Bacterial populations from different tilapia culture system with no antimicrobial use were characterized. Concret pond and commercial feed, land pond and commercial feed, and land pond and animal manure were used in systems I, II and III, respectively. Ninety-eight bacterial strains were subjected to sensitivity testing. Members of Vibrionaceae were the most prevalent in all systems analysed. The most bacterial strains were resistant to ampicillin and erithromicin, but resistance to norfloxacin and gentamicin were uncommon. A half to bacterial isolates was resistant to tetracycline. From the 98 bacterial isolates, 96% were resistant to two or more antimicrobials. The multiple antimicrobial resistance index was determined and it was similar for all systems analyzed (Mar= 0.4), indicating a high risk source for multiple antibiotic resistance.
nile tilapia; antibiotic; bacteria; antimicrobial resistance
