title: Effects of different media on the enrichment of low numbers of Shiga toxin-producing Escherichia coli in mung bean sprouts and on the development of the sprout microbiome.
abstract: Sprouted seeds have been implicated in a number of serious outbreaks caused by Salmonella and Shiga toxin-producing Escherichia coli. Sprouts pose a very complex challenge to bacterial pathogen enrichment and detection since they naturally contain high levels of background microflora including members of the Enterobacteriaceae. As such, the currently used method cannot ensure reliable detection of STEC in sprouts. In this study, we compared different media for the enrichment of Enterobacteriaceae in their ability to promote the growth of stressed STEC at 37°C and 42°C. Mung bean sprouts were spiked with low levels of STEC and their growth was recorded over time. In addition, the microbiome of mung bean sprouts was analysed before and after enrichment. Our results indicate that the growth of dry-stressed STEC is comparable in all of the tested enrichment media except for mTSB+Novobiocin and not influenced by the incubation temperature. Low levels of STEC spiked into the sprouts resuspended in media only grew to levels of around 4logcfu/ml during enrichment, which could reduce the probability of detection. Proteobacteria was the dominant phylum detected within the microbiome of non-enriched mung bean sprouts. During enrichment in EE-broth, Proteobacteria remained the most abundant phylum. In contrast, during enrichment in BPW the relative abundance of Proteobacteria decreased whereas Firmicutes increased when compared to the non-enriched mung bean sprout microbiome. The microbiome composition was not significantly influenced by the incubation temperature during enrichment in both BPW and EE-broth. This is the first study to examine the microbiome on sprouted mung bean seeds during BPW and EE enrichment and relates the bacterial community composition changes to the enrichment of pathogens.
authors.affiliation: Institute for Food Safety and Hygiene, Vetsuisse Faculty University of Zurich, CH-8057 Zurich, Switzerland.
authors.forename: H
authors.initials: H
authors.lastname: Margot
authors.affiliation: Institute for Food Safety and Hygiene, Vetsuisse Faculty University of Zurich, CH-8057 Zurich, Switzerland.
authors.forename: T
authors.initials: T
authors.lastname: Tasara
authors.affiliation: Laboratory of Food Microbiology, Wageningen University, 6700 AA Wageningen, the Netherlands.
authors.forename: M H
authors.initials: MH
authors.lastname: Zwietering
authors.affiliation: European Chair in Food Safety Microbiology, Wageningen University, 6700 AA Wageningen, the Netherlands; Imdea Food Institute, E-28049 Madrid, Spain.
authors.forename: H
authors.initials: H
authors.lastname: Joosten
authors.affiliation: Institute for Food Safety and Hygiene, Vetsuisse Faculty University of Zurich, CH-8057 Zurich, Switzerland. Electronic address: stephanr@fsafety.uzh.ch.
authors.forename: R
authors.initials: R
authors.lastname: Stephan
mesh_terms: D058491:Bacterial Load; D003470:Culture Media / Q000494:pharmacology*; D000068536:Bacillota / Q000254:growth & development / Q000302:isolation & purification*; D005516:Food Microbiology; D064307:Microbiota; D020560:Proteobacteria / Q000254:growth & development / Q000302:isolation & purification*; D036226:Seedlings / Q000382:microbiology*; D054323:Shiga-Toxigenic Escherichia coli / Q000254:growth & development / Q000302:isolation & purification*; D000070658:Vigna / Q000382:microbiology*
chemical_list: D003470:Culture Media
keywords: Background flora; Incubation temperature; Microbiome analysis; STEC; Selective compound