Enteritidis-contaminated mungo bean sprouts involved several states and caused 111 cases of illness during 2014 in the USA. Newport infections occurred during 2011 in Germany and Netherlands following the consumption of contaminated mungo bean sprouts. One of the biggest outbreak that occurred in 2011 in Germany during which more than 50 people died was due to fenugreek sprouts most likely contaminated with Shigatoxin-producing E. Moreover, sprouted seeds contaminated with enteric pathogens have been associated with many large illness outbreaks, most of which have been linked to Salmonella and STEC. Aerobic bacterial counts as high as 10 7 to 10 9 cfu/g and the presence of foodborne pathogens such as Salmonella, Shigatoxin-producing Escherichia coli (STEC), and Listeria monocytogenes have been reported in alfalfa, fenguk, and mungo bean sprouts samples collected at retail level in different countries. Although normal flora of sprouted seeds is usually not a threat to human health, contamination with foodborne pathogens can occur at many points during production subsequently leading to human infections. Since conditions during sprouting are warm (20 to 25 ☌) and humid, the sprouting process is a potent bacterial amplification step occurring shortly before the packaging and consumption. The production of sprouted seeds follows a complex path from the farm to the consumer including the production and shipping of the seeds followed by sprouting and distribution of the finished product. They are available year round and are usually consumed raw. In the last decades, sprouted seeds have become a popular food item. The use of EE-broth, although preserving and increasing the dominance of Proteobacteria, can also hamper the detection of lowly abundant Gram-negative target pathogens due to outgrowth of such organisms by the highly abundant non-target Proteobacteria genera comprising the mungo bean sprout associated background flora. By increasing the relative abundance of Firmicutes, BPW also increases the abundance of Gram-positive organisms including some that might inhibit recovery of Gram-negative pathogens. BPW enrichment leads to Firmicutes and Proteobacteria dominance, whereas EE-broth enrichment preserves Proteobacteria dominance in the mungo bean sprout samples. New insights into the microbiome associated with mungo bean sprout and how it is influenced through BPW and EE-broth-based enrichment strategies used for detecting Gram-negative pathogens were generated. Both enrichments also lead to various genus level changes within the Protobacteria and Firmicutes phyla.
BPW enrichment, however, increased Firmicutes relative abundance while decreasing Proteobacteria and Bacteroidetes levels. EE-broth enrichment of such samples preserved and increased Proteobacteria dominance while reducing Bacteroidetes and Firmicutes relative abundances. 16S rRNA sequencing revealed a mungo bean sprout microbiome dominated by Proteobacteria and Bacteroidetes.
ResultsĪssessments based on aerobic mesophilic colony counts showed similar increases in mungo bean sprout background flora levels independent of the enrichment protocol used. In this study, the microbiome of mungo bean sprouts and the impact of buffered peptone water (BPW) and Enterobacteriaceae enrichment broth (EE-broth)-based enrichment protocols on this microbiome were investigated. Knowledge about the composition of the sprout microbiome is limited. However, the high number of commensal bacteria found on sprouted seeds hampers the detection of these pathogens.
Fresh sprouted seeds have been associated with a number of large outbreaks caused by Salmonella and Shiga toxin-producing E.
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