Presence of antibiotic resistance genes and its association with antibiotic occurrence in Dilúvio River in southern Brazil.

It is known that antibiotics are widely used in human and veterinary medicine. In some countries the use is controlled, however few restrictions to their use are enforced in many countries. Antibiotics and their metabolites can reach the water bodies through sewage systems, especially in those countries with partial or absent wastewater treatment systems. The overuse and misuse of antibiotics has been linked with the increase of antibiotic resistant bacteria. The relation between the occurrence of antibiotics and resistance genes in surface waters has been widely studied worldwide evincing the great importance of this subject. In this work, a methodology for quantification of 40 antibiotics of 5 different classes, in river water, by SPE-LC-MS/MS was validated. Samples were taken during a two-year period from Dilúvio River, a stream that crosses the city of Porto Alegre (RS - Brazil) and receives in nature domestic effluent. The methodology met the requirements of validation, with Limit of Quantification varying from 20 ng L-1 to 100 ng L-1. A total of 48 samples was analyzed for the presence of antibiotics for two years. From the 40 antibiotics analyzed, 8 of them (Azithromycin, Cephalexin, ciprofloxacin, clindamycin, norfloxacin, sulfadiazine, sulfamethoxazole and trimethoprim) were present in all sampling points in the range of