Hospital effluents into urban sewage and their influence on the development of antibiotic-resistant bacteria

With the advances in the production of new medicines, an increase in their distribution and use in healthcare facilities is inevitable. Medicine and metabolite residues are excreted and sent to the sewage. Thus, hospital effluents are of concern as they concentrate these contaminants in wastewater. It is important to emphasize that, in general, urban sewage treatment plants are not designed for high removal efficiencies of micropollutants. This study aimed to assess the adequacy of conventional methods as indicators of operational efficiency in three treatment plants to determine if they are enough to decrease bacterial-resistant phenotypes (RP) during the treatment process. We conducted four samplings at three sewage treatment plants, including those receiving effluents from a Hospital do Amor in Barretos (Brazil). Two main indicators were used: (1) traditional methodology involving physicochemical parameters and elemental analysis of solids, and (2) identification of microorganisms and antimicrobial susceptibility. Results show that when considering the conventional approach based on physicochemical evaluation, little hospital influence was observed on these indicators. However, when examining antimicrobial susceptibility, we remarked that hospital sewage affected the spread of RP in samples collected in the wastewater treatment plants (WWTP) III and IV. During autumn, winter, spring, and summer, WWTP III presented mean RP proportions around 57%, 42%, 50%, and 60%, and WWTP IV 60, 54, 34, and 41%, respectively. The WWTP II, which has received only urban sewage, showed lower mean values (46, 36, 66, and 50%, respectively). Although a direct relationship between the type of treatment and antimicrobial susceptibility was not identified, it was observed that neither treatment (stabilization pond or activated sludge) effectively reduces microbial resistance. The results raise concerns from a public health perspective and underscore the need for incorporating new protocols for analyzing sanitary effluents and the WWTP’s increased efficiency regarding the medicines.