Concerns have been raised regarding co-selection for antibiotic resistance among bacteria exposed to antibiotics used as growth promoters for some livestock and poultry species. Tetracycline had been commonly used for this purpose worldwide, and its residue has been associated with selection of resistant bacteria in aquatic biofilms. This study aimed to determine the resistance profile, the existence of some beta-lactamases genes and the capacity to form biofilm of bacteria isolated from water samples previously exposed to tetracycline (20 mg/L). Thirty-seven tetracycline-resistant bacterial strains were identified as Serratia marcescens, Escherichia coli, Morganella morganii, Pseudomonas aeruginosa, Citrobacter freundii, Providencia alcalifaciens, and Enterococcus faecium. The highest percentage of resistance was for ampicillin (75.75%) and amoxicillin/clavulanic acid (66.66%) in the Gram-negative bacteria and an E. faecium strain showed high resistance to vancomycin (minimum inhibitory concentration 250 μg/mL). Among the strains analyzed, 81.09% had multidrug resistance and eight Gram-negatives carried the blaOXA-48 gene. All strains were able to form biofilm and 43.23% were strong biofilm formers. This study suggests that resistant bacteria can be selected under selection pressure of tetracycline, and that these bacteria could contribute to the maintenance and spread of antimicrobial resistance in this environment.
Keywords: aquatic environment; biofilm production; carbapenemase; multidrug resistance; tetracycline.