Antibiotic resistance and molecular epidemiological characteristics of Salmonella Typhimurium from human in Beijing, 2008−2018

  Objective  To analyze the antibiotic resistance and molecular characteristics of Salmonella Typhimurium strains isolated from human stool samples in Beijing from 2008 to 2018.

  Methods  Biochemical detection and serum agglutination test were conducted to verify 109 strains of S. Typhimurium isolated in Beijing from 2008 to 2018 and collected by the intestinal pathogen surveillance platform. The antibiotic susceptibility test was carried out by broth method. The β-lactams, quinolones and macrolides resistant genes were detected by polymerase chain reaction (PCR). The molecular typing was conducted by pulsed-field gel electrophoresis (PFGE).

  Results  The S. Typhimurium strains isolated in Beijing were generally resistant to traditional antibiotics, and 52.29% were multidrug-resistant strains. The resistance rate to the three most important front-line antibiotics (ceftriaxone, ciprofloxacin, and azithromycin) were 21.10%, 17.43%, and 1.83% respectively. We also found that the strains were co-resistant to cephalosporins and ciprofloxacin and co-resistant to cephalosporins and azithromycin. The results of antibiotic resistance gene detection showed that the most common β-lactams gene of cephalosporin-resistant strains was bla_TEM-1, followed by bla_CTX-M-14, and bla_OXA-29 gene was firstly identified in S. Typhimurium. The gene point mutations mainly led to ciprofloxacin resistance, including gyrA, parC, and parE genes. No azithromycin resistance-related genes were detected in azithromycin-resistant strains. The results of PFGE molecular typing showed that the 109 strains could be divided into 67 bands, and a predominant band including 13 strains was found.

  Conclusion  The antibiotic resistance of S. Typhimurium strains isolated from human stool samples in Beijing was serious. The PFGE pattern showed a polymorphic distribution, and strains with the same PFGE band had a more similar antibiotic resistance spectrum. It is necessary to further strengthen the surveillance of antibiotic resistance of intestinal pathogens for the effective control of the spread of antibiotic resistance.