Frequency of Listeria monocytogenes and antibiotic resistant Vibrio spp. in raw, frozen shrimp

Samples of imported shrimp from China, Ecuador, and Mexico were obtained from wholesale and retail markets, and aerobic plate counts (APC) using four temperature/salinity regimes, frequency of Listeria spp. and Vibrio spp. contamination, and antibiotic resistance patterns of Vibrio spp. were determined. Significant differences in APC were observed only between country and wholesale versus retail samples. Wholesale shrimp products were consistently excellent quality with respect to APC; problems observed were at the retail level. Listeria spp. and L. monocytogenes were isolated from 16.7% and 6.7% of the samples, respectively. Vibrio spp. were present in 63.3% of the samples, more often isolated from shrimp from Mexico or China than Ecuador. The majority of isolates were identified as V. parahaemolyticus (36.7%), V. alginolyticus (26.7%), or V. vulnificus (16.7%), and 53.7% were resistent to at least one antibiotic. These data reveal frozen, raw shrimp imported from Ecuador was superior quality.