UC Davis

Shrimp is one of the most consumed seafood products globally. Antimicrobial drugs play an integral role in disease mitigation in shrimp and other aquaculture settings to meet production demand, but their prevalent use in these industries raises public health concerns about the emergence and spread of antimicrobial resistant microorganisms. Vibrio spp., as the most common causative agents of seafood-borne infections in humans and illness in shrimp, and Enterococcus spp., as an indicator organism, are focal bacteria of interest for the monitoring of antimicrobial resistance (AMR) in seafood. In this study, 400 samples of retail shrimp meat were collected from randomly selected grocery stores in the Greater Sacramento, California, area between September 2019 and June 2020, and were tested for Vibrio spp. and Enterococcus spp. The prevalence of Vibrio and Enterococcus in these samples were 60.25% (241/400) and 89.75% (359/400), respectively. Subsamples of confirmed Vibrio and Enterococcus isolates (n = 110 each) were subjected to antimicrobial susceptibility testing (AST) using the NARMS Gram-negative and Gram-positive drug panels, respectively. Results from AST indicated that Vibrio isolates had high phenotypic resistance to ampicillin (52/110, 47.27%) and cefoxitin (39/110, 35.45%). Enterococcus were most frequently resistant to lincomycin (106/110, 96.36%), quinupristin-dalfopristin (96/110, 87.27%), ciprofloxacin (93/110, 84.55%), linezolid (86/110, 78.18%), erythromycin (58/110, 52.73%), and chloramphenicol (43/110, 39.09%). Multidrug resistance (resistance to ≥3 drug classes) was observed in 8.18% of Vibrio isolates (9/110) and 93.64% of Enterococcus isolates (103/110). No significant differences in the prevalence of AMR (P > 0.05) were found between isolates from farm raised and wild caught shrimp (P = 1.0), nor between isolates from shrimp of domestic and imported origin (P = 1.0) in Vibrio isolates. Similarly, Enterococcus isolates from wild caught shrimp samples were no different from those raised in farms (P = 0.377), and those of domestic origin were not statistically different from those that were imported (P = 0.321). Whole genome sequencing (WGS) of a subset of Vibrio isolates (n = 42) speciated isolates as primarily V. metschnikovii (24/42; 57.14%) and V. parahaemolyticus (12/42; 28.57%), and detected 27 unique antimicrobial resistance genes (ARGs) across these isolates, most commonly qnrVC6 (19.05%, 8/42), dfrA31 (11.90%, 5/42), dfrA6 (9.5%, 4/42), qnrVC1 (9.5%, 4/42). Additionally, WGS predicted phenotypic resistance in Vibrio isolates with an overall sensitivity of 11.54% and specificity of 96.05%.