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Improving the enrichment procedure for Enterobacteriaceae detection


Weber, C. Improving the enrichment procedure for Enterobacteriaceae detection. 2009, University of Zurich, Vetsuisse Faculty.

Abstract

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.

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.

Additional indexing

Item Type:Dissertation
Referees:Stephan R, Fanning S
Communities & Collections:05 Vetsuisse Faculty > Institute of Food Safety and Hygiene
Dewey Decimal Classification:570 Life sciences; biology
610 Medicine & health
Language:English
Date:2009
Deposited On:15 Jan 2010 14:51
Last Modified:05 Apr 2016 13:38
Number of Pages:8
Free access at:Related URL. An embargo period may apply.
Related URLs:http://opac.nebis.ch/F/?local_base=NEBIS&con_lng=GER&func=find-b&find_code=SYS&request=005873491

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