Prevalence of Transferable Oxytetracycline Resistance Factors in Aeromonas hydrophila in Fish Hatcheries

Abstract

The distribution of motile aeromonads and prevalence of transferable oxytetracycline resistance factors in Aeromonas hydrophila of Indian major carp and catfish hatcheries in West Bengal, India were studied. Counts of motile aeromonads in carp hatching pool water (4.23 - 4.54 log cfu ml^-1), carp larval rearing water (3.36 - 3.93 log cfu ml^-1) and catfish larval rearing water (5.41 - 5.85 log cfu ml^-1) of different hatcheries did not vary much. The motile aeromonad counts in the range of 2.81-4.28 log cfu carp larva^-1and 6.08-6.69 log cfu g^-1 catfish larvae were recorded. The sensitivity of 48 Aeromonas strains to six antibiotics was observed to be in the following descending order: gentamycin, chloramphenicol, ciprofloxacin, nitrofurantoin, oxytetracycline and co-trimoxazole. The incidence of multiple antibiotic resistance (MAR) in motile aeromonads was significantly high (p<0.05) in catfish hatcheries (95%) than in carp hatcheries (41%). The prevalence of MAR in A. hydrophila (69%) was high, but not significant (p>0.05) than in A. caviae (55%). The mutation frequency of A.hydrophila strains to oxytetracycline (25 μg ml^-1) was in the range of 6.71×10^-9- 1.60×10^-6. The oxytetracycline resistance factors of size 20.13 and 25.41 kb from A. hydrophila were transferred to Escherichia coli K12 at a frequency of 2.70×10^-6 - 5.35×10^-3. It is probable that these bacteria carrying resistant factors may be the source of spreading antibiotic resistance to other environmental and pathogenic bacteria, which share the same aquatic environment.