The genetic environment influencing selection and persistence of sul2 in clinical isolates

Abstract number: P1509

Curiao T., Cantón R., Novais Â., Baquero F., Coque T.M.

Objectives: sul2 has been found as the most prevalent sulfonamide resistance gene in isolates from distinct origins and species. Firstly identified on plasmid RSF1010 in 1988, it has been frequently found adjacent to strAB and ISCR2 sequences on different plasmids. In this work, we determine sul2 genetic environment in human enterobacterial clinical isolates.

Methods: A collection of 129 clinical enterobacterial isolates containing sul2 from our institution (1988–2006) including extended spectrum- (ESBL, n = 96)/metalo- (MBL, n = 3) b-lactamase producers and non-producers (n = 30) was studied. Clonal relatedness was established (PFGE, phylogenetic groups) and antibiotic susceptibility by disk diffusion (CLSI). Genetic platforms were determined based on known sequences by PCR, long-PCR, RFLP and sequencing. Twenty-four sul2-positive strains were selected for conjugation assays. Plasmid analysis included determination of size (S1 nuclease), incompatibility groups, replicases and relaxases (PCR, hybridisation and sequencing) and rep and mob genes of recent published low %CG sul2-plasmids from environmental origin.

Results: sul2 was similarly distributed among E. coli (n = 124) phylogroups (A+B1=49%, B2+D=43%) and it was identified in strains with a variety of ESBLs (CTX-M-1, -3, -32, -15, -9, -14, SHV-5, -12, TEM-4, -24, -27, -52) and MBL (VIM-1) and, similarly, in non-producers. sul2 gene was transferable in 19/24 of cases, associated with sulfonamide, streptomycin and/or tetracycline markers. Some (n = 12) transconjugants presented more than one plasmid. No apparent association between sul2 gene and specific plasmids was observed. Some strains presented two different sul2-containing plasmids, conjugative (50–380 kb) and non-conjugative (5–12Kb). Most conjugative plasmids belonged to rep type Inc B/O. sul2 was found adjacent to ISCR2, entire or truncated (n = 48) and to both repC (pRSF1010) and strAB (n = 31) genes. Overall, 34% sul2-positive strains presented colicin genes. sul2 was also detected in 5 non-E. coli strains.

Conclusions: Despite scarce use of sulfonamides in humans, the sul2 gene is frequent in clinical isolates. Its presence is related to different plasmids and genetic platforms containing ISCR2 and other resistance genes affecting widely used antimicrobials. Co-selection processes might have fuelled persistence of sul2 gene containing isolates.