Detection of Integron and Antibiotic Resistance Genes of Aeromonas spp. Isolated from Freshwater Fish in Pahang, Malaysia

Aeromonas species are known as food and waterborne pathogens. This study aims to detect integrons and antibiotic resistance genes in Aeromonas spp. isolated from diseased red hybrid tilapia (Orechromis sp.), African catfish (C. gariepinus) and striped catfish (P. hypopthalmus) in Pahang, Malaysia. Samples from kidney, spleen and liver were cultured onto Rimler Shott agar to isolate the bacteria. Pathogenicity of the bacterial was observed through hemolytic activity of the bacteria on sheep blood agar. Polymerase chain reaction using specific gene was conducted for species identification. The isolates were tested for sensitivity to 14 antibiotics using the Kirby-Bauer method. Aeromonas veronii (19 isolates), A. sobria (17 isolates) and A. hydrophila (6 isolates) were isolated from freshwater fish. Interestingly, almost all (40/42) isolates showed β-hemolysis on sheep blood agar which indicates early pathogenicity. The frequencies of resistance were observed against ampicillin (69%), neomycin (52%), oxytetracycline (48%), streptomycin (48%), nalidixic acid (40%), tetracycline (36%), kanamycin (17%), chloramphenicol (10%), sulfamethoxazole (10%), nitrofurantoin (7%), gentamicin (5%) and doxycycline (2%). Multiple Antibiotic Resistance (MAR) index for the bacterial isolates was found to range from 0.14 to 0.57. Three out of 42 isolates contain integron class 1. MAR index indicated that the farmed fish in these areas might have been indiscriminately and continuously exposed to the tested antibiotics during its culture stages. Regular monitoring should be carried out to gather more information on antibiotic sensitivity of Aeromonas spp. Furthermore, increasing the resistance of Aeromonads to oxytetracycline will also pose a challenge in the treatment of Aeromonas infection.