Avaliação do impacto do lançamento do efluente tratado no rio: diversidade bacteriana e resistência antimicrobiana

Abstract

Wastewater treatment plants (WWTPs) play a crucial role in environmental preservation, as they mitigate impacts on public health and quality of life. Despite promoting the removal of various pollutants, their infrastructure is not designed for the elimination of microorganisms and micropollutants. Consequently, numerous bacterial species, as well as ARGs, antimicrobial pharmaceuticals (AMPs), and metals can persist post-treatment, exerting selective pressure and favoring the emergence of antimicrobial-resistant bacteria (ARB). This study aimed to evaluate the microbial composition of raw sewage (RS), treated sewage (TS), upstream river (UR), and downstream river (DR), and assess the phenotypic and genotypic profiles related to AMPs and metal tolerance of bacteria isolated from treated sewage. Sequencing (16S) was conducted to assess bacterial composition, and isolated bacteria were evaluated for metal tolerance on agar for zinc, copper, cadmium, mercury, and silver, and antimicrobial susceptibility testing by disk diffusion. Additionally, we searched for genetic markers of epidemiological surveillance related to AMP resistance. The results indicate that despite sharing OTUs, populations exhibit differences in their composition and correctly grouped by sample type. RS and TS samples showed differences in diversity, and UR and DR samples displayed differences in richness, suggesting that RS removes part of the bacterial population through treatment and TS however, it does not significantly alter the river's composition. Metal tolerance results indicate that the evaluated bacteria demonstrated high tolerance to copper and zinc, which can be explained by the use of these metals in bacterial metabolism. Tolerance to cadmium was intermediate, while the MICs for mercury and silver were lower, indicating the high toxicity of these metals. The highest phenotypic resistance rate in Enterobacterales was to penicillins, in Aeromonas to sulfamethoxazole/trimethoprim, in Acinetobacter to quinolones, as well as for Enterococcus, while Pseudomonas and Streptococcus showed resistance to cephalosporins. The most prevalent resistance gene in Gram-negative rods was blaIMP, followed by blaVIM and blaTEM. It is concluded that the WWTP functions as a hotspot for resistance genes and contributes to the dissemination of ARB and ARGs in the environment, and that TS contributes to changes in the DR microbial community.