Preferential association of the heat-stable enterotoxin gene (stn) with environmental strains of Vibrio cholerae belonging to the O14 serogroup

Abstract

Toxigenic Vibrio cholerae O1 and O139 serogroups have the capacity of causing epidemic and pandemic cholera but are infrequently found in the environment. The other serogroups are abundant in aquatic environments but do not possess the virulence genes necessary for causing the disease. Of the 559 environmental strains of V. cholerae, collected during different periods from environmental samples in Calcutta, 9 (1.6%) harboured the heat-stable enterotoxin gene (stn). Six of the 9 strains belonged to the O14 serogroup. Thus, V. cholerae strains carrying the stn gene revealed preferential association with the O14 serogroup. Three of the six strains harboured the tcpA gene of the E1 Tor type, which is an unusual feature among environmental V. cholerae strains. A strain that possessed the E1 Tor type tcpA also had the CTX prophage. Pulsed field gel electrophoresis (PFGE) revealed that the stn gene positive O14 strains of V. cholerae were not clonal.

Distribution of Virulence Genes in Clinical and Environmental Vibrio cholerae Strains in Bangladesh

“…Only one (NIH831) showed the same genotype, hlyA hap ctxA zot toxR tcpI tcpA rtxA vasA vasK vasH, observed in V. cholerae O1 and O139 isolates. Seventeen non-O1/ non-O139 isolates whose genomes encoded heat-stable enterotoxin (NAG-ST) demonstrated five virulence profiles, hlyA toxR hap stn/sto rtxA vasA vaH vasK being the most common (12 out of 17) (Table 3), a finding consistent with the report that NAG-ST is mostly associated with V. cholerae non-O1/non-O139 and Vibrio mimicus strains (13,27,28), although a V. cholerae O1 isolate with genes encoding NAG-ST has also been reported (29,30).…”

Novel Cholix Toxin Variants, ADP-Ribosylating Toxins in Vibrio cholerae Non-O1/Non-O139 Strains, and Their Pathogenicity

“…The non-O1/non-O139 V. cholerae generally does not carry ctx and tcpA genes, but some strains of this group can be potentially virulent in humans, causing sporadic cases of diarrhea and extraintestinal infections (2)(3)(4). The toxigenic potential of some of these strains is attributed to the type III secretion system (T3SS), type VI secretion system (T6SS), heat-stable enterotoxin (NAG-ST), hemagglutinin protease (HAP), and zonula occludens toxin (ZOT) (5)(6)(7)(8)(9)(10). However, many non-O1/non-O139 strains isolated from patients do not contain any of these potential virulence factors.…”

Cholix Toxin, a Novel ADP-ribosylating Factor from Vibrio cholerae

“…In the environment, most strains of other serogroups (non-O1, non-O139), do not carry the genes encoding cholera toxin, and exhibit considerable genetic diversity. These strains are known to be capable of carrying many additional virulence factors, including hemolysin (12), repeats in the structural toxin (13), heat-stable enterotoxin (14), hemagglutinin/protease (15), a type III secretion system (16), and a novel type VI secretion system associated with virulence (17), and have caused sporadic outbreaks of gastrointestinal disease distinct from cholera (18,19) as well as extra-intestinal infections (20). However, unsuccessful attempts to correlate * The costs of publication of this article were defrayed in part by the payment of page charges.…”