Diversity of bacteria cultured from the blood of lesser electric rays caught in the northern gulf of Mexico.

The prevalence and taxonomic diversity of bacteria cultured from the blood of apparently healthy Lesser Electric Rays Narcine bancroftii captured from open beach habitat in the north-central Gulf of Mexico are reported herein. The blood of 9 out of 10 Lesser Electric Rays was positive for bacteria, and bacterial isolates (n = 83) were identified by 16S rRNA gene sequencing. The majority of the isolates belonged to the phylum Proteobacteria (91.5%). Vibrio spp. comprised 53% of all isolates and were recovered from all Lesser Electric Rays with culture-positive blood. Among them, V. harveyi (n = 14) and V. campbellii (n = 11) were most common, followed by a group of unidentified Vibrio sp. (n = 10) related to V. nigripulchritudo. Isolates representing other species of Proteobacteria included Pseudoalteromonas (n = 13), Shewanella (n = 5), Amphritea (n = 3), Nautella (n = 3), and Arenibacter (n = 1). Higher bacterial diversity was observed in blood cultured on marine agar relative to blood agar, but gram-positive bacteria were isolated from the latter only. The 16S rRNA gene sequences of bacterial isolates were compared phylogenetically to those from related type strains. Most isolates were identified to the level of species, but some clustered independently from reference strains, likely representing new species of Vibrio, Amphritea, Shewanella, and Tenacibaculum. The present study is the first record of any bacterium from this ray species and reveals a taxonomically and phylogenetically diverse microbiota associated with its blood. Moreover, these data document that the presence of bacteria in elasmobranch blood is not coincident with clinical signs of disease, thereby rejecting the paradigm of septicemia indicating a disease condition in aquatic vertebrates.

Prevalence and population structure of Vibrio vulnificus on fishes from the northern Gulf of Mexico.

The prevalence of Vibrio vulnificus on the external surfaces of fish from the northern Gulf of Mexico was determined in this study. A collection of 242 fish comprising 28 species was analyzed during the course of 12 sampling trips over a 16-month period. The prevalence of V. vulnificus was 37% but increased up to 69% in summer. A positive correlation was found between the percentages of V. vulnificus-positive fish and water temperatures, while salinity and V. vulnificus-positive fish prevalence were inversely correlated. A general lineal model (percent V. vulnificus-positive fish = 0.5930 - 0.02818 × salinity + 0.01406 × water temperature) was applied to best fit the data. Analysis of the population structure was carried out using 244 isolates recovered from fish. Ascription to 16S rRNA gene types indicated that 157 isolates were type A (62%), 72 (29%) were type B, and 22 (9%) were type AB. The percentage of type B isolates, considered to have greater virulence potential, was higher than that previously reported in oyster samples from the northern Gulf of Mexico. Amplified fragment length polymorphism (AFLP) was used to resolve the genetic diversity within the species. One hundred twenty-one unique AFLP profiles were found among all analyzed isolates, resulting in a calculated Simpson's index of diversity of 0.991. AFLP profiles were not grouped on the basis of collection date, fish species, temperature, or salinity, but isolates were clustered into two main groups that correlated precisely with 16S rRNA gene type. The population of V. vulnificus associated with fishes from the northern Gulf of Mexico is heterogeneous and includes strains of great virulence potential.

High numbers of Vibrio vulnificus in tar balls collected from oiled areas of the north-central Gulf of Mexico following the 2010 BP Deepwater Horizon oil spill.

The Deepwater Horizon Oil Spill was the largest oil spill in USA history releasing approximately 4.9 million barrels of crude oil into the Gulf of Mexico. Soon after the spill started, tar balls and other forms of weathered oil appeared in large numbers on beaches in Mississippi and Alabama. In this study, we analyzed tar balls for total aerobic bacterial (TAB) counts and also for the presence of Vibrio vulnificus, a human pathogen known to be abundant in the Gulf Coast environment and capable of causing severe wound infections by contact with contaminated surfaces. Our results showed that TAB counts were significantly higher in tar balls than in sand and seawater collected at the same location. In addition, V. vulnificus numbers were 10× higher in tar balls than in sand and up to 100× higher than in seawater. Densities of V. vulnificus were higher than 10(5) colony forming units/g of tar ball in all samples analyzed. Our data suggest that tar balls can act as reservoirs for bacteria including human pathogens.