Presence of Salmonella in retail grade a eggs determined by the International Organization for Standardization 6579 method and a LightCycler polymerase chain reaction system

Abstract

This study aims to determine the presence of Salmonella in naturally contaminated grade A eggs by the standard culture method International Organization for Standardization Method 6579 (ISO) and a specific real-time PCR system (LightCycler PCR-LCPCR) to complement ISO. A total of 1635 eggs pooled into 101 samples were randomly collected within one year period from 20 different retail markets in Bursa, Turkey, carrying eggs of 16 large egg producers/suppliers of 5 cities with intensive layer production. Preparation of the egg and shell for analyses, Salmonella isolations and identifications, and detections were performed according to ISO 6887-4:2003, ISO 6579 and LCPCR, respectively. Overall Salmonella detection rate by ISO and LCPCR were 15.8 % (16/101) and 46.5 % (47/101), respectively. Out of 101 inner parts, Salmonella was detected in 11 (10.9 %) samples by ISO, and in 31 (30.7 %) samples by LCPCR. Six of 101 shell samples (5.9 %) were found to harbor Salmonella by ISO, while 18 (17.8 %) shells were positive by LCPCR. All isolates were determined as Salmonella enterica subsp. enterica serovar Enteritidis. These findings indicate considerably high Salmonella contamination in retail grade A eggs. This should be under routine monitoring by rapid methods such as PCR, complemented by standard culture to evaluate and assess the significance of risk for public health.