Vibrio cholerae Non-O1, Non-O139 Serogroups and Cholera-like Diarrhea, Kolkata, India

We identified 281 Vibrio cholerae non-O1, non-O139 strains from patients with diarrhea in Kolkata, India. Cholera-like diarrhea was the major symptom (66.0%); some patients (20.3%) had severe dehydration. These strains lacked the ctxA gene but many had hlyA, rtxA, and rtxC genes. Pulsed-field gel electrophoresis showed no genetic link among strains.

V ibrio cholerae O1 has been responsible for several cholera outbreaks in developing countries. During 1992, a novel serogroup, O139, caused cholera outbreaks in India and other countries in Asia (1). These events have shown that serogroups other than O1 have major epidemiologic roles in cholera. V. cholerae O1 and O139 serogroups produce cholera toxin (CT), a critical virulence factor and express toxin coregulated pilus (TCP), which are responsible for secretory diarrhea and intestinal colonization, respectively. Serogroups other than O1 and O139 are designated as V. cholerae non-O1, non-O139, or nonagglutinating vibrios (NAGs); such serogroups have >200 somatic (O) antigens (2) and mostly lack CT-and TCP-coding genes.
Toxigenic and nontoxigenic NAGs have caused several diarrhea outbreaks in India and other countries, including Haiti (3)(4)(5)(6). In non-CT-producing NAGs, other virulence factors such as heat-stable enterotoxin (Stn), hemolysin (HlyA), repeat in toxin (RTX), and type 3 secretion systems (TTSS) have major roles in causing infections (7). In this study, we analyzed clinical characteristics of hospitalized patients with diarrhea infected with NAGs and screened strains for antimicrobial drug susceptibility, virulence genes, and genetic relatedness.

The Study
During 2002-2010, a total of 12,719 fecal specimens were collected, which represented every fifth hospitalized diarrhea patient at the Infectious Diseases Hospital in Kolkata and all children at the outpatient unit at B.C. Roy Memorial Hospital for Children in Kolkata. Fecal specimens were screened for V. cholerae and other enteric pathogens as described (8). NAGs were serotyped by using 206 polyclonal O antisera according to the protocol developed at the National Institute of Infectious Diseases (Tokyo, Japan) (2).
Antimicrobial drug susceptibility assays were performed by using the disk diffusion method and commercially available disks (Becton Dickinson, Sparks Glencoe, MD, USA), according to standards of the Clinical and Laboratory Standards Institute (9). Because these standards do not include interpretive criteria for V. cholerae, breakpoints for Enterobacteriaceae were adopted. Escherichia coli ATCC 25922 was used as a quality-control strain.
Simplex and multiplex PCRs were performed by using published methods specific for ctxA, tcpA, rtxA, rtxC, stn, and hlyA genes (classical/El Tor) and the TTSS-coding genes (7). Pulsed-field gel electrophoresis was performed according to the PulseNet standardized protocol for V. cholerae (www.pulsenetinternational. org/SiteCollectionDocuments/pfge/5.71_2009_ PNetStandProtVcholerae.pdf. Gel Compare II software (Applied Maths NV, Sint-Martens-Latem, Belgium) was used for comparison of electrophoresis patterns. This software uses a Dice similarity index and contains an unweighted pair group with arithmetic mean method.
Among age groups of patients, NAGs were detected mostly in patients >5 years of age (>72%) than in those <5 years of age (≈28%) ( Table 2). NAGs produce a spectrum of gastrointestinal symptoms ranging from asymptomatic infection to severe cholera-like illness or bloody diarrhea. In this study, most (70%) patients had watery diarrhea, which was similar to that for patients with cholera and those exclusively infected by NAGs (Table 2). Other clinical symptoms, such as dehydration status (22.3%) and fever (41.1%), were also high in patients with a single infection. In patients with mixed infections, bloody diarrhea (23.6%) and abdominal pain (41.5%) were the 2 major symptoms (Table 2), perhaps because >1 pathogen was involved.

Conclusions
Unlike our previous study (7), in this study, factors involved in the virulence of NAGs were not comprehensively elucidated in the study region. Unlike V. cholerae O1/O139, the pathogenicity of NAGs has been associated with >1 virulence factor (7,10). All NAGs lacked ctxA and El Tor tcpA genes. However, 6 (2.1%) strains had the tcpA gene; in 5 of them it was the only virulence gene detected. Most (94%) strains had the gene encoding El Tor type hemolysin, followed by rtxA (91.4%) and rtxC (75%) genes; only 5 (1.8%) had the stn gene. The RTX family includes a group of protein toxins produced by gram-negative bacteria, including V. cholerae with hemolytic, leukotoxic, and actin cross-linking activities, which may play a role in virulence (13). In this study, prevalence of NAGs that have genes encoding TTSS as the only virulence factor (41 cases) was higher than in Bangladesh and Argentina (14,15).
Prevalence of NAGs associated with severe traits of infection indicates the role of these pathogens in cholera. The pathogenic mechanism of NAGs is multifarious; there are several virulence factors in genetically distinct strains. On the basis of our results, current antimicrobial drug therapy in the clinical management of NAG-mediated diarrhea can be continued. Further epidemiologic studies are needed to determine the ecology, virulence factors, and public health role of NAGs. Figure. NotI restriction patterns of genomic DNA of representative Vibrio cholerae non-O1, non-O139 strains, Kolkata, India. Dendrogram was generated by using the unweighted pair group with arithmetic mean method.