In-Vitro Studies on Antimicrobial Susceptibility and Multiple Antibiotic Resistance Profile of Vibrio parahaemolyticus Isolated from Market Shrimp in Andhra Pradesh, India

ABSTRACT
Vibrio parahaemolyticus is a halophilic, Gram-negative marine pathogen and a leading cause of seafood-associated gastroenteritis worldwide. Rising seafood consumption, together with unregulated antibiotic use in aquaculture, has driven the emergence of multidrug-resistant strains, raising both clinical and food-safety concerns. In the present study, V. parahaemolyticus was isolated from the hepatopancreas of market shrimp collected from Andhra Pradesh, India, and confirmed by a standard biochemical panel. Antimicrobial susceptibility was evaluated against nine commercially available antibiotics such as streptomycin, ampicillin, gentamycin, tetracycline, cephalexin, ciprofloxacin, neomycin, kanamycin and ceftriaxone using the agar well-diffusion method, and the minimum inhibitory concentration (MIC) of each antibiotic was determined by broth microdilution in 96-well microtiter plates. The isolate produced the largest overall zone of inhibition with ciprofloxacin (52.6 mm at 100 μg) and the smallest zone among all tested antibiotics with cephalexin (18.6 mm at 25 μg), while gentamycin produced the largest zone (29 mm) at the 25 μg concentration. Correspondingly, ciprofloxacin (7.812 μg/mL) and gentamycin (9.114 μg/mL) recorded the lowest MIC values, whereas ampicillin (333.33 μg/mL), cephalexin (250 μg/mL) and ceftriaxone (166 μg/mL) required considerably higher concentrations for inhibition, indicating comparative resistance. The multiple antibiotic resistance (MAR) index of the isolate was 0.75, well above the 0.2 threshold that flags isolates from environments with heavy antibiotic exposure. These findings confirm that V. parahaemolyticus from retail shrimp harbours resistance to several clinically and agriculturally important antibiotics and underscore the need for continued antimicrobial surveillance of seafood in this region.

Keywords: Vibrio parahaemolyticus; antimicrobial susceptibility; well diffusion assay; minimum inhibitory concentration; multiple antibiotic resistance index; shrimp.

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