Molecular Detection of Shigella spp. Contamination in Ready-to-Eat Salad Samples in West of Tehran

Background: Shigella bacteria can infect human body by taking contaminated food and water and are transmitted from person to person. Human body is the only natural host for these bacteria. Objective: The aim of this study was to detect Shigella contamination in pre-packed samples of salads at restaurants in western regions of Tehran city using PCR method. Methods: To conduct this research, 90 samples were purchased from the restaurants during the period of June to November 2016. The samples were cut into very small pieces, homogenized and a 25g portion of these samples was added to 225 ml of Shigella broth media containing novobiocin and incubated for 24 hours. Then DNA of cultured samples was extracted using DNPTM kit (CinnaGen, Iran) and PCR method was optimized for amplification of 613 bp segment of ipaH gene and performed on extracted DNA of all samples (before and after enrichment in Shigella broth). Results: Shigella contamination was detected in 7(7.8%) and 20(22.2%) of the tested samples before and after the enrichment, respectively. Conclusion: The results showed the contamination with Shigellabacteria in remarkable percentage of the samples and revealed the necessity of more attention and supervision in the processes of production and distribution of pre-packed salads. Besides, the findings points to the importance of enrichment in increasing the sensitivity of the PCR method to detect the bacteria in food samples.