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A differential medium, "Cronobacter" screening broth, has been designed to complement agars based on hydrolysis of chromogenic ␣-glucopyranoside substrates. The broth was evaluated using 329 Enterobacteriaceae strains (229 target isolates), spiked/naturally contaminated samples, and a parallel comparison with current methods for raw materials, line/end products, and factory environment samples.

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The current ISO standard method for detection of Enterobacteriaceae (21528-1:2004) includes enrichment in EE broth, which has been shown to be inhibitory to some members of this family, notably Cronobacter spp. A shortened procedure omitting the EE broth has been proposed, however competition from Gram-positive flora may be detrimental to the effective recovery of low levels of target organisms in some sample matrices. In this study we investigated novel cost effective modifications, designed to improve ISO 21528-1:2004 for the detection of Enterobacteriaceae. Initial experiments used a worse-case scenario involving stressed Enterobacteriaceae strains known to grow poorly in laboratory media as well as representative background competitors from powdered milk. The interaction between the Enterobacteriaceae and their competitors was characterised and additives to enhance the growth of target strains over non-target strains were investigated. Supplementation of BPW with 40 µM 8 hydroxyquinoline, 0.5g L-1 ammonium iron(III) citrate, 0.1 g L-1 sodium deoxycholate and 0.1g L-1 sodium pyruvate (BPW-S) improved the recovery of Enterobacteriaceae from artificially and naturally contaminated samples. This improvement of the pre-enrichment broth may also be of interest for methods designed to detect specific foodborne pathogens belonging to the Enterobacteriaceae (e.g. Salmonella spp., Cronobacter spp.) that require a pre-enrichment step in BPW. 19Cronobacter spp. A shortened procedure omitting the EE broth has been proposed, however competition from 20Gram-positive flora may be detrimental to the effective recovery of low levels of target organisms in some 21 sample matrices. In this study we investigated novel cost effective modifications, designed to improve ISO