Serotype distribution and drug resistance characteristics of livestock-borne Salmonella in China, 2006−2016

ObjectiveTo understand the distribution of serogroups and drug resistance of Salmonella isolates from major livestock and poultry animals in China during 2006–2016, complete the resistance data of animal-derived Salmonella and providing evidence for the prevention and control of multi-drug resistant Salmonella infection in China.

MethodsA total of 776 isolates of Salmonella from chickens and pigs were serotyped using traditional serum agglutination methods and used for drug susceptibility test to 16 antibiotics using broth microdilution method. The minimum inhibition concentration was obtained and interpreted according to standard of Clinical and Laboratory Standards Institute (2017).

ResultsForty-nine serotypes were identified in 776 Salmonella isolates. The first three serotypes were S. Enteritidis (31.57%), S. Derby (17.53%) and S. Typhimurium (14.82%). The most common serotypes of the strains from pigs and chickens were S. Derby (39.15%) and S. Enteritidis (51.62%), respectively. The resistance rate of the tested Salmonella isolates to sulfafurazole was highest (73.32%), followed by the resistance rate to streptomycin (70.88%) and nalidixic acid (69.59%). In the isolated strains, 10.70% showed resistance to ciprofloxacin, while more than 92.00% were sensitive to the third-generation cephalosporin. In addition, the resistance rate of the pig-origin strains were higher than that of chicken-origin strains (P＜0.05). Moreover, 63.40% of the tested strains showed resistance to three and more than three antibiotics. The multi-drug resistance rate of S. typhimurium was highest (90.44%), followed by that of S. Derby (63.24%) and S. Enteritidis (58.78%).

ConclusionCurrently, the multi-drug resistance of main livestock and poultry origin Salmonella strains is serious in China. The resistance level of pig-origin strains was more severe than that of chicken-origin strains. The resistance rates of the strains to most antibiotics is increasing over time. It is necessary to pay close attention to the real time surveillance for the change and spread of drug resistance of Salmonella and the potential threat to the environment and human. Importantly, our results also indicated that the rational application and supervision of antibiotic use in farmed animals need to be strengthened.