Vibrio parahaemolyticus and Vibrio vulnificus Recovered from Oysters during an Oyster Relay Study.

Vibrio parahaemolyticus and Vibrio vulnificus are naturally occurring estuarine bacteria and are the leading causes of seafood-associated infections and mortality in the United States. Though multiple-antibiotic-resistant V. parahaemolyticus and V. vulnificus strains have been reported, resistance patterns in vibrios are not as well documented as those of other foodborne bacterial pathogens. Salinity relaying (SR) is a postharvest processing (PHP) treatment to reduce the abundances of these pathogens in shellfish harvested during the warmer months. The purpose of this study was to evaluate the antimicrobial susceptibility (AMS), pathogenicity, and genetic profiles of V. parahaemolyticus and V. vulnificus recovered from oysters during an oyster relay study. Isolates (V. parahaemolyticus [n = 296] and V. vulnificus [n = 94]) were recovered from oysters before and during the 21-day relaying study to detect virulence genes (tdh and trh) and genes correlated with virulence (vcgC) using multiplex quantitative PCR (qPCR). AMS to 20 different antibiotics was investigated using microbroth dilution, and pulsed-field gel electrophoresis (PFGE) was used to study the genetic profiles of the isolates. Twenty percent of V. vulnificus isolates were vcgC+, while 1 and 2% of V. parahaemolyticus were tdh+ and trh+, respectively. More than 77% of the V. vulnificus isolates and 30% of the V. parahaemolyticus isolates were resistant to at least one antimicrobial. Forty-eight percent of V. vulnificus and 8% of V. parahaemolyticus isolates were resistant to two or more antimicrobials. All isolates demonstrated a high genetic diversity, even among those isolated from the same site and having a similar AMS profile. No significant effects of the relaying process on AMS, virulence genes, or PFGE profiles of V. vulnificus and V. parahaemolyticus were observed.IMPORTANCE Analysis of the antibiotic resistance profiles of V. vulnificus and V. parahaemolyticus isolated from oysters during this study indicated that more than 48% of V. vulnificus isolates were resistant to two or more antimicrobials, including those recommended by the CDC for treating Vibrio infections. Also, the V. parahaemolyticus isolates showed high MICs for some of the Vibrio infection treatment antibiotics. Monitoring of AMS profiles of this bacterium is important to ensure optimal treatment of infections and improve food safety. Our study showed no significant differences in the AMS profiles of V. vulnificus (P = 0.26) and V. parahaemolyticus (P = 0.23) isolated from the oysters collected before versus after relaying. This suggests that the salinity of the relaying sites did not affect the AMS profiles of the Vibrio isolates, although it did reduce the numbers of these bacteria in oysters (S. Parveen et al., J Food Sci 82:484-491, 2017, https://doi.org/10.1111/1750-3841.13584).

Antibiotic resistance of Vibrio parahaemolyticus and Vibrio vulnificus in various countries: A review.

Vibrio parahaemolyticus and Vibrio vulnificus are the leading causes of seafood associated infections and mortality in the United States. The main syndromes caused by these pathogens are gastroenteritis, wound infections, and septicemia. This article reviewed the antibiotic resistance profile of V. parahaemolyticus and V. vulnificus in the United States and other countries including Italy, Brazil, Philippines, Malaysia, Thailand, China, India, Iran, South Africa and Australia. The awareness of antimicrobial resistance of these two pathogens is not as well documented as other foodborne bacterial pathogens. Vibrio spp. are usually susceptible to most antimicrobials of veterinary and human significance. However, many studies reported that V. vulnificus and V. parahaemolyticus showed multiple-antibiotic resistance due to misuse of antibiotics to control infections in aquaculture production. In addition, both environmental and clinical isolates showed similar antibiotic resistance profiles. Most frequently observed antibiotic resistance profiles involved ampicillin, penicillin and tetracycline regardless of the countries. The presence of multiple-antibiotic resistant bacteria in seafood and aquatic environments is a major concern in fish and shellfish farming and human health.

Seasonal distribution of total and pathogenic Vibrio parahaemolyticus in Chesapeake Bay oysters and waters.

The objectives of this study were to investigate the seasonal distribution of total and pathogenic Vibrio parahaemolyticus in the Chesapeake Bay oysters and waters, and to determine the degree of association between V. parahaemolyticus densities and selected environmental parameters. Oyster and water samples were collected monthly from three sites in Chesapeake Bay, Maryland from November 2004 through October 2005. During collection of samples, water temperature, salinity, turbidity, dissolved oxygen, pH, chlorophyll a, and fecal coliform levels in oysters were also determined. V. parahaemolyticus levels were enumerated by a quantitative direct-plating method followed by DNA colony hybridization; presence/absence was further determined by overnight broth enrichment followed by either standard colony isolation or real-time PCR. The thermolabile hemolysin (tlh) gene and thermostable direct hemolysin (tdh) gene were targeted for detection of total and pathogenic V. parahaemolyticus, respectively, for both direct plating and enrichment. The thermostable related hemolysin (trh) gene, which is a presumptive pathogenicity marker, was targeted only for the enrichment approach. By direct plating, colonies producing tlh signals were detected in 79% of oyster samples at densities ranging from 1.5x10(1) to 6.0x10(2) CFU/g. Pathogenic V. parahaemolyticus (tdh+) was detected in 3% (level was 10 CFU/g) of oyster samples while no V. parahaemolyticus was detected in water samples. By the enrichment approach with standard colony isolation, 67% of oyster and 55% of water samples (n=33) were positive for total V. parahaemolyticus, and all samples were negative for pathogenic V. parahaemolyticus. In contrast, enrichment followed by real-time PCR detected tlh, tdh and trh in 100%, 20% and 40% of oyster and 100%, 13% and 40% of water enrichments collected from June to October 2005, respectively. V. parahaemolyticus densities in oysters varied seasonally and were found to be positively correlated with water temperature, turbidity, and dissolved oxygen.