C content of 64.09%. Plasmid pDTC28 belongs to the IncP-1β group by phylogenetic analysis. The backbones of plasmid pDTC28 and other IncP-1β plasmids are very classical and conserved, whereas the accessory regions of these plasmids are diverse. A bla(GES-5)-like gene was found on the accessory region, and this bla(GES-5)-like gene contained 18 silent mutations and 7 missense mutations compared with the bla(GES-5) gene. The mutations resulted in 7 amino acid substitutions in GES-5 carbapenemase, causing the loss of function of the bla(GES-5)-like gene on plasmid pDTC28 against carbapenems and even β-lactams. The enzyme produced by the bla(GES-5)-like gene cassette may be a new variant of GES-type enzymes. Thus, the plasmid sequenced in this study will expand our understanding of GES-type β-lactamases and provide insights into the genetic platforms used for the dissemination of GES-type genes.