Motile aeromonads recovered from tilapia (Oreochromis niloticus) cultured in earthen ponds in the Philippines: assessment of antibiotic susceptibility and multidrug resistance to selected antibiotics

Abstract

A total of 177 motile Aeromonas spp., comprised of A. hydrophila (n=162) and A. sobria (n=15), isolated from the water, sediment, gills and intestines of tilapia collected from the grow-out culture earthen ponds in the Philippines were investigated for their antimicrobial susceptibility to 10 antibiotics commonly used in fish aquaculture. All motile Aeromonas spp. tested generally exhibited a very high percentage of resistance to amoxicillin (A. hydrophila: 95%; A. sobria: 100%), erythromycin (99%;100%), neomycin (83%;100%), and oxytetracycline (92%;100%), respectively. On the contrary, they showed substantial susceptibility to chloramphenicol, nitrofurantoin, doxycycline, enrofloxacin and norfloxacin. Results of the antimicrobial susceptibility testing demonstrated that 94.4% and 100% of A. hydrophila and A. sobria isolates tested were resistant to antibiotics belonging to at least 3 or more categories and therefore considered as multiple drug resistant strains. The multiple antibiotic resistance (MAR) indexing of A. hydrophila and A. sobria strains showed that they originated from high-risk sources.