Salmonella spp
The genus Salmonella, belonging to the Enterobacteriaceae family, includes Gram-negative
bacteria which have both a respiratory and fermentative metabolism of carbohydrates. The
cultural methods for the isolation and detection of salmonellain food are well established.
Regulation (EC) No.2073/2005 for microbiological criteria in foodstuff reports that the
salmonella must be absent in 25 g and the analysis must be performed on 5 sampling units by
means of the EN/ISO 6579 reference method. This method currently involves nonselective
pre-enrichment in buffered peptone water followed by selective enrichment in Rappaport
21Vassiliadis Soya Broth and Muller-Kauffmann tetrathionate/novobiocin broth followed by
selective plating of these on xylose lysine deoxycholate agar (XLD) and one other selective
agar of the laboratory’s choice. Any suspect salmonella strains that are isolated are be
confirmed by biochemical and serological test methods.
The ISO method has not been fully validated for S. Typhi and S. Paratyphi and so, if these
species are of specific interest, it is presently advisable to subculture the buffered peptone
water to selenite broth as an additional selective enrichment, followed by plating on Bismuth
Sulphite agar.