ABSTRACT
The objective of this study was to investigate the evolution of antibiotic resistance phenotypes, antibiotic resistance genes (ARGs) and Class 1 integron of Salmonella in municipal wastewater treatment plants (WWTPs). A total of 221 Salmonella strains were isolated from different stages of three WWTPs. After the susceptibility testing, high frequency of resistance was observed for tetracycline (TET, 47.5% of isolates) and sulfamethoxazole (SMZ, 38.5%), followed by ampicillin (AMP, 25.3%), streptomycin (STP, 17.6%), chloramphenicol (CHL, 15.4%), and gentamicin (GEN, 11.3%). Low prevalence of resistance was detected for norfloxacin (0.45%), ciprofloxacin (0.9%), and cefotaxime (0.9%). The tetA and sul3 genes were most frequently detected among the Salmonella isolates. Statistically significant correlations among AMP, CHL, GEN, and STP resistances were observed. High detection frequencies of Class 1 integron were observed in double antibiotic-resistant and multiple-antibiotic-resistant (MAR) Salmonella, which were 94.3% and 85.7%, respectively. The proliferation of MAR Salmonella and transfer of ARGs occurred in WWTPs. Class 1 integron plays a crucial role in the evolution of MAR Salmonella during WWTPs.