Correlation of mannitol fermentation with virulence-associated genotypic characteristics in Vibrio vulnificus isolates from oysters and water samples in the Gulf of Mexico

Vibrio vulnificus strains (n = 469) isolated from the Gulf of Mexico oysters and waters over a period of 2 years were subjected to phenotypic and genotypic characterizations. Of the strains that could be definitively genotyped (n = 465), 58% were classified as genotype A, 29% as genotype B, and 13% as genotype A/B by 16S rRNA genotyping. When the same strain bank was characterized by virulence-correlated gene (vcg) typing, 65% were genotype E while 35% were genotype C. Further analysis focusing on strains falling into typical genotype categories (i.e., 16S rRNA types A or B, excluding type A/B strains) showed a high degree of concordance (93%) when comparing the two genotyping methods. d-Mannitol fermentation was also predictive of genotype, with an 86% agreement between 16S rRNA genotype and mannitol fermentation patterns, and an 85% agreement between vcg genotype and mannitol fermentation patterns. d-Mannitol fermentation should be considered as a simple and less expensive alternative to screen V. vulnificus isolates for virulence potential, particularly when analyzing large strain banks.