Integration of Vibrio vulnificus into Marine Aggregates and Its Subsequent Uptake by Crassostrea virginica Oysters

Abstract

Marine aggregates are naturally forming conglomerations of larvacean houses, phytoplankton, microbes, and inorganics adhered together by exocellular polymers. In this study, we show in vitro that the bacterial pathogen Vibrio vulnificus can be concentrated into laboratory-generated aggregates from surrounding water. We further show that environmental (E-genotype) strains exhibit significantly more integration into these aggregates than clinical (C-genotype) strains. Experiments where marine aggregates with attached V. vulnificus cells were fed to oysters (Crassostrea virginica) resulted in greater uptake of both C and E types than nonaggregated controls. When C-and E-genotype strains were cocultured in competitive experiments, the aggregated E-genotype strains exhibited significantly greater uptake by oyster than the C-genotype strains. Vibrio vulnificus is a Gram-negative, halophilic bacterium capable of causing gastroenteritis, wound infections, and fatal septicemia in humans (1-3). It is routinely found in waters of estuarine environments as part of the normal microflora, as well as in oysters and other shellfish inhabiting those estuaries (3). V. vulnificus infection is the leading cause of seafood-borne deaths in the United States, usually resulting from the consumption of raw or undercooked oysters (3). Infections caused by ingestion commonly result in primary septicemia, almost always require hospitalization, and have a fatality rate of greater than 50% (3, 4). Wound infections usually result from exposure of open wounds to seawater containing the bacterium and can progress to fatal necrotizing fasciitis (5, 6).V. vulnificus exhibits high genotypic and phenotypic variation (3) and is divided into two genotypes, a difference originally discovered by randomly amplified polymorphic DNA PCR analysis of strains from both clinical and environmental sources (7). In this classification system, a gene designated vcg (virulence-correlated gene) was found to have two variations (8). One allele (vcgC) correlates highly with strains obtained from clinical sources and is designated the C genotype, while the other (vcgE) is correlated with environmentally isolated strains and is designated the E genotype (7,8).Over 95% of infections resulting in septicemia caused by V. vulnificus involve the consumption of raw oysters, with the remainder arising from ingestion of steamed oysters and clams (3). While millions of people in the United States eat raw oysters (9), if a consumer is afflicted with a predisposing condition, such as liver impairment or immune system dysfunction (10), the risk for infection increases 80-fold (11). Even considering these two facts, it is surprising that there are only ca. 40 primary septicemia cases reported per year (10). Usually, oysters predominately contain the E-genotype strains of V. vulnificus, which is likely a factor in the low number of infections (12-18).A study comparing the population dynamics of the V. vulnificus genotypes revealed an interesting phenomenon. While Warner and Oliver (...

Role of Anaerobiosis in Capsule Production and Biofilm Formation in Vibrio vulnificus

“…This exposure to anaerobiosis in the environment, and the prevalence of E-genotypes in oysters as well as the water column, may result in the differences between Cand E-genotype numbers of V. vulnificus (74). Our lab has previously shown an innate difference in expression levels of type IV pili aerobically (54), and these results further validate those findings as well as expound upon this under conditions lacking oxygen.…”

Variability of planktonic and epiphytic vibrios in a coastal environment affected by <em>Ostreopsis</em> blooms

“…Tamplin et al 1990, Neogi et al 2012. However, in some recent studies both free-living lifestyles or communities associated with aggregates have been reported for Vibrio (Lyons et al 2007, Froelich et al 2013, Szabo et al 2013. A second hypothesis of our study is therefore that Vibrio is found more in particles than free-living in plankton.…”

“…Vibrios have been detected on a large variety of biological surfaces, especially animals (Thompson et al 2004, Baffone et al 2006, Main et al 2015, and are also associated with various types of organic particles of non-animal origin (Lyons et al 2007, Froelich et al 2013. Recently, there has been evidence that vibrios can remain free-living (Mourino-Perez et al 2003, Worden et al 2006, Eiler et al 2006, although little is known on the factors determining whether they remain free-living versus particle-attached (Takemura et al 2014).…”

The Biology of Vibrio vulnificus

“…10%). We recently reported that if V. vulnificus cells are allowed to incorporate into marine aggregates ("snow") and then added to oyster tank water, the efficiency of uptake is greatly increased, and C-/E-genotype differences are seen (77).…”