In vitro efficacy of aquaculture antimicrobials and genetic determinants of resistance in bacterial isolates from tropical aquaculture disease outbreaks.

This article focuses on the in vitro efficacy and antimicrobial resistance (AMR) gene profiles of seven fish pathogenic species isolated from Indian aquaculture disease outbreaks against four aquaculture antimicrobials: oxytetracycline, florfenicol, oxolinic acid, and enrofloxacin. The study found that Aeromonas veronii exhibited the highest resistance (45%), followed by Streptococcus agalactiae (40%), while Vibrio harveyi and Vibrio alginolyticus showed no resistance. Florfenicol was effective against all isolates, and resistance phenotypes and AMR gene prevalence were generally low, with tetA, tetB, tetC, tetM genes associated with oxytetracycline resistance and qnrS linked to quinolone resistance. These findings support the use of A. veronii as an indicator for AMR monitoring in aquaculture and provide critical data for responsible antimicrobial use to sustain fish health and minimize resistance development in Indian marine and estuarine aquaculture systems.