English

Abstract

In India antibiotics are frequently used for preventing and controlling bacterial pathogens in carp aquaculture system, yet no studies have been performed to evaluate the ecological impact of its intensive 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 as the level of resistance of selected strains was investigated. Viable as well as antibiotic-resistant bacterial counts were performed by spread plate method in culture media supplemented with the oxytetracycline. Sixty two resistant Gram negative isolates which represented the oxytetracycline-resistant bacterial population, were randomly selected on nutrient agar supplemented with oxytetracycline (50μg/ml) from carp 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 were recovered. Twelve isolates of oxytetracycline resistant bacteria were mainly dominated in adult fishes by the genus Flavobacterium (23%) and Enterobacteriace(41%). Selected strains exhibited high levels of oxytetracycline resistance with minimum inhibitory concentrations (MICs) ranging from 50 to 600μg/ml.This study shows the presence of an important population of oxytetracycline-resistant bacteria in the microflora of Indian carp aquaculture farms. Therefore the environment of these farms might play important roles as reservoirs of bacteria carrying genetic determinants for high level tetracycline resistance, prompting an important risk to public health.