Antibiotic Resistance in Bacterial Isolates from Commercial Probiotics Used in Aquaculture

Abstract

Aquaculture involves farming of commercially important species of finfish and shellfish. Intensification of aquaculture practices has led to many diseases of commercial importance. Probiotics are beneficial microorganisms used in aquaculture to improve the health and disease resistance of the cultured fish. It is considered as a safe alternative to antibiotics which confer resistance in the microbes when used indiscriminately. In the present study, bacterial isolates (PB-1, PB-2, PB-3, PB-4 and PB-5) from the selected commercial probiotic products used in aquaculture were assessed for their bacterial pathogen inhibition efficiency, antibiotic sensitivity and the presence of antibiotic resistance genes viz., tetK, tetL, tetM and tetO. The probiotic isolates exhibited varying levels of inhibition against the bacterial pathogens viz., Aeromonas hydrophila, Streptococcus sp., Flavobacterium columnare, Edwarsiella tarda and Vibrio alginolyticus. F.columnare was the most inhibited by all the five probiotic bacterial isolates. The antimicrobial sensitivity test showed that the isolates, PB-2, PB-3, PB-4 and PB-5 were resistant to oxytetracycline except the isolate, PB-1. The antibiotic resistant genes, tetK and tetL were found to be present in all the probiotic bacterial isolates, whereas tetM and tetO were absent in all the isolates. The results of the study showed that although probiotics exhibit inhibitory activity against the bacterial pathogens, antibiotic resistance to oxytetracycline and the presence of antibiotic resistant genes showed that they could also act as a possible source for the transfer and spread of antibiotic resistance among the microbes in the aquatic ecosystem.