engleski

Detection of Salmonella in eggs obtained from artificially infected laying hens

Infection caused by Salmonella, associated with egg and egg products in Europe represent the majority of the reported food-borne outbreaks (EFSA and ECDC, 2012). In EU the laying flocks should be free from S. Enteritidis and S. Typhimurium, and consequently, the product itself should be free from these serotypes. A major obstacle in control of Salmonella in eggs is an apparent low number of positive eggs (EFSA, 2007 ; Chemaly et al., 2009). The aim of this investigation was to better understand the mechanism behind the low occurrence of contaminated egg and to compare detection of Salmonella by PCR and most commonly used conventional ISO-culture methods. At 18 wk of age, 60 hens were infected in two replicate trials with oral doses of approximately 109 cells of S. Enteritidis. Shedding and colonization were measured at regular time points during 6 weeks. All laid eggs were examined for Salmonella by both, ISO 6579:2002 and PCR methods. A 5’nuclease Real-Time PCR assay targeting the ttrRSBCA locus of Salmonella spp. was applied and internal amplification control was also included in reaction, as described by Malorny et al., 2004. and Kramer et al., 2011. After infection the inoculated bacteria were recovered in all hens. Despite the fact that all hens became infected, only 8 eggs shells and one egg yolk were Salmonella positive. Surprisingly, the positive eggs were shed during a very narrow time period. Direct plating methods take several days, are expensive and labor intensive, and usually can detect only high number of bacteria. Problems related to low prevalence can be minimized if more sensitive and specific detection methods are applied for which molecular method, such as PCR, have been introduced. The method was also much quicker than conventional techniques, taking less than 24 h to obtain a result. In conclusion, both literature, and our experimental investigations of contamination of eggs from positive hens have shown that the number of contaminated eggs is low, and that the PCR was superior to ISO 6579:2002.

Salmonella; eggs; PCR

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