To understand the distribution, serotype, and drug resistance of Salmonella in domestic sewage in Jining city, and to analyze the whole genome sequencing so as to provide scientific basis for the prevention and control of Salmonella.

From February to March in 2023, two samples of sewage from the intake of 3 urban sewage plants with 500 ml each were collected continuously for 7 weeks. A total of 42 sewage samples were collected for culture, isolation, and identification of Salmonella. The isolated Salmonella was tested for serum agglutination test and fluorescent quantitative PCR serotyping. In total 41 strains of Salmonella were tested for minimum inhibitory concentration (MIC) of 17 drugs in 9 classes by microbroth dilution method, followed by genome sequencing and phylogenetic analysis.

The isolation rate of Salmonella from domestic sewage in Jining city was high. Among 24 positive samples, 41 strains of Salmonella were isolated, belonging to 9 serotypes, mainly S. Agona and S. Kentucky. Liying and Jidong sewage treatment plants had their own unique serotypes. Only one strain of S. Give was not resistant, and the other 40 strains of Salmonella were multi-drug resistant. The resistance rates to sulfamethoxazole, tetracycline, ampicillin, and streptomycin were more than 90%, and the resistance rate to ampicillin/sulbactam was more than 80%. There were 19 kinds of drug resistance spectra, of which SXT-TET-STR-AMP-AMS ranked the first place. The resistance spectra of different serotypes of Salmonella were different. S. Kentucky, S. Gold Coast, and S. Infant were multi-drug resistant seriously. The resistance spectrum of the same serotype was also inconsistent in different sewage plants, and the resistance was the most serious in Liying sewage plant. The CARD database was used to predict drug resistance genes, mainly predicting 18 drug resistance genes in 8 types of drug resistance families, and the drug resistance phenotypes and drug resistance genes were almost all consistent. The ST types of different serotypes of Salmonella were different, and ST13 S. Agona was dominant. The phylogenetic tree was divided into 6 clusters, and strains in different sewage plants were in different branches, indicating that their genomes were different and had different sources.

There are various serotypes of salmonella in domestic sewage in Jining city, suggesting that they might have exist and spread in the population. Almost all strains are multi-drug resistant bacteria, carrying resistance genes extensively. Some types of strains live persistently and distribute across regions, leading to the potential risk to population. It is necessary to carry out continuous monitor, and scientific prevention and control measures need to be formulated to control the epidemic of salmonella and the aggravation of drug resistance.