Molecular Epidemiology of Multidrug-Resistant, Biofilm-Producing Vibrio parahaemolyticus from a Brackish water Aquaculture-Estuarine Interface.
Vibrio parahaemolyticus represents a contaminant of emerging concern in coastal aquaculture ecosystems, where antibiotic residues associated with intensive shrimp farming can drive the co-selection of antimicrobial resistance (AMR), virulence, and environmental persistence. The Vedaranyam Canal in Tamil Nadu, India, forms a critical interface linking estuarine ecology, brackishwater aquaculture, and seafood supply chains. In this study, 356 confirmed V. parahaemolyticus isolates recovered from canal water (n = 165), shrimp farm pond shrimp (n = 102), and retail seafood shrimp (n = 89) were subjected to comprehensive phenotypic and molecular characterization. Antimicrobial susceptibility testing revealed a high prevalence of multidrug resistance (80.6%), with multiple antibiotic resistance (MAR) indices ranging from 0.16 to 0.96; pond shrimp isolates exhibited the greatest resistance burden. Elevated resistance frequencies were observed against penicillin (97%), methicillin (91%), erythromycin (84%), and norfloxacin (82%). Virulence gene screening showed universal detection of toxR and tlh, whereas tdh and trh were detected in 15.2% and 7.3% of isolates, respectively. Among AMR determinants, tetA (41.6%), blaTEM (39.6%), and sul1 (34.3%) predominated. Biofilm formation was detected in 77.0% of isolates, including 12.6% strong biofilm producers, while efflux pump activity was observed in 41.0%. Significant associations were identified between strong biofilm formation and MDR phenotype (OR = 6.2, p < 0.001), and between efflux pump activity and MDR (OR = 4.8, p < 0.001). Seasonal prevalence increased during summer and monsoon periods and showed a positive correlation with temperature (r = 0.45, p < 0.05). These findings identify the Vedaranyam canal-aquaculture continuum as a hotspot for AMR dissemination and persistence, highlighting the need for integrated One Health surveillance.