Abstract
Antimicrobial resistance in Salmonella infections has become a growing global public health threat. This study was conducted to characterize the antibiotic resistance profiles and molecular typing characteristics of Salmonella isolates from diarrhea patients in Wanzhou district, Chongqing Municipality. A total of 66 Salmonella strains were isolated 769 from clinical samples of patients with diarrhea. Of the 11 serotypes identified, the top three were Salmonella 1,4,[5],12:i:- (n = 23), Salmonella Typhimurium (n = 17), and Salmonella Thompson (n = 8). Thirteen distinct sequence types (STs) were identified among the 66 Salmonella isolates, with ST34 (30.3%, 20/66) and ST19 (25.8%, 17/66) emerging as the predominant epidemic clones. Forty-two different antimicrobial resistance genes were identified. The aminoglycoside resistance genes aac(6’)-Iaa (n = 68, 98.48%), β-lactam resistance genes blaTEM-1B (n = 41, 62.12%), and tetracycline resistance genes tet(A) (n = 32, 48.48%) were the most predominant. The co-existence of blaCTX-M/blaCMY-2 and qnrS was found in 11 strains. Salmonella from diarrhea patients in Wanzhou district showed high resistance (54.55–77.27%) to ampicillin, tetracycline, and streptomycin. Over half (59.10%) of the isolates exhibited multidrug resistance (MDR). A total of 4 isolates (2 S. Typhimurium and 2 S. Thompson) showed resistance to both fluoroquinolones and third-generation cephalosporins. Two isolates each of S. Typhimurium and S. Thompson displayed resistance to both fluoroquinolones and third-generation cephalosporins. Point mutations leading to amino acid changes were identified in gyrA and parC genes. Core genome single-nucleotide polymorphism showed phylogenetic clustering of the isolates with the same Multilocus sequence typing or serotype. Using a threshold of 15 core-genome SNPs, we speculated that six related epidemiological events existed. These findings underscore the necessity for ongoing surveillance of MDR patterns and molecular characteristics of Salmonella, together with prudent antibiotic use, to curb further dissemination and support the development of effective prevention and control strategies.
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