Prevalence and antimicrobial susceptibility of major foodborne pathogens in imported seafood

Seafood is a leading commodity implicated in foodborne disease outbreaks in the United States. Seafood importation rose dramatically in the past 3 decades and now contributes to more than 80% of the total U.S. seafood supply. However, limited data are available on the microbiological safety of imported seafood. In this study, we obtained a total of 171 salmon, shrimp, and tilapia samples imported from 12 countries in three retail stores in Baton Rouge, LA. The total microbial population and the prevalence and antimicrobial susceptibilities of six major foodborne-pathogen genera (Campylobacter, Escherichia coli, Listeria, Salmonella, Shigella, and Vibrio) were determined. The aerobic plate counts (APC) for the 171 samples averaged 4.96 log CFU/g, with samples from Chile carrying the highest mean APC of 6.53 log CFU/g and fresh samples having a significantly higher mean APC than frozen ones (P < 0.0001). There were 27 samples (15.8%) with unacceptable microbiological quality (APC > 7 log CFU/g). By culture, no sample tested positive for Campylobacter coli, Shigella, or Vibrio vulnificus. Campylobacter jejuni and Salmonella enterica serovar Typhimurium were each recovered once from farm-raised tilapia from China. By PCR, 17.5 and 32.2% of the samples were positive for Salmonella and Shigella, respectively. The overall prevalence rates of other target bacteria were low, ranging from 4.1% for Listeria monocytogenes to 9.4% for E. coli. All of the Vibrio parahaemolyticus isolates recovered were from shrimp, and 63.3% showed intermediate resistance to ampicillin. Both C. jejuni isolates possessed a rare resistance to gentamicin, while 75% of L. monocytogenes isolates were resistant to nitrofurantoin. Taken together, these findings suggest potential food safety hazards associated with imported seafood and warrant further large-scale studies.