Virulence factors and genetic diversity of clinical and environmental Vibrio cholerae non-O1, non-O139 strains isolated in Argentina.

SAKA HA; VIÑAS MR; BINSZTEIN N; CARRANZA P; SOLA C; BOCCO JL; PICHEL M.

Cordoba

Congreso; Congreso Argentino de Microbiologia; 2007

Asociacion Argentina de Microbiologia

V. cholerae is the causative agent of cholera, a severe diarrhea transmitted through contaminated food or drinking-water or by the faecal-oral route mainly in developing countries. Cholera toxin (CT), a potent enterotoxin encoded in the CTXphi bacteriophage and toxin co-regulated pilus (TCP), a colonization factor, are critical in the pathogenesis of cholera. V. cholerae includes more than 200 serogroups from which only CT+ TCP+ strains from O1 and O139 serogroups are associated to cholera epidemics. The remaining serogroups, referred to as V. cholerae non-O1, non-O139 (VCN), mostly lack CT and TCP. However, VCN may cause sporadic outbreaks of watery diarrhea, inflammatory enterocolitis, sepsis and soft tissue infections. There is evidence indicating that environmental VCN may acquire virulence genes and eventually become epidemic. Thus, the study VCN virulence may help to understand the epidemiology and the origin of pathogenic V. cholerae strains. In this work, 63 VCN (clinical, 22; environmental, 38 and food, 3) isolated in 8 provinces (1992-2003), were used to investigate the prevalence of 9 different virulence genes by PCR. A subset of 30 strains was selected to study their enterotoxic potential in rabbit ileal loops (RIL) and their genetic diversity by PFGE. Results obtained by PCR showed that hlyA (encoding V. cholerae cytolysin), toxR (encoding a virulence-related transcriptional regulator) and rtxA (encoding RTX toxin) were the most prevalent virulence genes as they were detected in 100%, 96.9% and 96.9% of the isolates, respectively. Only one strain, isolated from environmental water, harbored ctxA (encoding the catalytic subunit of CT). No zot (encoding zonula occludens toxin) or ace (encoding accessory cholera enterotoxin) positive strains were detected. Though none of the isolates were positive for tcpA (encoding the A subunit of TCP), 12.7% carried tcpI (a gene related to TCP expression), pointing out to the possibility that these strains may have autochthonous TCP variants which could probably be functional as receptors for CTXphi and may consequently acquire epidemic potential. The stn gene (encoding a termostable enterotoxin) was detected in 15.9% of the isolates. The RIL assay showed that most of the strains were capable of inducing fluid accumulation (FA), with the highest FA values for the tcpI+ and for the stn+ strains. The PFGE patterns revealed the existence of a wide variety of VCN clones. Interestingly, two environmental tcpI+ isolates presented the same PFGE pattern, two clinical isolates showed an indistinguishable PFGE profile and other three clinical strains had a closely related fingerprint PFGE pattern. This is the first comprehensive study about the genetic diversity and the virulence properties of VCN in Argentina.