Putative virulence traits and pathogenicity of Vibrio cholerae Non-O1, Non-O139 isolates from surface waters in Kolkata, India

Abstract

Vibrio cholerae non-O1, non-O139 was isolated from natural surface waters from different sites sampled in diarrhea endemic zones in Kolkata, India. Twenty-one of these isolates were randomly selected and included in the characterization. The multiserogroup isolates were compared by their virulence traits with a group of clinical non-O1, non-O139 isolates from the same geographic area. Of the 21 environmental isolates, 6 and 14 strains belonged to Heiberg groups I and II, respectively. Three of the environmental isolates showed resistance to 2,2-diamine-6,7-diisopropylpteridine phosphate. All of the non-O1, non-O139 strains were positive for toxR, and except for one environmental isolate, none of them were positive for tcpA in the PCR assay. None of the isolates were positive for genes encoding cholera toxin (ctxA), heat-stable toxin (est), heat-labile toxin (elt), and Shiga toxin variants (stx) of Escherichia coli. Additionally, except for one environmental isolate (PC32), all were positive for the gene encoding El Tor hemolysin (hly). The culture supernatants of 86% (18 of 21) of the environmental isolates showed a distinct cytotoxic effect on HeLa cells, and some of these strains also produced cell-rounding factor. The lipase, protease, and cell-associated hemagglutination activities and serum resistance properties of the environmental and clinical isolates did not differ much. However, seven environmental isolates exhibited very high hemolytic activities (80 to 100%), while none of the clinical strains belonged to this group. The environmental isolates manifested three adherence patterns, namely, carpet-like, diffuse, and aggregative adherence, and the clinical isolates showed diffuse adherence on HeLa cells. Of the 11 environmental isolates tested for enteropathogenic potential, 8 (73%) induced positive fluid accumulation (>/=100) in a mouse model, and the reactivities of these isolates were comparable to those of clinical strains of non-O1, non-O139 and toxigenic O139 V. cholerae. Comparison of the counts of the colonized environmental and clinical strains in the mouse intestine showed that the organisms of both groups had similar colonizing efficiencies. These findings indicate the presence of potentially pathogenic V. cholerae non-O1, non-O139 strains in surface waters of the studied sites in Kolkata.

FIG. 1.

Sample collection sites. 1, Rajarhat; 2, Dum Dum; 3, Kalighat; 4, Chetla; 5, Mudialy; 6, Taratala; 7, Behala; 8, Jadavpur; 9, Sonarpur; 10, Taldi; 11, Canning; 12, South Barasat; 13, Laksmikantapur; 14, Bally; 15, Deulti; and 16, Budge Budge.

FIG. 2.

Amplification of toxR (900 bp) (A), ompW_Vc (588 bp) (B), and hlyA (El Tor; 481 bp) (C) by PCR. (A and B) Lanes: 1, V. cholerae O139 strain SG24 (positive control); 2, non-O1, non-O139 strain PC1; and 3, Aeromonas hydrophila strain PC16 (negative control). (C) Lanes 1 and 3, V. cholerae strains NB2 (O1; El Tor; positive control) and PC1; lane 2, A. hydrophila strain PC16 (negative control); lane M, 100-bp ladder.

FIG. 3.

Effects of culture filtrates of the environmental isolates on HeLa cells. Confluent growth of HeLa cells (A), cytotoxic effect (B), and cytotoxic effect associated with cell rounding (C). Magnification, ×400.

FIG. 4.

Adherence patterns of the environmental isolates on HeLa cells by Giemsa stain. (A) Carpet-like adherence to HeLa cells and a glass surface. (B) Diffuse adherence; bacteria are dispersed over the cell surface and the cell matrix. (C) Aggregative adherence; bacteria adhere to each other away from the cells, as well as to the cell surface. Magnification, ×400.