Genetic Distinctions among Clinical and Environmental Strains of Vibrio vulnificus

Abstract

Vibrio vulnificus causes rare but frequently fatal septicemia associated with raw oyster consumption by persons with underlying hepatic or immune system dysfunction. The virulence potential of environmental reservoirs appears widely distributed, because most strains are virulent in animal models; however, several investigations recently demonstrated genetic divergence among strains from clinical versus environmental origin at independent genetic loci. The present study used PCR to screen DNA polymorphisms in strains from environmental (n ‫؍‬ 35) or clinical (n ‫؍‬ 33) sources, and genomic relationships were determined by repetitive extragenic palindromic DNA PCR (rep-PCR) typing. Significant (P < 0.01) association was observed for typical "clinical" or "environmental" polymorphism profiles based on strain origin. Most oyster isolates (88%), including all of those with the "environmental" profile, also formed a single rep-PCR genogroup. Clinical isolates within this group did not have the typical "clinical" profile. On the other hand, clinical isolates with the typical polymorphism profile were distributed among multiple rep-PCR genogroups, demonstrating greater genetic diversity than was evident by profiling genetic polymorphisms. Wound isolates were genetically distinct from typical blood isolates by all assays. Strains from an outbreak of wound infections in Israel (biotype 3) were closely related to several U.S. strains by rep-PCR, indicating potential reservoirs of emerging disease. Strains genetically related to blood isolates appeared to be relatively rare in oysters, as only one had the "clinical" polymorphism profile or clustered by rep-PCR. However, this study was not an extensive survey, and more sampling using rep-PCR for sensitive genetic discrimination is needed to determine the virulence potential of environmental reservoirs.Vibrio vulnificus is associated with serious wound infections or frequently fatal (mortality rates are generally Ͼ50%) septicemia related to consumption of raw shellfish, particularly oysters (5, 37). The bacterium is indigenous to temperate estuaries, and prevalence in oysters and seawater approaches 100% during warmer months (25,45). Most strains isolated from environmental reservoirs appear to be as virulent as clinical strains in animal models (13,35,36,39). Also, multiple virulence factors have been proposed for V. vulnificus but are generally present in most strains and do not provide predictive value (16,36,39,50). Virulent strains are distinguished by opaque colony morphology (34, 49), which reflects expression of a protective capsular polysaccharide (CPS); however, both clinical and environmental strains are generally encapsulated (45). Thus, appropriate markers to screen the virulence potential of V. vulnificus in environmental reservoirs are not available.Recently, DNA sequence polymorphisms at individual loci discriminated isolates from clinical versus oyster origin in several independent studies. Polymorphic variants generally included two genotypes, such as types ...

Vibrio vulnificus Typing Based on Simple Sequence Repeats: Insights into the Biotype 3 Group

“…Similarly, distances between isolates of biotype 3 were rather low (average genetic distance, 0.302 Ϯ 0.197) ( Table 4) compared to the high genetic distances (average, 0.820 Ϯ 0.201) found between isolates of biotypes 1 and 2 (Table 4), demonstrating the wide genetic diversity of the latter groups. These results are consistent with previous findings revealing the low level of diversity of biotype 3 compared to biotype 1 isolates (5,7,16). Furthermore, distributions of specific alleles across the three biotypes, tested as variations in repeat number, were found to be significantly different at 10 of the tested loci (P, Ͻ0.05 for nine loci) (see Table SA3 in the supplemental material).…”

Genotype Is Correlated with but Does Not Predict Virulence of Vibrio vulnificus Biotype 1 in Subcutaneously Inoculated, Iron Dextran-Treated Mice

“…Real-time PCR of the 16S rRNA (rrn) polymorphic variants identified three major types: A, B, and hybrid AB ribotypes (11,44,57). The rrn B type was predominantly associated with clinically isolated strains, and the A and AB types were associated with environmentally derived strains.…”

“…DNA polymorphism at the vcg locus, detected by a simple PCR method, identified vcgC versus vcgE genotype strains predominantly associated with clinical or environmental isolation, respectively (48). vcg typing generally matched rrn typing (11,16,49). Bisharat et al (4,5) used multilocus sequence typing (MLST) of housekeeping genes to type 159 V. vulnificus strains and constructed an online database for V. vulnificus MLST (http://pubmlst.org /vvulnificus/).…”

“…Furthermore, most lineage 1 strains possessed a genomic island that was absent from most lineage 2 strains examined in that study. Repetitive extragenic palindromic DNA PCR (rep-PCR), which is based on polymorphisms at numerous loci (56), was applied to the analysis of 68 strains that were divided into seven groups (11). Most clinical isolates were in three groups, and most environmental isolates were in one group.…”

Occurrence of clinical genotype Vibrio vulnificus in clam samples in Mangalore, Southwest coast of India

“…Genotyping based on molecular techniques, such as Pulsed-field gel electrophoresis, ribotyping, RAPD-PCR, extragenomic palindromic DNA PCR (Arias et al 1998;Chatzidaki-Livanis et al 2006); multilocus sequence typing (Bier et al 2013;Bisharat et al 2005;Cohen et al 2007;Reynaud et al 2013) and comparative genome analysis (Morrison et al 2012) have shown that V. vulnificus populations could be divided into two genotypes, the C-or the E-type. The C-type has been correlated to clinical origin responsible for human infections, while the E-type to those isolated from environmental origin and considered non-pathogenic.…”