Tetracycline resistance potential of heterotrophic bacteria isolated from freshwater fin-fish aquaculture system.

Aims This study investigated the tetracycline resistance potential of heterotrophic bacteria isolated from twenty-four freshwater fin-fish culture ponds in Andhra Pradesh, India. Methods and results A total of 261 tetracycline resistant bacteria (tetR) were recovered from pond water, pond sediment, fish gills, fish intestine, and fish feed. Bacteria with high tetracycline resistance (tetHR) (n  = 30) that were resistant to tetracycline concentrations above 128  μg mL−1 were predominantly Lactococcus garvieae followed by Enterobacter spp. Lactococcus lactis, Enterobacter hormaechei, Staphylococcus arlettae, Streptococcus lutetiensis, Staphylococcus spp. Brevundimonas faecalis, Exiguobacterium profundum, Lysinibacillus spp. Stutzerimonas stutzeri, Enterobacter cloacae , and Lactococcus taiwanensis. Resistance to 1024 μg mL−1 of tetracycline was observed in L. garvieae, S. arlettae, Enterobacter spp. B. faecalis. Tet(A) (67%) was the predominant resistance gene in tetHR followed by tet(L), tet(S), tet(K) , and tet(M). At similar concentrations of exposure, tetracycline procured at the farm level (69.5% potency) exhibited lower inhibition against tetHR bacteria compared to pure tetracycline (99% potency). The tetHR bacteria showed higher cross-resistance to furazolidone (100%) followed by co-trimoxazole (47.5%) and enrofloxacin (11%). Conclusions The maximum threshold of tetracycline resistance at 1024 μg mL−1 was observed in S. arlettae, Enterobacter spp. B. faecalis , and L. garvieae and tet(A) was the major determinant found in this study. [ABSTRACT FROM AUTHOR]