PFGE subtype and antimicrobial resistance of Salmonella enteritidis isolated in Ningbo, 2003-2014

Objective To analyze the Pulsed-field gel electrophoresis(PFGE) subtype and antibiotic resistance of Salmonella enteritidis strains isolated in Ningbo, Zhejiang province, during 2003-2014, to understand the circulating features of this pathogen, and provide for the prevention and control of foodborne diseases caused by S. enteritidis. Methods PFGE patterns of 68 S. enteritidis strains were obtained following the PulseNet China protocol. The image data were analyzed by BioNumerics (Ver. 6.6). The susceptibility of the isolates to 10 antibiotics was detected by disk diffusion method. Results Overall, 68 S. enteritidis strains were subtyped into 8 PFGE patterns by Xba Ⅰ digestion, and 95.6% (65/68) of isolates shared 90% similarity. The predominant pattern JEGX01.NB0001 included 53 strains (77.9%). This pattern S. enteritidis caused 2 serious food poisoning outbreaks in 2003 and 2013 respectively, and in each outbreak, more than 80 cases were reported. The overall resistant rate was 23.5% to ampicillin, 4.4% to doxycycline, 2.9% to aztreonam, cefepime and cefotaxime, and 1.5% to chloramphenicol and trimethoprim-sulfamethoxazole. All the strains were sensitive to gentamicin, ciprofloxacin and imipenem. There were 2 multidrug resistant strains. Conclusion The study has showed a clustering trend in PFGE patterns of S. enteritidis in Ningbo. Epidemiological links were found among the clone strains causing outbreaks. Low antibiotic resistance was found through antibiotic susceptibility test, but the surveillance for multidrug resistance still needs to be strengthened.