High incidence of antibiotic multi-resistant bacteria in coastal areas dedicated to fish farming.

Marine bacteria exposed to antibiotics in fish farms can acquire antimicrobial resistance by mobile genetic elements and horizontal gene transfer. A total of 872 autochthonous marine bacterial strains was isolated from samples collected from four different fish farms located at northern and southern Italian Adriatic Sea. Resistance to only tetracycline (17%) and to trimethoprim-sulfadiazine (7%) were the most frequent patterns obtained, while flumequine resistance has recorded in only 0.3% of the strains. Comparing strains isolated from coastal areas and fish farms, a significant higher incidence (4% versus 10%) of multi-resistant strains in aquaculture centers was found. Significant differences in antibiotic resistance incidence were also detected among the four fish farms due probably to different approaches in farm management and the more or less frequent use of antibiotics. Antibiotic-resistant and multi-resistant strains isolated constitute an environmental reservoir directly involved in the seafood chain and might represent a public health concern.