Organization of the CTX Prophage in Environmental Isolates ofVibrio mimicus

Characterization of Potential Virulence Factors of Vibrio mimicus Isolated from Fishery Products and Water

Vibrio mimicus is a Gram-negative bacterium that is closely related to V. cholerae and causes gastroenteritis in humans due to contaminated fish consumption and seafood. This bacterium was isolated and identified from 238 analyzed samples of sea water, oysters, and fish. Twenty strains were identified as V. mimicus according to amplification of the vmhA gene, which is useful as a marker of identification of the species. The production of lipases, proteases, and nucleases was detected; 45% of the strains were able to produce thermonucleases and 40% were capable of producing hydroxamate-type siderophores, and the fragment of the iuT gene was amplified in all of the V. mimicus strains. Seventy-five percent of V. mimicus strains showed cytopathic effect on Chinese hamster ovary (CHO) cells and destruction of the monolayer, and 100% of the strains were adherent on the HEp-2 cell line with an aggregative adherence pattern. The presence of virulence factors in V. mimicus strains obtained from fishery products suggests that another member of the Vibrio genus could represent a risk to the consumer due to production of different metabolites that allows it to subsist in the host.

Novel Cholera Toxin Variant and ToxT Regulon in Environmental Vibrio mimicus Isolates: Potential Resources for the Evolution of Vibrio cholerae Hybrid Strains

Atypical El Tor strains of Vibrio cholerae O1 harboring variant ctxB genes of cholera toxin (CT) have gradually become a major cause of recent cholera epidemics. Vibrio mimicus occasionally produces CT, encoded by ctxAB on CTXФ genome; toxin-coregulated pilus (TCP), a major intestinal colonization factor; and also the CTXФ-specific receptor. This study carried out extensive molecular characterization of CTXФ and ToxT regulon in V. mimicus ctx-positive (ctx ⁺) strains (i.e., V. mimicus strains containing ctx) isolated from the Bengal coast. Southern hybridization, PCR, and DNA sequencing of virulence-related genes revealed the presence of an El Tor type CTX prophage (CTX^ET) carrying a novel ctxAB, tandem copies of environmental type pre-CTX prophage (pre-CTX^Env), and RS1 elements, which were organized as an RS1-CTX^ET-RS1-pre-CTX^Env-pre-CTX^Env array. Additionally, novel variants of tcpA and toxT, respectively, showing phylogenetic lineage to a clade of V. cholerae non-O1 and to a clade of V. cholerae non-O139, were identified. The V. mimicus strains lacked the RTX (repeat in toxin) and TLC (toxin-linked cryptic) elements and lacked Vibrio seventh-pandemic islands of the El Tor strains but contained five heptamer (TTTTGAT) repeats in ctxAB promoter region similar to those seen with some classical strains of V. cholerae O1. Pulsed-field gel electrophoresis (PFGE) analysis showed that all the ctx ⁺ V. mimicus strains were clonally related. However, their in vitro CT production and in vivo toxigenicity characteristics were variable, which could be explainable by differential transcription of virulence genes along with the ToxR regulon. Taken together, our findings strongly suggest that environmental V. mimicus strains act as a potential reservoir of atypical virulence factors, including variant CT and ToxT regulons, and may contribute to the evolution of V. cholerae hybrid strains.IMPORTANCE Natural diversification of CTXФ and ctxAB genes certainly influences disease severity and shifting patterns in major etiological agents of cholera, e.g., the overwhelming emergence of hybrid El Tor variants, replacing the prototype El Tor strains of V. cholerae This report, showing the occurrence of CTX^ET comprising a novel variant of ctxAB in V. mimicus, points out a previously unnoticed evolutionary event that is independent of the evolutionary event associated with the El Tor strains of V. cholerae Identification and cluster analysis of the newly discovered alleles of tcpA and toxT suggest their horizontal transfer from an uncommon clone of V. cholerae The genomic contents of ToxT regulon and of tandemly arranged multiple pre-CTXФ^Env and of a CTXФ^ET in V. mimicus probably act as salient raw materials that induce natural recombination among the hallmark virulence genes of hybrid V. cholerae strains. This report provides valuable information to enrich our knowledge on the evolution of new variant CT and ToxT regulons.

Virulence-associated factors in Vibrio cholerae non-O1/non-O139 and V. mimicus strains isolated in ornamental fish species

During recent decades, ornamental fish have proven to be one of the fastest growing categories of pets in Europe. In this framework, we evaluated both the potential pathogenic and zoonotic risks caused by 53 Vibrio cholerae non-O1/non-O139 and a Vibrio mimicus strain isolated from ornamental fish species mostly originating from South-East Asia countries between 2000 and 2015 in Italy. All the strains were firstly identified at species level by biochemical, phylogenetic and mass spectrometry (matrix-assisted laser desorption ionization time of flight) methods, and then studied to reveal the presence of the main virulence and colonization-associated factors, as ctxA, ace, zot, stn/sto, toxR, rtxA, hlyA and tcpA by multiplex and single endpoint PCR assays. Findings showed that 21 of 54 strains harboured at least one virulence factor with a predominance for the toxR⁺ , rtxA⁺ and hlyAET⁺ genotype. Interestingly, the V. mimicus strain harboured the colonization factor and the CTX prophage receptor, tcpA, indicating the ability to capture and integrate it in its genome increasing its pathogenicity. Although these enterotoxins can sporadically cause gastroenteritis, the results highlight their probable involvement in causing severe implications for public health, suggesting the need for an European microbiological monitoring.

Serological cross-reaction between O-antigens of Shigella dysenteriae type 4 and an environmental Escherichia albertii isolate

An environmental freshwater bacterial isolate, DM104, appearing as Shigella-like colonies on selective agar plates was found to show strong and specific serological cross-reactivity with Shigella dysenteriae type 4. Biochemical identification according to the analytical profile index, molecular serotyping by restriction of the amplified O-antigen gene cluster (rfb-RFLP), together with phylogenetic analysis of the 16S rRNA gene and multi-locus sequence analysis, identified the isolate as Escherichia albertii. rfb-RFLP of DM104, revealed a profile different from that of S. dysenteriae type 4. However, western blot analysis of extracted lipopolysaccharides demonstrated strong cross-reactivity with S. dysenteriae type 4 using specific monovalent antisera and a lipopolysaccharide gel banding profile similar to that of S. dysenteriae type 4. The observed O-antigen cross-reaction between an E. albertii isolate and S. dysenteriae extends our knowledge of the extent of O-antigen cross-reaction within the Escherichia/Shigella group of organisms, and offers the possibility of using DM104 and similar cross-reacting strains as shigellosis vaccine candidates.

Detection, isolation, and identification of Vibrio cholerae from the environment

Recent molecular advances in microbiology have greatly improved the detection of bacterial pathogens in the environment. These improvements and a downward trend in the cost of molecular detection methods have contributed to increased frequency of detection of pathogenic microorganisms where traditional culture-based detection methods have failed. Culture methods also have been greatly improved, and the confluence of the two suites of methods provides a powerful tool for detection, isolation, and characterization of pathogens. While molecular detection provides data on the presence and type of pathogens, culturing methods allow a researcher to preserve the organism of interest for "-omics" studies, such as genomic, metabolomic, secretomic, and transcriptomic analysis, which are rapidly becoming more affordable. This has yielded a clearer understanding of the ecology and epidemiology of microorganisms that cause disease. In this unit, we present commonly accepted methods for isolation, detection, and characterization of V. cholerae, providing more extensive knowledge of the ecology and epidemiology of this organism. This unit has been fully revised and updated from the earlier version with the latest knowledge and additional information not previously included.

Evidence of interspecies O antigen gene cluster transfer between Shigella boydii 15 and Escherichia fergusonii

An environmental bacterial isolate, Iso10, previously found to show serological cross-reactivity with type-specific Shigella boydii 15 antisera was subjected to further molecular and serological analyses that revealed interspecies transfer of the O antigen gene cluster. Western blot analysis of Iso10 cell surface extracts and purified lipopolysaccharides demonstrated strong cross-reactivity with S. boydii 15-specific monovalent antisera and a lipopolysaccharide gel banding profile similar to that of S. boydii 15. Biochemical and phylogenetic analyses identified the Iso10 isolate as Escherichia fergusonii. O antigen gene cluster analyses of Iso10, carried out by restriction fragment length analysis of the amplified ~10-kb O antigen-encoding gene cluster, revealed a profile highly similar to that of S. boydii 15, confirming the presence of the S. boydii 15 somatic antigen in Iso10. To the best of our knowledge, this is the first report of interspecies transfer of O antigen-encoding genes between S. boydii and E. fergusonii, and it has implications for our understanding of the role of lateral gene transfer in the emergence of novel Shigella serotypes.

Detection, isolation, and identification of Vibrio cholerae from the environment

Microbiological techniques for sampling the aquatic realm have become increasingly sophisticated, especially with advances in molecular biology. These techniques have been used to detect microorganisms that cannot be cultured by conventional bacteriological methods. This has resulted in a deeper and a clearer understanding of the ecology and epidemiology of microorganisms. Important advances have been made in isolation, detection, and identification of Vibrio cholerae over the past decade. The understanding that V. cholerae, like several other pathogenic bacteria, can enter into a state known as "viable but nonculturable" (VBNC) provided important clues on the epidemiology of the pathogen and its ability to cause sudden explosive epidemics at multiple places almost simultaneously. The advances in techniques have also allowed investigators to discern the intricate aspects of the ecology of this pathogen in the aquatic world. In this unit, we present the most accepted methods for the isolation and detection of V. cholerae.