ompU genes in non-toxigenic Vibrio cholerae associated with aquaculture

Genomic attributes of Vibrio cholerae O1 responsible for 2022 massive cholera outbreak in Bangladesh

In 2022, one of its worst cholera outbreaks began in Bangladesh and the icddr,b Dhaka hospital treated more than 1300 patients and ca. 42,000 diarrheal cases from March-1 to April-10, 20221. Here, we present genomic attributes of V. cholerae O1 responsible for the 2022 Dhaka outbreak and 960 7th pandemic El Tor (7PET) strains from 88 countries. Results show strains isolated during the Dhaka outbreak cluster with 7PET wave-3 global clade strains, but comprise subclade BD-1.2, for which the most recent common ancestor appears to be that responsible for recent endemic cholera in India. BD-1.2 strains are present in Bangladesh since 2016, but not establishing dominance over BD-2 lineage strains2 until 2018 and predominantly associated with endemic cholera. In conclusion, the recent shift in lineage and genetic attributes, including serotype switching of BD-1.2 from Ogawa to Inaba, may explain the increasing number of cholera cases in Bangladesh.

The Vibrios: Scavengers, Symbionts, and Pathogens from the Sea

Bacteria belonging to the genus Vibrio are major carbon cycle drivers in marine and estuarine environments. As is the case for most carbon cycle participants, the vibrios metabolize degradable compounds such as sugars and amino acids; they can also degrade some more recalcitrant compounds including hydrocarbons and lignins. Several vibrios are symbionts and even fewer are pathogenic for animals, including humans and marine animals and plants. This paper reviews Vibrio ecology, metabolism, and survival, and it also discusses select vibrios-V. alginolyticus, V. cholerae, V. coralliilyticus, V. cortegadensis, V. fischeri, V. harveyi, V. harveyi var. carahariae, V. ordalii, V. parahaemolyticus, and V. vulnificus.

Factors affecting infection of corals and larval oysters by Vibrio coralliilyticus

The bacterium Vibrio coralliilyticus can threaten vital reef ecosystems by causing disease in a variety of coral genera, and, for some strains, increases in virulence at elevated water temperatures. In addition, strains of V. coralliilyticus (formally identified as V. tubiashii) have been implicated in mass mortalities of shellfish larvae causing significant economic losses to the shellfish industry. Recently, strain BAA-450, a coral pathogen, was demonstrated to be virulent towards larval Pacific oysters (Crassostrea gigas). However, it is unclear whether other coral-associated V. coralliilyticus strains can cause shellfish mortalities and if infections are influenced by temperature. This study compared dose dependence, temperature impact, and gross pathology of four V. coralliilyticus strains (BAA-450, OCN008, OCN014 and RE98) on larval C. gigas raised at 23°C and 27°C, and evaluated whether select virulence factors are required for shellfish infections as they are for corals. All strains were infectious to larval oysters in a dose-dependent manner with OCN014 being the most pathogenic and BAA-450 being the least. At 27°C, higher larval mortalities (p < 0.05) were observed for all V. coralliilyticus strains, ranging from 38.8−93.7%. Gross pathological changes to the velum and cilia occurred in diseased larvae, but there were no distinguishable differences between oysters exposed to different V. coralliilyticus strains or temperatures. Additionally, in OCN008, the predicted transcriptional regulator ToxR and the outer membrane protein OmpU were important for coral and oyster disease, while mannose sensitive hemagglutinin type IV pili were required only for coral infection. This study demonstrated that multiple coral pathogens can infect oyster larvae in a temperature-dependent manner and identified virulence factors required for infection of both hosts.

A Comparative Analysis of Vibrio cholerae Contamination in Point-of-Drinking and Source Water in a Low-Income Urban Community, Bangladesh

Bangladesh is a cholera endemic country with a population at high risk of cholera. Toxigenic and non-toxigenic Vibrio cholerae (V. cholerae) can cause cholera and cholera-like diarrheal illness and outbreaks. Drinking water is one of the primary routes of cholera transmission in Bangladesh. The aim of this study was to conduct a comparative assessment of the presence of V. cholerae between point-of-drinking water and source water, and to investigate the variability of virulence profile using molecular methods of a densely populated low-income settlement of Dhaka, Bangladesh. Water samples were collected and tested for V. cholerae from "point-of-drinking" and "source" in 477 study households in routine visits at 6 week intervals over a period of 14 months. We studied the virulence profiles of V. cholerae positive water samples using 22 different virulence gene markers present in toxigenic O1/O139 and non-O1/O139 V. cholerae using polymerase chain reaction (PCR). A total of 1,463 water samples were collected, with 1,082 samples from point-of-drinking water in 388 households and 381 samples from 66 water sources. V. cholerae was detected in 10% of point-of-drinking water samples and in 9% of source water samples. Twenty-three percent of households and 38% of the sources were positive for V. cholerae in at least one visit. Samples collected from point-of-drinking and linked sources in a 7 day interval showed significantly higher odds (P < 0.05) of V. cholerae presence in point-of-drinking compared to source [OR = 17.24 (95% CI = 7.14-42.89)] water. Based on the 7 day interval data, 53% (17/32) of source water samples were negative for V. cholerae while linked point-of-drinking water samples were positive. There were significantly higher odds (p < 0.05) of the presence of V. cholerae O1 [OR = 9.13 (95% CI = 2.85-29.26)] and V. cholerae O139 [OR = 4.73 (95% CI = 1.19-18.79)] in source water samples than in point-of-drinking water samples. Contamination of water at the point-of-drinking is less likely to depend on the contamination at the water source. Hygiene education interventions and programs should focus and emphasize on water at the point-of-drinking, including repeated cleaning of drinking vessels, which is of paramount importance in preventing cholera.

Toxigenic Vibrio cholerae identified in estuaries of Tanzania using PCR techniques

The current study assessed the occurrence of the Vibrio cholerae serogroups O1 and O139 in environmental samples along salinity gradients in three selected estuaries of Tanzania both through culture independent methods and by cultured bacteria. Occurrence of V. cholerae was determined by PCR targeting the V. cholerae outer membrane protein gene ompW. Furthermore, the presence of toxigenic strains and serogroups O1 and O139 was determined using multiplex PCR with specific primers targeting the cholera toxin gene subunit A, ctxA, and serotype specific primers, O1-rfb and O139-rfb, respectively. Results showed that V. cholerae occurred in approximately 10% (n = 185) of both the environmental samples and isolated bacteria. Eight of the bacteria isolates (n = 43) were confirmed as serogroup O1 while one belonged to serogroup O139, the first reported identification of this epidemic strain in East African coastal waters. All samples identified as serogroup O1 or O139 and a number of non-O1/O139 strains were ctxA positive. This study provides in situ evidence of the presence of pathogenic V. cholerae O1 and O139 and a number of V. cholerae non-O1/O139 that carry the cholera toxin gene in estuaries along the coast of Tanzania.

Construction and characterization of a Vibrio cholerae serogroup O139 vaccine candidate by genetic engineering

The present study aimed to construct and evaluate the live attenuated Vibrio cholerae serogroup O139 vaccine candidate, in which genes encoding protective antigens were integrated into the chromosomal DNA. Using the initial strain, O139-ZJ9693, the toxin-linked cryptic (TLC) and cholera toxin (CTX) genetic elements and repeats in the toxin (RTX) gene cluster were deleted from its chromosomal DNA, and the cholera toxin genes, ctxB and rstR, were transferred into the chromosome to construct the candidate vaccine strain. The expression of ctxB and the vaccine virulence were then examined. Polymerase chain reaction (PCR), enzymatic digestion and electrophoresis were performed to confirm that TLC, CTX and RTX were deleted, and that ctxB and rstR were transferred into the vaccine candidate DNA. According to the preliminary evaluation, the ctxB gene exhibited cholera toxin subunit B expression, and no enterotoxigenic or cytotoxic effects were observed in this strain. In conclusion, a recombinant strain containing genes encoding protective antigens that replaced virulence-associated genes was successfully constructed in the present study; this candidate strain may have the potential to be utilized to further evaluate the immune response.

Evaluation of monoclonal antibody based immunochromatographic strip test for direct detection of Vibrio cholerae O1 contamination in seafood samples

A strip test for the detection of Vibrio cholerae O1 was developed using two monoclonal antibodies (MAbs), VC-223 and VC-1226, specific to the lipopolysaccharides of Vibrio cholerae O1 Inaba and Ogawa serovars. The sensitivity of the test was 5 × 10(5)cfu/mL which was similar to that of dot blot test. The detection limit could be improved to 1cfu/mL of the original bacterial content after pre-incubation of the bacterium in alkaline peptone water (APW) for 12h. Detection of V. cholerae O1 in various fresh seafood samples such as shrimp, blood clam, mussel and oyster could be performed directly with sensitivities ranged from 5 × 10(5) to 10(6)cfu/mL. After pre-enrichment of the shrimp sample in APW, the detection sensitivities increased to 10(2) to 10CFU/mL of the original bacterial content after incubation for 12 and 24h. However, the detection sensitivities were also depending on the content of the other bacteria that might inhibit the growth of V. cholerae during pre-enrichment step. The V. cholerae O1 strip test has advantages in speed, and simplicity in not requiring sophisticated equipment or specialized skills and the sample could be directly examined without requirement for sample processing.

Alkaline protease from a non-toxigenic mangrove isolate of Vibrio sp. V26 with potential application in animal cell culture

Vibrio sp. V26 isolated from mangrove sediment showed 98 % similarity to 16S rRNA gene of Vibrio cholerae, V. mimicus, V. albensis and uncultured clones of Vibrio. Phenotypically also it resembled both V. cholerae and V. mimicus. Serogrouping, virulence associated gene profiling, hydrophobicity, and adherence pattern clearly pointed towards the non-toxigenic nature of Vibrio sp. V26. Purification and characterization of the enzyme revealed that it was moderately thermoactive, nonhemagglutinating alkaline metalloprotease with a molecular mass of 32 kDa. The application of alkaline protease from Vibrio sp. V26 (APV26) in sub culturing cell lines (HEp-2, HeLa and RTG-2) and dissociation of animal tissue (chick embryo) for primary cell culture were investigated. The time required for dissociation of cells as well as the viable cell yield obtained by while administering APV26 and trypsin were compared. Investigations revealed that the alkaline protease of Vibrio sp. V26 has the potential to be used in animal cell culture for subculturing cell lines and dissociation of animal tissue for the development of primary cell cultures, which has not been reported earlier among metalloproteases of Vibrios.

Indigenous Vibrio cholerae strains from a non-endemic region are pathogenic

Of the 200+ serogroups of Vibrio cholerae, only O1 or O139 strains are reported to cause cholera, and mostly in endemic regions. Cholera outbreaks elsewhere are considered to be via importation of pathogenic strains. Using established animal models, we show that diverse V. cholerae strains indigenous to a non-endemic environment (Sydney, Australia), including non-O1/O139 serogroup strains, are able to both colonize the intestine and result in fluid accumulation despite lacking virulence factors believed to be important. Most strains lacked the type three secretion system considered a mediator of diarrhoea in non-O1/O13 V. cholerae. Multi-locus sequence typing (MLST) showed that the Sydney isolates did not form a single clade and were distinct from O1/O139 toxigenic strains. There was no correlation between genetic relatedness and the profile of virulence-associated factors. Current analyses of diseases mediated by V. cholerae focus on endemic regions, with only those strains that possess particular virulence factors considered pathogenic. Our data suggest that factors other than those previously well described are of potential importance in influencing disease outbreaks.

Differentiation among the Vibrio cholerae serotypes O1, O139, O141 and non-O1, non-O139, non-O141 using specific monoclonal antibodies with dot blotting

Seven different monoclonal antibodies (MAbs) specific to only Vibrio cholerae were produced using a combination of five representative serotypes of V. cholerae for immunization. The first three MAbs (VC-93, VC-82 and VC-223) were specific to the V. cholerae serogroup O1 with different avidity for the serotypes O1 Inaba and O1 Ogawa. The fourth and the fifth MAbs were specific to V. cholerae O139 (VC-812) or O141 (VC-191) serogroups, respectively. The sixth MAb (VC-26) bound to all three serogroups of V. cholerae. The seventh MAb (VC-63) bound to all twenty five isolates of V. cholerae used in this study. None of the seven MAbs showed cross-reactivity with other Vibrio spp. or closely-related V. cholerae species, V. mimicus or other gram-negative bacteria. The eighth MAbs (VC-201) specific to almost all Vibrio spp. was also obtained. In dot blotting, these MAbs can be used to detect a diluted pure culture of V. cholerae in solution with a sensitivity range of from 10(5) to 10(7) CFU ml(-1). However, the detection capability could be improved equivalent to that of PCR technique after preincubation of samples in alkaline peptone water (APW). Thus, these MAbs constitute convenient immunological tools that can be used for simple, rapid and simultaneous direct detection and differentiation of the individual serotypes of V. cholerae in complex samples, such as food and infected animals, without the requirement for bacterial isolation or biochemical characterization.

Detection of ctx gene positive non-O1/non-O139 V. cholerae in shrimp aquaculture environments

Water and post-larvae samples from black tiger (Penaeus monodon) shrimp hatcheries; pond water, pond sediment and shrimp from aquaculture farms were screened for the presence of V. cholerae. A V. cholerae-duplex PCR method was developed by utilizing V. cholerae species specific sodB primers and ctxAB genes specific primers. Incidence of V. cholerae was not observed in shrimp hatchery samples but was noticed in aquaculture samples. The incidence of V. cholerae was higher in pond water (7.6%) than in pond sediment (5.2%). Shrimp head (3.6%) portion had relatively higher incidence than shrimp muscle (1.6%). All the V. cholerae isolates (n = 42) belonged to non-O1/non-O139 serogroup, of which 7% of the V. cholerae isolates were potentially cholera-toxigenic (ctx positive). All the ctx positive V. cholerae (n = 3) were isolated from the pond water. Since, cholera toxin (CT) is the major contributing factor for cholera gravis, it is proposed that the mere presence of non-O1/non-O139 V. cholerae need not be the biohazard criterion in cultured black tiger shrimp but only the presence of ctx carrying non-O1/non-O139 V. cholerae may be considered as potential public health risk.

Putative virulence genes of Vibrio cholerae from seafoods and the coastal environment of Southwest India

Shrimp, clam and oysters were obtained at two fish markets and at a fish landing dock, and plankton, water and sediment samples were obtained from four river estuaries, in southern India. The samples were analyzed for Vibrio cholerae by conventional isolation techniques and by polymerase chain reaction (PCR) procedures. V. cholerae was isolated from 2 of 5 shrimp, 2 of 5 clam and 5 of 20 water samples. All biochemically confirmed isolates of V. cholerae were positive for toxR. For direct detection of V. cholerae in enrichment broths, PCR was performed using lysates from 0 and 6 h enrichments. All the V. cholerae isolates and enrichment broth lysates were subjected to PCR analysis for the detection of the genes toxR, ctxA, tcpA, ompU, hly, ace, Nag-ST (stn/sto), and ompU. Enrichment broths of all the samples which yielded V. cholerae were positive for toxR, OmpU and hlyA genes, while one of a fresh fish market sample was positive for the ace gene. Choleragenic V. cholerae were absent from all environmental samples and fresh fish from the markets, but one sample of shrimp was positive for V. cholerae O139.

Genetic diversity of toxigenic and nontoxigenic Vibrio cholerae serogroups O1 and O139 revealed by array-based comparative genomic hybridization

Toxigenic serogroups O1 and O139 of Vibrio cholerae may cause cholera epidemics or pandemics. Nontoxigenic strains within these serogroups also exist in the environment, and also some may cause sporadic cases of disease. Herein, we investigate the genomic diversity among toxigenic and nontoxigenic O1 and O139 strains by comparative genomic microarray hybridization with the genome of El Tor strain N16961 as a base. Conservation of the toxigenic O1 El Tor and O139 strains is found as previously reported, whereas accumulation of genome changes was documented in toxigenic El Tor strains isolated within the 40 years of the seventh pandemic. High phylogenetic diversity in nontoxigenic O1 and O139 strains is observed, and most of the genes absent from nontoxigenic strains are clustered together in the N16961 genome. By comparing these toxigenic and nontoxigenic strains, we observed that the small chromosome of V. cholerae is quite conservative and stable, outside of the superintegron region. In contrast to the general stability of the genome, the superintegron demonstrates pronounced divergence among toxigenic and nontoxigenic strains. Additionally, sequence variation in virulence-related genes is found in nontoxigenic El Tor strains, and we speculate that these intermediate strains may have pathogenic potential should they acquire CTX prophage alleles and other gene clusters. This genome-wide comparison of toxigenic and nontoxigenic V. cholerae strains may promote understanding of clonal differentiation of V. cholerae and contribute to an understanding of the origins and clonal selection of epidemic strains.