Cytotoxic and cell vacuolating activity of Vibrio fluvialis isolated from paediatric patients with diarrhoea

Vibriosis in South Asia: A systematic review and meta-analysis

OBJECTIVES

South Asia remains home to foodborne diseases caused by the Vibrio species. We aimed to compile and update information on the epidemiology of vibriosis in South Asia.

METHODS

For this systematic review and meta-analysis, we searched PubMed, Web of Science, EMBASE, and Google Scholar for studies related to vibriosis in South Asia published up to May 2023. A random-effects meta-analysis was used to estimate the pooled isolation rate of non-cholera-causing Vibrio species.

RESULTS

In total, 38 studies were included. Seven of these were case reports and 22 were included in the meta-analysis. The reported vibriosis cases were caused by non-O1/non-O139 V. cholerae, V. parahaemolyticus, V. fluvialis, and V. vulnificus. The overall pooled isolation rate was 4.0% (95% confidence interval [CI] 3.0-5.0%) in patients with diarrhea. Heterogeneity was high (I2 = 98.0%). The isolation rate of non-O1/non-O139 V. cholerae, V. parahaemolyticus, and V. fluvialis were 9.0 (95% CI 7.0-10.0%), 1.0 (95% CI 1.0-2.0%), and 2.0 (95% CI: 1.0-3.0%), respectively. Regarding V. parahaemolyticus, O3:K6 was the most frequently isolated serotype. Cases peaked during summer. Several studies reported antibiotic-resistant strains and those harboring extended-spectrum beta-lactamases genes.

CONCLUSIONS

This study demonstrates a high burden of infections caused by non-cholera-causing Vibrio species in South Asia.

Epidemiologic potentials and correlational analysis of Vibrio species and virulence toxins from water sources in greater Bushenyi districts, Uganda

Adequate water supply is one of the public health issues among the population living in low-income settings. Vibriosis remain a significant health challenge drawing the attention of both healthcare planners and researchers in South West districts of Uganda. Intending to clamp down the disease cases in the safest water deprive locality, we investigated the virulent toxins as contaminants and epidemiologic potentials of Vibrio species recovered from surface waters in greater Bushenyi districts, Uganda. Surface water sources within 46 villages located in the study districts were obtained between June and October 2018. Standard microbiological and molecular methods were used to analyse samples. Our results showed that 981 presumptive isolates retrieved cell counts of 10-100 CFU/g, with, with (640) 65% confirmed as Vibrio genus using polymerase chain reaction, which is distributed as follows; V. vulnificus 46/640 (7.2%), V. fluvialis 30/594 (5.1), V. parahaemolyticus 21/564 (3.7), V. cholera 5/543 (0.9), V. alginolyticus 62/538 (11.5) and V. mimicus 20/476 (4.2). The virulence toxins observed were heat-stable enterotoxin (stn) 46 (82.10%), V. vulnificus virulence gene (vcgCPI) 40 (87.00%), extracellular haemolysin gene {vfh 21 (70.00)} and Heme utilization protein gene {hupO 5 (16.70)}. The cluster analysis depicts hupO (4.46% n = 112); vfh (18.75%, n = 112); vcgCPI and stn (35.71%, & 41.07%, n = 112). The principal component analysis revealed the toxins (hupO, vfh) were correlated with the isolate recovered from Bohole water (BW) source, while (vcgCPI, stn) toxins are correlated with natural raw water (NRW) and open springs (OS) water sources isolates. Such observation indicates that surface waters sources are highly contaminated with an odds ratio of 1.00, 95% CI (70.48-90.5), attributed risk of (aR = 64.29) and relative risk of (RR = 73.91). In addition, it also implies that the surface waters sources have > 1 risk of contamination with vfh and > six times of contamination with hupO (aR = 40, - 66). This is a call of utmost importance to the population, which depends on these water sources to undertake appropriate sanitation, personal hygienic practices and potential measures that ensure water quality.

A critical role for hemolysin in Vibrio fluvialis-induced IL-1β secretion mediated by the NLRP3 inflammasome in macrophages

Vibrio fluvialis causes human diarrhea, but the pathogenesis is not well-studied. We hypothesized that V. fluvialis-secreted hemolysin (VFH) may induce IL-1β secretion through the activation of the NLRP3 inflammasome and contribute to the pathogenicity of V. fluvialis. To examine this possibility, we constructed VFH mutant and complement strains and demonstrated that V. fluvialis-induced IL-1β production and cytotoxicity in human monocytic THP-1 cells and mouse macrophages is attributed to VFH. To evaluate the role of VFH in vivo, we infected adult C57BL/6 mice intraperitoneally and suckling C57/B6 mice orally with various strains. The mice treated with 10⁸ CFU wild-type V. fluvialis or cell-free supernatant containing VFH induced significantly higher IL-1β production in peritoneal lavage fluid or in colon compared with those infected with the mutant strain, while no effect on TNF and IL-6 production was observed at day 5 or 24 h post-infection. VFH contributed to pathological changes and IL-1β release independent of colonization of V. fluvialis in the colon. VFH has no effect on the synthesis of pro-IL-1β, but rather it triggers the processing of pro-IL-1β into IL-1β. Furthermore, using deficient mouse strains, we verified that V. fluvialis-induced IL-1β is mediated through activation of Caspase-1 and the NLRP3 inflammasome ex vivo. Confocal microscopy suggests that VFH contributes to cathepsin B release. Furthermore, V. fluvialis-induced IL-1β secretion requires potassium (K⁺) efflux and reactive oxygen species production. Our results provide new evidence for the role of VFH in the activation of the NLRP3 inflammasome and pathogenesis in response to V. fluvialis infection.

Summary Sentence:Vibrio fluvialis-secreted hemolysin induces IL-1β secretion through the activation of the NLRP3 inflammasome and contributes to the pathogenicity of V. fluvialis.

Occurrence of Vibrio pathotypes in the final effluents of five wastewater treatment plants in Amathole and Chris Hani District Municipalities in South Africa

We assessed the occurrence of Vibrio pathogens in the final effluents of five wastewater treatment plants (WWTPs) located in Amathole and Chris Hani District Municipalities in South Africa over a 12 months period between September 2012 and August 2013 using standard membrane filtration technique followed by cultivation on thiosulphate citrate-bile salts-sucrose (TCBS) agar. The identities of the presumptive Vibrio isolates were confirmed using polymerase chain reaction (PCR) including delineation into V. parahaemolyticus, V. vulnificus and V. fluvialis pathotypes. The counts of Vibrio spp. varied with months in all the study sites and ranged in the order of 10¹ and 10⁴ CFU/100mL. Vibrio distribution also showed seasonality with high counts being obtained in autumn and spring (p < 0.05). Prevalence of Vibrio spp. among the five WWTPs also differed significantly (p < 0.05). Of the 300 isolates that were confirmed as belonging to the Vibrio genus, 29% (86) were V. fluvialis, 28% (84) were V. vulnificus and 12% (35) were V. parahaemolyticus. The isolation of Vibrio pathogens from the final effluent suggests that this pathogen is in circulation in some pockets of the population and that the WWTPs under study do not efficiently remove bacterial pathogens from the wastewater and consequently are threats to public health.

Optimization of multilocus sequence analysis for identification of species in the genus Vibrio

Multilocus sequence analysis (MLSA) is an important method for identification of taxa that are not well differentiated by 16S rRNA gene sequences alone. In this procedure, concatenated sequences of selected genes are constructed and then analyzed. The effects that the number and the order of genes used in MLSA have on reconstruction of phylogenetic relationships were examined. The recA, rpoA, gapA, 16S rRNA gene, gyrB, and ftsZ sequences from 56 species of the genus Vibrio were used to construct molecular phylogenies, and these were evaluated individually and using various gene combinations. Phylogenies from two-gene sequences employing recA and rpoA in both possible gene orders were different. The addition of the gapA gene sequence, producing all six possible concatenated sequences, reduced the differences in phylogenies to degrees of statistical (bootstrap) support for some nodes. The overall statistical support for the phylogenetic tree, assayed on the basis of a reliability score (calculated from the number of nodes having bootstrap values of ≥ 80 divided by the total number of nodes) increased with increasing numbers of genes used, up to a maximum of four. No further improvement was observed from addition of the fifth gene sequence (ftsZ), and addition of the sixth gene (gyrB) resulted in lower proportions of strongly supported nodes. Reductions in the numbers of strongly supported nodes were also observed when maximum parsimony was employed for tree construction. Use of a small number of gene sequences in MLSA resulted in accurate identification of Vibrio species.

Vibrio fluvialis: an emerging human pathogen

Vibrio fluvialis is a pathogen commonly found in coastal environs. Considering recent increase in numbers of diarrheal outbreaks and sporadic extraintestinal cases, V. fluvialis has been considered as an emerging pathogen. Though this pathogen can be easily isolated by existing culture methods, its identification is still a challenging problem due to close phenotypic resemblance either with Vibrio cholerae or Aeromonas spp. However, using molecular tools, it is easy to identify V. fluvialis from clinical and different environmental samples. Many putative virulence factors have been reported, but its mechanisms of pathogenesis and survival fitness in the environment are yet to be explored. This chapter covers some of the major discoveries that have been made to understand the importance of V. fluvialis.

Synergistic effect of various virulence factors leading to high toxicity of environmental V. cholerae non-O1/ non-O139 isolates lacking ctx gene : comparative study with clinical strains

Background

Vibrio cholerae non-O1/ non-O139 serogroups have been reported to cause sporadic diarrhoea in humans. Cholera toxins have been mostly implicated for hypersecretion of ions and water into the small intestine. Though most of the V. cholerae non-O1/ non-O139 strains lack these cholera toxins, several other innate virulence factors contribute towards their pathogenicity. The environmental isolates may thus act as reservoirs for potential spreading of these virulence genes in the natural environment which may cause the emergence of epidemic-causing organisms.

Results

The environmental isolates of vibrios were obtained from water samples, zooplanktons and phytoplanktons, from a village pond in Gandhinagar, Gujarat, India. They were confirmed as Vibrio cholerae non-O1/ non-O139 using standard biochemical and serotyping tests. PCR experiments revealed that the isolates lacked ctxA, ctxB, tcpA, zot and ace genes whereas other pathogenicity genes like toxR, rtxC, hlyA, hapA and prtV were detected in these isolates. Compared with epidemic strain V. cholerae O1 El Tor N16961, culture supernatants from most of these isolates caused higher cytotoxicity to HT29 cells and higher hemolytic, hemagglutinin and protease activities. In rabbit ileal loop assays, the environmental isolates showed only 2-4 folds lesser fluid accumulation in comparison to N16961 and a V. cholerae clinical isolate IDH02365 of 2009. Pulsed Field Gel electrophoresis and Random amplification of Polymorphic DNA indicated that these isolates showed considerable diversity and did not share the same clonal lineage even though they were derived from the same water source. All the isolates showed resistance to one or more antibiotics.

Conclusion

Though these environmental isolates lacked the cholera toxins, they seem to have adopted other survival strategies by optimally utilising a diverse array of several other toxins. The current findings indicate the possibility that these isolates could cause some gastroenteric inflammation when ingested and may serve as progenitors for overt disease-causing organisms.

Evidence of a new metabolic capacity in an emerging diarrheal pathogen: lessons from the draft genomes of Vibrio fluvialis strains PG41 and I21563

BACKGROUND

Vibrio fluvialis is an emerging diarrheal pathogen for which no genome is currently available. In this work, draft genomes of two closely related clinical strains PG41 and I21563 have been explored.

RESULTS

V. fluvialis strains PG41 and I21563 were sequenced on the Illumina HiSeq 1000 platform to obtain draft genomes of 5.3 Mbp and 4.4 Mbp respectively. Our genome data reveal the presence of genes involved in ethanolamine utilization, which is further experimentally confirmed by growth analysis.

CONCLUSIONS

Combined in silico and growth analysis establish a new metabolic capacity of V. fluvialis to harvest energy from ethanolamine.

Triplex PCR assay for the rapid identification of 3 major Vibrio species, Vibrio cholerae, Vibrio parahaemolyticus, and Vibrio fluvialis

A triplex PCR assay was developed for the identification of 3 major Vibrio spp., Vibrio cholerae, Vibrio parahaemolyticus, and Vibrio fluvialis by targeting their haemolysin, haem-utilizing, and central regulatory genes, respectively. This simple, rapid, sensitive, and specific assay using cell lysates from 227 samples established its usefulness in research and epidemiology.

The virulence phenotypes and molecular epidemiological characteristics of Vibrio fluvialis in China

Background

Vibrio fluvialis is considered to be an emerging foodborne pathogen and has been becoming a high human public health hazard all over the world, especially in coastal areas of developing countries and regions with poor sanitation. The distribution of virulence factors, microbiological and molecular epidemiological features of V. fluvialis isolates in China remains to be examined.

Methods and results

PCR targeted at the virulence determinants and phenotype tests including metabolism, virulence and antibiotic susceptibility were performed. Pulsed-field gel electrophoresis (PFGE) analysis was used to access the relatedness of isolates. A strain with deletion of the arginine dihydrolase system was first reported and proved in molecular level by PCR. Virulence genes vfh, hupO and vfpA were detected in all strains, the ability to produce hemolysin, cytotxin, protease and biofilm formation varied with strains. High resistance rate to β-lactams, azithromycin and sulfamethoxazole were observed. Twenty-seven percent of test strains showed resistant to two and three antibiotics. PFGE analysis demonstrated great genetic heterogeneity of test V. fluvialis strains.

Conclusion

This study evaluated firstly the biological characteristics and molecular epidemiological features of V. fluvialis in China. Some uncommon biochemical characteristics were found. Virulence genes were widely distributed in the isolates from patient and seafood sources, and the occurrence of virulence phenotypes varied with strains. Continued and enhanced laboratory based-surveillance is needed in the future together with systematically collection of the epidemiological information of the cases or the outbreaks.

Vibrio fluvialis: an unusual enteric pathogen of increasing public health concern

In developing countries, the fraction of treated wastewater effluents being discharged into watersheds have increased over the period of time, which have led to the deteriorations of the qualities of major rivers in developing nations. Consequently, high densities of disease causing bacteria in the watersheds are regularly reported including incidences of emerging Vibrio fluvialis. Vibrio fluvialis infection remains among those infectious diseases posing a potentially serious threat to public health. This paper addresses the epidemiology of this pathogen; pathogenesis of its disease; and its clinical manifestations in humans.

Pathogenic potential of Aeromonas hydrophila isolated from surface waters in Kolkata, India

Members of the genus Aeromonas (family Aeromonadaceae) are medically important, Gram-negative, rod-shaped micro-organisms and are ubiquitous in aquatic environments. Aeromonas species are increasingly recognized as enteric pathogens; they possess several virulence factors associated with human disease, and represent a serious public health concern. In the present study, putative virulence traits of Aeromonas hydrophila isolates collected from different natural surface waters of Kolkata, India, were compared with a group of clinical isolates from the same geographical area using tissue culture and PCR assays. Enteropathogenic potential was investigated in the mouse model. Of the 21 environmental isolates tested, the majority showed cytotoxicity to HeLa cells (81 %), haemolysin production (71 %) and serum resistance properties (90 %), and they all exhibited multi-drug resistance. Some of the isolates induced fluid accumulation (FA ratio≥100), damage to the gut and an inflammatory reaction in the mouse intestine; these effects were comparable to those of clinical strains of A. hydrophila and toxigenic Vibrio cholerae. Interestingly, two of the isolates evoked a cell vacuolation effect in HeLa cells, and were also able to induce FA. These findings demonstrate the presence of potentially pathogenic and multi-drug-resistant A. hydrophila in the surface waters, thereby indicating a significant risk to public health. Continuous monitoring of surface waters is important to identify potential water-borne pathogens and to reduce the health risk caused by the genus Aeromonas.

Mechanism of drug resistance in a clinical isolate of Vibrio fluvialis: involvement of multiple plasmids and integrons

The role of mobile genetic elements in imparting multiple drug resistance to a clinical isolate of Vibrio fluvialis (BD146) was investigated. This isolate showed complete or intermediate resistance to all of the 14 antibiotics tested. Polymerase chain reaction (PCR) revealed the presence of a class 1 integron and the absence of the SXT element in this isolate. The strain harboured a 7.5 kb plasmid and a very low copy number plasmid of unknown molecular size. Transformation of Escherichia coli with plasmid(s) from BD146 generated two kinds of transformants, one that harboured both of these plasmids and the other that harboured only the low copy number plasmid. PCR and antibiogram analysis indicated the association of the class 1 integron with the low copy number plasmid, which also conferred all the transferable resistance traits except trimethoprim to the parent strain. A BLAST search with the sequence of the 7.5kb plasmid showed that it was 99% identical to plasmid pVN84 from Vibrio cholerae O1 in Vietnam, indicating that these two plasmids are probably one and the same. To the best of our knowledge, this is the first report of horizontal transfer of a plasmid between V. fluvialis and V. cholerae.

Identification and characterization of a repeat-in-toxin gene cluster in Vibrio anguillarum

Vibrio anguillarum is the causative agent of vibriosis in fish. Hemolysins of V. anguillarum have been considered virulence factors during infection. One hemolysin gene, vah1, has been previously identified but does not account for all hemolytic activity. The mini-Tn10Km mutagenesis performed with a vah1 mutant resulted in a hemolysin-negative mutant. The region surrounding the mutation was cloned and sequenced, revealing a putative rtx operon with six genes (rtxACHBDE), where rtxA encodes an exotoxin, rtxC encodes an RtxA activator, rtxH encodes a conserved hypothetical protein, and rtxBDE encode the ABC transporters. Single mutations in rtx genes did not result in a hemolysin-negative phenotype. However, strains containing a mutation in vah1 and a mutation in an rtx gene resulted in a hemolysin-negative mutant, demonstrating that the rtx operon is a second hemolysin gene cluster in V. anguillarum M93Sm. Reverse transcription-PCR analysis revealed that the rtxC and rtxA genes are cotranscribed, as are the rtxBDE genes. Additionally, Vah1 and RtxA each have cytotoxic activity against Atlantic salmon kidney (ASK) cells. Single mutations in vah1 or rtxA attenuate the cytotoxicity of V. anguillarum M93Sm. A vah1 rtxA double mutant is no longer cytotoxic. Moreover, Vah1 and RtxA each have a distinct cytotoxic effect on ASK cells, Vah1 causes cell vacuolation, and RtxA causes cell rounding. Finally, wild-type and mutant strains were tested for virulence in juvenile Atlantic salmon. Only strains containing an rtxA mutation had reduced virulence, suggesting that RtxA is a major virulence factor for V. anguillarum.

Phenotypic and molecular typing of Vibrio cholerae O1 and O139 isolates from India

OBJECTIVES

To determine whether Vibrio cholerae strains with similar phage types are also genetically homogeneous or heterogeneous by molecular typing methods like PFGE and RAPD-PCR employed in this study.

METHODS

A total of 26 V. cholerae O1 and O139 strains received from different parts of India were analyzed by using conventional phage typing method, antibiogram and molecular typing methods such as PFGE and RAPD-PCR.

RESULTS

Both O1 and O139 strains were resistant against two antibiotics (Ampicillin and Furazolidone) were detected. All of these strains were clustered in a single phage type, i.e., Type 27 for V. cholerae O1 and Type 1 for V. cholerae O139. Extensive molecular characterization by RAPD and PFGE showed that six sets of O1 and O139 strains, each comprising two strains, had identical PFGE and RAPD profiles. Only one O139 strain (PL-4) had unique RAPD and PFGE profile among all the 26 V. cholerae strains used in this study.

CONCLUSION

Apart from serology, the strains of V. cholerae can be discriminated by this conventional phage typing system that offers the basic information on identification, biotyping and discrimination of strains. But, a high level of heterogeneity was observed in RAPD and PFGE profiles indicating the clonal diversity of V. cholerae O1 and O139 strains. It was concluded that these strains were phenotypically identical through phage typing system and antibiogram but genetically dissimilar, as shown in molecular typing systems.