Salmonella Contamination in Layer Farms in China: Detection and Genetic Analysis

Salmonella is the most common cause of foodborne illnesses worldwide. Poultry eggs are a major contamination source of Salmonella. The prevalence of Salmonella has been effectively reduced since a series of measures were taken to reduce contamination in egg-laying houses. In the present study, 1,512 environmental samples obtained from layer farms of different production scales were screened in a voluntary Salmonella survey study. Contaminations were detected using a PCR method. Genetic relationships among Salmonella samples were specified using molecular typing by enterobacterial repetitive intergenic consensus (ERIC)-PCR. The survey results showed that two layer farms, located in the Shandong and Hebei provinces, were contaminated with Salmonella. Thirty-one samples from these two farms, including feed, drinking nipples, egg collection belt, air inlets and outlets, air, overshoes, and eggshells, were identified as Salmonella-positive. It was observed that certain samples within the henhouses as well as in the egg collecting areas showed relatively high genetic similarities. The survey conclusively revealed minor Salmonella contamination in northern China. Moreover, various areas within the layer farms were identified as part of the propagation chain of Salmonella. Furthermore, evidence of cross-contamination of Salmonella was found in the laying houses and egg collection areas, even between these two regions. Therefore, it is necessary to establish routine Salmonella detection and subsequent environmental control measures in order to decrease the prevalence of Salmonella.