Serotyping and Antibiotic Resistance Gene Characterisation of Salmonella

To investigate the serotype distribution, antimicrobial resistance (AMR) phenotypes, and resistance gene characteristics of Salmonella isolates from a hospital in Weifang, China, 80 Salmonella strains isolated from clinical specimens from January 2021 to April 2023 were collected for this study. Bacterial identification was first performed, with subsequent antimicrobial susceptibility tests. Species confirmation was validated via average nucleotide identity (ANI) analysis based on whole-genome sequencing (WGS) data, and multilocus sequence typing (MLST) was used to determine sequence types (STs). Among the 80 isolates, the most common specimen type was faeces (n=59, 73.75%), followed by blood (n=12, 15.00%). A total of 13 serotypes were identified, with Salmonella Enteritidis (n=43, 53.75%) and Salmonella 1,4,[5],12:i:- (n=11, 13.75%) as the predominant serotypes. MLST analysis identified 15 sequence types (STs), and ST11 had the highest proportion, followed by ST34. Antimicrobial susceptibility testing showed the highest resistance rate to ampicillin (80.00%), while ceftazidime exhibited the lowest resistance rate (8.75%). WGS analysis predicted 57 resistance genes, among which aminoglycoside resistance genes were the most frequent (n=16). Ten β-lactamase genes were detected, with blaTEM-1D being the most common (n=47, 58.75%). In conclusion, S. Enteritidis (primarily ST11) is the dominant serotype of Salmonella in this hospital. The isolates carry multiple resistance genes and exhibit a high resistance rate to ampicillin, emphasizing the need for cautious clinical use of this antibiotic. Ceftazidime may be a more reliable option for empirical treatment of Salmonella infections in this region.