Posted: March 23rd, 2010 - 11:23am
Source: Journal of Food Safety

ABSTRACT
In this study, a total of 250 eggs were collected randomly from 50 retail stores in Mashhad city over a period of 3 months in the summer of 2008. Five samples from each store were collected, and transferred to the laboratory. In order to isolate Salmonella spp., conventional culture method – including pre-enrichment, enrichment, selective plating and differential plating – were performed. To confirm the identification of isolated colonies as Salmonella spp. and determining serovars as Typhimurium and Enteritidis serovars, a multiplex polymerase chain reaction assay using three pairs of primers were employed: S141 and S139 for the invA gene, specific for the genus of Salmonella; Fli15 and Tym for the fliC gene, specific for Typhimurium serovar; and Prot6e-5 and Prot6e-6 for Prot6E gene, specific for Enteritidis serovar. Four out of 250 samples (1.6%) from eggshells were determined as contaminated with Salmonella spp. Isolated colonies were confirmed as Salmonella, and their serovar was determined as Typhimurium. Salmonella spp. was not isolated from the eggs' contents.
PRACTICAL APPLICATIONS
It seems that Salmonella Typhimurium is the most prevalent serotype of egg contaminant in the Mashhad area of Iran, and the multiplex polymerase chain reaction method based on amplification from conserved genes could be a reliable alternative for conventional culture methods.