Antimicrobial Resistance, Virulence Properties and Genetic Diversity of Salmonella Typhimurium Recovered from Domestic and Imported Seafood.

The quantity of seafood imported and produced by domestic aquaculture farming has increased. Recently, it has been reported that multidrug-resistant (MDR) Salmonella Typhimurium may be associated with seafood. However, information is limited to the antimicrobial resistance, virulence properties, and genetic diversity of S. Typhimurium recovered from imported and domestic seafood. This study investigated the antimicrobial resistance, virulence properties, and genetic diversity of S. Typhimurium isolated from domestic and imported catfish, shrimp, and tilapia. A total of 127 isolates were tested for the presence of multidrug-resistance (MDR), virulence genes (invA, pagC, spvC, spvR), and genetic diversity using the Sensititre micro-broth dilution method, PCR, and pulsed-field gel electrophoresis (PFGE), respectively. All isolates were uniformly susceptible to six (amoxicillin/clavulanic acid, ceftiofur, ceftriaxone, imipenem, nitrofurantoin, and trimethoprim/sulfamethoxazole) of the 17 tested antimicrobials and genetically diverse. Fifty-three percent of the Salmonella isolates were resistant to at least one antimicrobial and 49% were multidrug resistant. Ninety-five percent of the isolates possessed the invA gene, 67% pagC, and 43% for both spvC, and spvR. The results suggest that S. Typhimurium recovered from seafood is frequently MDR, virulent, and have the ability to cause salmonellosis.

Antimicrobial and Genetic Profiles of Vibrio vulnificus and Vibrio parahaemolyticus Isolated From the Maryland Coastal Bays, United States.

Vibrio vulnificus and V. parahaemolyticus, found naturally in marine and estuarine environments, are the leading cause of seafood associated gastrointestinal illness and death. Consumption of improperly cooked crabs and handling of live crabs are potential routes of exposure to pathogenic bacteria such as V. vulnificus and V. parahaemolyticus. Little information is available on serotype genetic and antimicrobial profiles of V. vulnificus and V. parahaemolyticus recovered from Maryland estuaries. The aim of the present study was to determine the serotype of V. parahaemolyticus, evaluate antimicrobial susceptibility and genetic profiles of V. vulnificus and V. parahaemolyticus isolated from water and blue crab (Callinectes sapidus) samples collected from the Maryland Coastal Bays. One hundred and fifty (150) PCR confirmed V. parahaemolyticus including 52 tdh + (pathogenic) and 129 V. vulnificus strains were tested for susceptibility to twenty (20) different antibiotics chosen by clinical usage for Vibrio species. The O serogroups were determined using an agglutination test with V. parahaemolyticus antisera. Pulsed-field gel electrophoresis (PFGE) was used for molecular subtyping to investigate the genetic diversity among tested strains. The most prevalent serotypes were O5 (33.3%), O3 (18.7%) and O1 (14.7%). More than 41% of all tested Vibrio isolates were resistant to three or more antibiotics. Cephalothin showed the highest resistance (42% and 61%), followed by cefoxitin (42% and 31%) and ceftazidime (36% and 29%) for V. vulnificus and V. parahaemolyticus, respectively. Most strains (99-100%) were susceptible to ampicillin/sulbactam, levofloxacin, piperacillin, piperacillin/tazobactam, and tetracycline. Fifty percent (50%) of the cephalothin resistant strains were crab isolates. Vibrio vulnificus and V. parahaemolyticus isolates demonstrated a high genetic diversity and 31% of V. vulnificus and 16% of V. parahaemolyticus strains were PFGE untypeable. No correlations were found between the V. parahaemolyticus serotype, pathogenicity, genetic and antimicrobial resistance profiles of both species of Vibrio. The observed high multiple drug resistance of V. vulnificus and V. parahaemolyticus from blue crab and its environment is of public health concern. Therefore, there is a need for frequent antibiotic sensitivity surveillance for Vibrio spp.

Effect of preservatives on microbial safety and quality of smoked blue catfish (Ictalurus furcatus) steaks during room-temperature storage.

The microbial safety and quality of smoked blue catfish (Ictalurus furcatus) steaks treated with antimicrobials and antioxidants were examined during 6-week ambient storage. Five pre-smoking soaking treatments were applied: 25% NaCl and 1% ascorbic acid for 30 min or 1h, 3% sodium lactate with or without 5% rosemary extract for 30 min, and 5% sorbic acid alone for 30 min. After smoking, cooled catfish steaks were packed and analyzed at 0, 2, 4, and 6 weeks of ambient storage. Neither Listeria nor Salmonella was recovered from the smoked catfish steaks. Significant reductions (P<0.05) in total plate counts were observed in all treated samples, with those treated with 3% sodium lactate carrying the lowest microbial load. The rosemary extract-treated samples were the most stable against oxidation. All treated smoked catfish steaks had water activities less than 0.85; however, neither pH nor water activity changed significantly within each treatment group during storage (P> or 0.05). In conclusion, smoking/cooking effectively reduced microbial populations, and the use of antimicrobial agents and antioxidants, particularly 3% sodium lactate, could aid the control of microbial safety during storage, resulting in safe products for up to 6 weeks without refrigeration.