Vibrios associated with marine samples from the Northern Gulf of Mexico: implications for human health

Abstract

In this dissertation, I investigated the distribution and prevalence of two human-pathogenic Vibrio species (V. vulnificus and V. parahaemolyticus) in non-shellfish samples including fish, bait shrimp, water, sand and crude oil material released by the Deepwater Horizon oil spill along the Northern Gulf of Mexico (GoM) coast. In my study, the Vibrio counts were enumerated in samples by using the most probable number procedure or by direct plate counting. In general, V. vulnificus isolates recovered from different samples were genotyped based on the polymorphism present in 16S rRNA or the vcg (virulence correlated gene) locus. Amplified fragment length polymorphism (AFLP) was used to resolve the genetic diversity within V. vulnificus population isolated from fish. PCR analysis was used to screen for virulence factor genes (trh and tdh) in V. parahaemolyticus isolates yielded from bait shrimp. A series of laboratory microcosm experiments and an allele-specific quantitative PCR (ASqPCR) technique were designed and utilized to reveal the relationship between two V. vulnificus 16S rRNA types and environmental factors (temperature and salinity). In summary, research data showed that the human pathogen V. vulnificus is commonly found in non-shellfish samples (fish, bait shrimp and tar ball) of the Northern GoM coast. Moreover, I discovered a higher percentage of strains of great virulence potential in fish and shrimp than those previously reported in oysters. I proved that 16S type B strains outcompete type A strains at warmer temperatures explaining why more ii cases of vibriosis due to this pathogen occur at the end of summer. Finally, the effects of the Deepwater Horizon oil spill significantly increased the presence of V. vulnificus in beach samples. Overall, my research shows that recreational activities conducted in the Northern GoM coast have an intrinsic risk of exposure to V. vulnificus.