Bacterial resistance to oxytetracycline in different life stages of Indian freshwater carp aquaculture system

Abstract

In India antibiotics are frequently used for preventing and controlling bacterial pathogens incarp aquaculture system, yet no studies have been performed to evaluate the ecological impact of itsintensive and prolonged use. In this work the frequency of oxytetracycline-resistant bacteria from water,palletized feed and different life stages of fish from Indian freshwater carp aquaculture system as well asthe level of resistance of selected strains was investigated. Viable as well as antibiotic-resistant bacterialcounts were performed by spread plate method in culture media supplemented with the oxytetracycline.Sixty two resistant Gram negative isolates which represented the oxytetracycline-resistant bacterialpopulation, were randomly selected on nutrient agar supplemented with oxytetracycline (50μg/ml) fromcarp farms and feed pellet samples. Among these bacterial isolates Flavobacterium (21%), Alcaligenes(14.5%), Aeromonas (11%), Pseudomonas (10%) and Enterobacteriace (19%) were the most frequent.The Escherichia, Serratia, Citrobacter, Enterobacter, Shigella and Proteus from Enterobacteriace wererecovered. Twelve isolates of oxytetracycline resistant bacteria were mainly dominated in adult fishes bythe genus Flavobacterium (23%) and Enterobacteriace(41%). Selected strains exhibited high levels ofoxytetracycline resistance with minimum inhibitory concentrations (MICs) ranging from 50 to600μg/ml.This study shows the presence of an important population of oxytetracycline-resistant bacteriain the microflora of Indian carp aquaculture farms. Therefore the environment of these farms might playimportant roles as reservoirs of bacteria carrying genetic determinants for high level tetracyclineresistance, prompting an important risk to public health.