Characterization of Two Cryptic Plasmids Isolated in Haiti from Clinical Vibrio cholerae Non-O1/Non-O139

Mobile Genetic Elements of Vibrio cholerae and the Evolution of Its Antimicrobial Resistance

Vibrio cholerae (VC) is the causative agent of the severe dehydrating diarrheal disease cholera. The primary treatment for cholera is oral rehydration therapy (ORT). However, in case of moderate to severe dehydration, antibiotics are administered to reduce morbidity. Due to the emergence of multidrug resistant (MDR) strains of VC routinely used antibiotics fail to be effective in cholera patients. Antimicrobial resistance (AMR) is encoded in the genome of bacteria and is usually acquired from other organisms cohabiting in the environment or in the gut with which it interacts in the gut or environmental niche. The antimicrobial resistance genes (ARGs) are usually borne on mobile genetic elements (MGEs) like plasmids, transposons, integrons and SXT constin. Horizontal gene transfer (HGT) helps in the exchange of ARGs among bacteria leading to dissemination of AMR. In VC the acquisition and loss of AMR to many antibiotics have been found to be a dynamic process. This review describes the different AMR determinants and mechanisms of resistance that have been discovered in VC. These ARGs borne usually on MGEs have been recovered from isolates associated with past and present epidemics worldwide. These are responsible for resistance of VC to common antibiotics and are periodically lost and gained contributing to its genetic evolution. These resistance markers can be routinely used for AMR surveillance in VC. The review also presents a precise perspective on the importance of the gut microbiome in the emergence of MDR VC and concludes that the gut microbiome is a potential source of molecular markers and networks which can be manipulated for the interception of AMR in the future.

Surveillance and Genomics of Toxigenic Vibrio cholerae O1 From Fish, Phytoplankton and Water in Lake Victoria, Tanzania

The occurrence of toxigenic Vibrio cholerae O1 during a non- outbreak period in Lake Victoria was studied and genetic characteristics for environmental persistence and relatedness to pandemic strains were assessed. We analyzed 360 samples of carps, phytoplankton and water collected in 2017 during dry and rainy seasons in the Tanzanian basin of Lake Victoria. Samples were tested using PCR (ompW and ctxA) with DNA extracted from bacterial isolates and samples enriched in alkaline peptone water. Isolates were screened with polyvalent antiserum O1 followed by antimicrobial susceptibility testing. Whole genome sequencing and bioinformatics tools were employed to investigate the genomic characteristics of the isolates. More V. cholerae positive samples were recovered by PCR when DNA was obtained from enriched samples than from isolates (69.0% vs. 21.3%, p < 0.05), irrespectively of season. We identified ten V. cholerae O1 among 22 ctxA-positive isolates. Further studies are needed to serotype the remaining ctxA-positive non-O1 strains. Sequenced strains belonged to El Tor atypical biotype of V. cholerae O1 of MLST ST69 harboring the seventh pandemic gene. Major virulence genes, ctxA, ctxB, zot, ace, tcpA, hlyA, rtxA, ompU, toxR, T6SS, alsD, makA and pathogenicity islands VPI-1, VPI-2, VSP-1, and VSP-2 were found in all strains. The strains contained Vibrio polysaccharide biosynthesis enzymes, the mshA gene and two-component response regulator proteins involved in stress response and autoinducers for quorum sensing and biofilm formation. They carried the SXT integrative conjugative element with phenotypic and genotypic resistance to aminoglycoside, sulfamethoxazole, trimethoprim, phenicol, and quinolones. Strains contained a multidrug efflux pump component and were resistant to toxic compounds with copper homeostasis and cobalt-zinc-cadmium resistance proteins. The environmental strains belonged to the third wave of the seventh pandemic and most are genetically closely related to recent outbreak strains from Tanzania, Kenya, and Uganda with as low as three SNPs difference. Some strains have persisted longer in the environment and were more related to older outbreak strains in the region. V. cholerae O1 of outbreak potential seem to persist in Lake Victoria through interactions with fish and phytoplankton supported by the optimum water parameters and intrinsic genetic features enhancing survival in the aquatic environment.