Genetic characterization of <i>Vibrio vulnificus</i> strains isolated from oyster samples in Mexico

<div><p><i>Vibrio vulnificus</i> strains were isolated from oysters that were collected at the main seafood market in Mexico City. Strains were characterized with regard to <i>vvhA</i>, <i>vcg</i> genotype, PFGE, multilocus sequence typing (MLST), and <i>rtxA1</i>. Analyses included a comparison with <i>rtxA1</i> reference sequences. Environmental (<i>vcg</i>E) and clinical (<i>vcg</i>C) genotypes were isolated at nearly equal percentages. PFGE had high heterogeneity, but the strains clustered by <i>vcg</i>E or <i>vcg</i>C genotype. Select housekeeping genes for MLST and primers that were designed for <i>rtxA1</i> domains divided the strains into two clusters according to the E or C genotype. Reference <i>rtxA1</i> sequences and those from this study were also clustered according to genotype. These results confirm that this genetic dimorphism is not limited to <i>vcg</i> genotyping, as other studies have reported. Some environmental C genotype strains had high similarity to reference strains, which have been reported to be virulent, indicating a potential risk for oyster consumers in Mexico City.</p></div

Genetic Analysis of <i>Vibrio parahaemolyticus</i> O3:K6 Strains That Have Been Isolated in Mexico Since 1998

<div><p><i>Vibrio parahaemolyticus</i> is an important human pathogen that has been isolated worldwide from clinical cases, most of which have been associated with seafood consumption. Environmental and clinical toxigenic strains of <i>V</i>. <i>parahaemolyticus</i> that were isolated in Mexico from 1998 to 2012, including those from the only outbreak that has been reported in this country, were characterized genetically to assess the presence of the O3:K6 pandemic clone, and their genetic relationship to strains that are related to the pandemic clonal complex (CC3). Pathogenic <i>tdh</i>⁺ and <i>tdh</i>⁺/<i>trh</i>⁺ strains were analyzed by pulsed-field gel electrophoresis (PFGE) and multilocus sequence typing (MLST). Also, the entire genome of a Mexican O3:K6 strain was sequenced. Most of the strains were <i>tdh</i>/ORF8-positive and corresponded to the O3:K6 serotype. By PFGE and MLST, there was very close genetic relationship between ORF8/O3:K6 strains, and very high genetic diversities from non-pandemic strains. The genetic relationship is very close among O3:K6 strains that were isolated in Mexico and sequences that were available for strains in the CC3, based on the PubMLST database. The whole-genome sequence of CICESE-170 strain had high similarity with that of the reference RIMD 2210633 strain, and harbored 7 pathogenicity islands, including the 4 that denote O3:K6 pandemic strains. These results indicate that pandemic strains that have been isolated in Mexico show very close genetic relationship among them and with those isolated worldwide.</p></div

Comparative results between CICESE-170 and RIMD 2210633.

<p>Comparative results between CICESE-170 and RIMD 2210633.</p

<i>Vibrio parahaemolyticus</i> strains from CICESE and CAIM culture collections.

<p><i>Vibrio parahaemolyticus</i> strains from CICESE and CAIM culture collections.</p

Genetic Analysis of <i>Vibrio parahaemolyticus</i> O3:K6 Strains That Have Been Isolated in Mexico Since 1998 - Fig 1

<p>Dendrograms of CICESE and CAIM <i>V</i>. <i>parahaemolyticus</i> O3:K6 strains for: a) the neighbor-joining tree (UPGMA) by PFGE analysis after digestion with NotI and b) the neighbor-joining tree (Kimura’s 2 parameters) by MLST of the concatenated sequences of 7 loci.</p

Whole-genome comparison of CICESE-170 and RIMD 2210633, implemented in BlastDotPlot.

<p>Whole-genome comparison of CICESE-170 and RIMD 2210633, implemented in BlastDotPlot.</p

Primers used for the molecular characterization of <i>V</i>. <i>parahaemolyticus</i>.

<p>Primers used for the molecular characterization of <i>V</i>. <i>parahaemolyticus</i>.</p