Molecular detection of highly virulent genes and antibiogram of vibrio parahemolyticus isolated from farmed white leg shrimp

Abstract

This study investigated the molecular detection of virulence-associated genes and antibiotic resistance profiles of Vibrio parahaemolyticus isolated from farmed whiteleg shrimp (Litopenaeus vannamei) in the Mekong Delta, Vietnam. A total of 10 bacterial strains were isolated from 30 diseased shrimp postlarvae collected across multiple provinces. All isolates were identified as V. parahaemolyticus based on biochemical characterization and API 20E analysis, and further confirmed by PCR amplification of the tlh gene. Virulence gene analysis revealed the presence of vhvp-1 (362 bp) and vhvp-2 (351 bp and 303 bp) in pathogenic strains. Antibiotic susceptibility testing against 12 antibiotics showed high levels of multidrug resistance. All isolates (100%) were resistant to colistin sulfate and neomycin, while resistance rates to amoxicillin and gentamicin reached 90%, and norfloxacin 80%. In contrast, all isolates (100%) were susceptible to florfenicol, followed by ulfamethoxazole/trimethoprim (70% susceptible) and doxycycline (60% susceptible, 30% intermediate, 10% resistant). The minimum inhibitory concentration (MIC) of florfenicol ranged from 4 to 16 µg/mL, with 80% of isolates exhibiting an MIC of 4 µg/mL and 20% at 16 µg/mL. These findings highlight the widespread occurrence of multidrugresistant V. parahaemolyticus in shrimp aquaculture and confirm florfenicol as a highly effective antimicrobial candidate for disease control.