Antimicrobial profile of non-typhoidal Salmonella isolated from raw sewage in the Metropolitan Region of São Paulo, Brazil

Abstract

Introduction: Non-typhoidal Salmonella (NTS), are frequently found in sewage and are one of the main causes of diarrhea in developed and developing countries due to poor sanitation conditions. In addition, NTS can potentially act as reservoirs and vehicles for the transmission of antimicrobial resistance (AMR), which can be facilitated by the discharge of sewage effluents into environmental matrices. This study aimed to analyze a NTS Brazilian collection, focusing on their antimicrobial susceptibility profile and the presence of clinically relevant AMR-encoding genes.

Methodology: Forty-five non-clonal NTS strains from serotypes Salmonella enteritidis (n = 6), Salmonella enterica serovar 1,4,[5],12:i:- (S. 1,4,[5],12:i:-) (n = 25), Salmonella cerro (n = 7), Salmonella typhimurium (n = 3) and Salmonella braenderup (n = 4) were studied. Antimicrobial susceptibility testing was done using the Clinical and Laboratory Standards Institute guidelines (2017) and genes encoding resistance to beta-lactams, fluoroquinolones and aminoglycosides were identified by polymerase chain reaction and sequencing.

Results: Resistance to β-lactams, fluoroquinolones, tetracyclines and aminoglycosides was frequent. The highest rates were observed for nalidixic acid (89.0%), followed by tetracycline (67.0%), ampicillin (67.0%), amoxicillin + clavulanic acid (64.0%); ciprofloxacin (47.0%) and streptomycin (42.0%). The AMR-encoding genes detected were qnrB, oqxAB, blaCTX-M and rmtA.

Conclusions: Raw sewage has been considered a valuable tool to evaluate epidemiological population patterns and this study supports the view that NTS with pathogenic potential and resistance to antimicrobials are circulating in the studied region. This is worrisome due to the dissemination of these microorganisms throughout the environment.

Keywords: AMR; NTS; non-typhoidal Salmonella; sewage.