Clinical and Environmental Isolates of Vibrio cholerae Serogroup O141 Carry the CTX Phage and the Genes Encoding the Toxin-Coregulated Pili

Abstract

We report sporadic cases of a severe gastroenteritis associated with Vibrio cholerae serogroup O141. Like O1 and O139 serogroup strains of V. cholerae isolated from cholera cases, the O141 clinical isolates carry DNA sequences that hybridize to cholera toxin (CT) gene probes. The CT genes of O1 and O139 strains are carried by a filamentous bacteriophage (termed CTX phage) which is known to use toxin-coregulated pili (TCP) as its receptor. In an effort to understand the mechanism of emergence of toxigenic O141 V. cholerae, we probed a collection of O141 clinical and environmental isolates for genes involved in TCP production, toxigenicity, virulence regulation, and other phylogenetic markers. The collection included strains isolated between 1964 and 1995 from diverse geographical locations, including eight countries and five U.S. states. Information collected about the clinical and environmental sources of these isolates suggests that they had no epidemiological association. All clinical O141 isolates hybridized to probes specific for genes encoding CT (ctx), zonula occludens toxin (zot), repetitive sequence 1 (RS1), RTX toxin (rtxA), the major subunit of TCP (tcpA), and the essential regulatory gene that controls expression of both CT and TCP (toxR). In contrast, all but one of the nonclinical O141 isolates were negative for ctx, zot, RS1, and tcpA, although these strains were positive for rtxA and toxR. The one toxigenic environmental O141 isolate was also positive for tcpA. Ribotyping and CT typing showed that the O141 clinical isolates were indistinguishable or closely related, while a toxigenic water isolate from Louisiana showed a distantly related ribotype. Nonclinical O141 isolates displayed a variety of unrelated ribotypes. These data support a model for emergence of toxigenic O141 that involves acquisition of the CTX phage sometime after these strains had acquired the pathogenicity island encoding TCP. The clonal nature of toxigenic O141 strains isolated from diverse geographical locations suggests that the emergence is a rare event but that once it occurs, toxigenic O141 strains are capable of regional and perhaps even global dissemination. This study stresses the importance of monitoring V. cholerae non-O1, non-O139 serogroup strains for their virulence gene content as a means of assessing their epidemic potential.The two most important virulence factors of Vibrio cholerae are cholera toxin (CT), a potent enterotoxin, and the toxincoregulated pilus antigen (TCP), an essential intestinal colonization factor (16). These virulence factors are encoded by accessory genetic elements which are nearly always present in clinical isolates of V. cholerae but are frequently absent in strains isolated from environmental sources, such as water or shellfish (6,16,17). The ctxAB genes are located on the CTX genetic element, which is composed of a 4.5-kb central core region flanked by one or more copies of a repetitive sequence (RS1 or RS2) (34). The core and RS2, a portion of the CTX element, are now known to corresp...

Distribution of virulence markers in clinical and environmental Vibrio cholerae non-O1/non-O139 strains isolated in Brazil from 1991 to 2000

“…However, our results contradict the assumption that most cholera toxin-producing strains are also positive for TCP, since TCP is known to be the receptor for CTXφ infection of V. cholerae. In fact, our results appear to be consistent with data from recent studies that report the presence of the two virulence genes found in epidemic strains, ctxAB and tcpA, in environmental and clinical strain of serogroups other than O1 and O139 5,10,27,28,31,32 .…”

Identification of a domain within the multifunctional Vibrio cholerae RTX toxin that covalently cross-links actin

“…Additional analyses demonstrate that the gene encoding VcRtxA is absent in O1 classical biotype strains of V. cholerae because of a 7-kb deletion within the rtx operon (4), but is present in El Tor, O139, and non-O1 clinical and environmental isolates (9)(10)(11). The ubiquitous presence of VcRtxA suggests that this toxin is an important virulence factor of V. cholerae.…”

Genomic characterization of non-O1, non-O139 Vibrio cholerae reveals genes for a type III secretion system

“…Most nonpathogenic, environmental isolates express other O antigens and are referred to as ''non-O1, non-O139.'' However, some non-O1, non-O139 V. cholerae are clearly pathogenic and have caused outbreaks or sporadic cases of gastroenteritis and extraintestinal infections in humans (8)(9)(10)(11)(12).…”