Efficacy of a post enrichment acid treatment for isolation of Escherichia coli O157:H7 from alfalfa sprouts

Fedio, Willis M.; Jinneman, Karen C.; Yoshitomi, Ken J.; Zapata, Rubén Antonio Vargas; Weagant, Stephen D.

doi:10.1016/j.fm.2011.12.003

Cited by 15 publications

(19 citation statements)

References 20 publications

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“…In conjunction with the use of mRBA, an acid treatment procedure was optimized to take advantage of the acid tolerance of STEC while reducing the growth of other confounding organisms (7,12,13). Our findings agree with previous reports that document the acid sensitivity of non-/;.…”

Section: Discussionsupporting

confidence: 89%

“…The use of immunomagnetic separation (IMS) using antibody-coated paramagnetic beads has been reported to increase the sensitivity and selectivity of pathogen isolation procedures (8 ,1 7 ,18). Acid treatment at pH 2 has been demonstrated to be effective in reducing background flora and enhancing target STEC recovery (7,12,13). Acid tolerance and acid resistance is regarded as an important intrinsic property of E. coli strains, thus enabling the organism to survive acidic environments such as the stomach (4,5,10).…”

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confidence: 99%

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Isolation of Shiga Toxin–Producing Escherichia coli Serogroups O26, O45, O103, O111, O121, and O145 from Ground Beef Using Modified Rainbow Agar and Post–Immunomagnetic Separation Acid Treatment

Tillman

Wasilenko

Simmons

et al. 2012

Journal of Food Protection

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It is estimated that at least 70% of human illnesses due to non-O157 Shiga toxin-producing Escherichia coli (STEC) in the United States are caused by strains from the top six serogroups (O26, O45, O103, O111, O121, and O145). Procedures for isolating STEC from food products often use plating media that include antimicrobial supplements at concentrations that inhibit background microflora growth but can also inhibit target STEC growth. In this study, an agar medium with lower supplement concentrations, modified Rainbow agar (mRBA), was evaluated for recovery of STEC serogroups O26, O45, O103, O111, O121, and O145 from ground beef enrichments. A post-immunomagnetic separation (IMS) acid treatment step was additionally used to reduce background microflora and increase recovery of target STEC strains. Ground beef samples (325 g) were artificially contaminated with STEC and confounding organisms and enriched for 15 h. Recovery of the target STEC was attempted on the enrichments using IMS and plating onto mRBA and Rainbow agar (RBA). Additionally, acid treatment was performed on the post-IMS eluate followed by plating onto mRBA. Using the combination of mRBA and acid treatment, target STEC were isolated from 103 (85.8%) of 120 of the low-inoculated samples (1 to 5 CFU/325-g sample) compared with 68 (56.7%) of 120 using no acid treatment and plating onto RBA with higher levels of novobiocin and potassium tellurite. The combination of acid treatment and mRBA provides a significant improvement over the use of RBA for isolation of STEC serogroups O26, O45, O103, O111, O121, and O145 from raw ground beef.

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Section: Discussionsupporting

confidence: 89%

mentioning

confidence: 99%

Isolation of Shiga Toxin–Producing Escherichia coli Serogroups O26, O45, O103, O111, O121, and O145 from Ground Beef Using Modified Rainbow Agar and Post–Immunomagnetic Separation Acid Treatment

Tillman

Wasilenko

Simmons

et al. 2012

Journal of Food Protection

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“…To take advantage of this feature, an acid treatment procedure to inhibit the growth of competitor organisms can be used as a preliminary selective step before the isolation. Multiple studies have shown the usefulness of this procedure (10,11,28). The observed acid tolerance in the present study was comparable to that in the study of Jasson et al (18) using the same stress conditions, but their work focused on O157:H7 strains.…”

Section: Discussionsupporting

confidence: 88%

Growth of Stressed Strains of Four Non-O157 Shiga Toxin-Producing Escherichia coli Serogroups in Five Enrichment Broths

Verhaegen¹,

Reu²,

Heyndrickx

et al. 2015

Journal of Food Protection

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The purpose of this study was to evaluate (i) the behavior of several strains of non-O157 Shiga toxin-producing Escherichia coli (STEC) serogroups (O26, O103, O111, and O145) exposed to different stress conditions and (ii) the growth dynamics of stressed and nonstressed non-O157 STEC cells in five enrichment media. STEC strains were exposed to acid, cold, and freeze stresses. Lethal and sublethal injuries were determined by plating in parallel on selective and nonselective agar media. Freeze stress (8 days, 20°C) caused the most lethal (95.3% ± 2.5%) injury, as well as the most sublethal (89.1% ± 8.8%) injury in the surviving population. Growth of stressed and nonstressed pure cultures of non-O157 STEC on modified tryptic soy broth, buffered peptone water (BPW), BPW with sodium pyruvate, Brila, and STEC enrichment broth (SEB) was determined using total viable counts. To compare growth capacities, growth after 7 and 24 h of enrichment was measured; lag phases and maximum growth rates were also calculated. In general, growth on BPW resulted in a short lag phase followed by a high maximum growth rate during the enrichment of all tested strains when using all three stress types. Furthermore, BPW ensured the highest STEC count after 7 h of growth. Supplementing the medium with sodium pyruvate did not improve the growth dynamics. The two selective media, Brila and SEB, were less efficient than BPW, but Brila's enrichment performance was remarkably better than that of SEB. This study shows that irrespective of the effect of background flora, BPW is still recommended for resuscitation of non-O157 STEC.

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“…Despite various efforts that have previously been undertaken to improve the current methods for detection of foodborne pathogens from sprouted seeds, there are various difficulties that still remain [19–22]. One drawback in particular is the lack of physiological traits that would allow the selective discrimination of target pathogens such as STEC and Salmonella from large amounts of sprout associated background flora predominated by non-target bacteria including enterobacteria species that outnumber these pathogens by several orders of magnitude.…”

Section: Discussionmentioning

confidence: 99%

Mungo bean sprout microbiome and changes associated with culture based enrichment protocols used in detection of Gram-negative foodborne pathogens

2016

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BackgroundFresh sprouted seeds have been associated with a number of large outbreaks caused by Salmonella and Shiga toxin-producing E. coli. However, the high number of commensal bacteria found on sprouted seeds hampers the detection of these pathogens. Knowledge about the composition of the sprout microbiome is limited. 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.ResultsAssessments based on aerobic mesophilic colony counts showed similar increases in mungo bean sprout background flora levels independent of the enrichment protocol used. 16S rRNA sequencing revealed a mungo bean sprout microbiome dominated by Proteobacteria and Bacteroidetes. EE-broth enrichment of such samples preserved and increased Proteobacteria dominance while reducing Bacteroidetes and Firmicutes relative abundances. BPW enrichment, however, increased Firmicutes relative abundance while decreasing Proteobacteria and Bacteroidetes levels. Both enrichments also lead to various genus level changes within the Protobacteria and Firmicutes phyla.ConclusionsNew 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. BPW enrichment leads to Firmicutes and Proteobacteria dominance, whereas EE-broth enrichment preserves Proteobacteria dominance in the mungo bean sprout samples. 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. 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.

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Efficacy of a post enrichment acid treatment for isolation of Escherichia coli O157:H7 from alfalfa sprouts

Cited by 15 publications

References 20 publications

Isolation of Shiga Toxin–Producing Escherichia coli Serogroups O26, O45, O103, O111, O121, and O145 from Ground Beef Using Modified Rainbow Agar and Post–Immunomagnetic Separation Acid Treatment

Isolation of Shiga Toxin–Producing Escherichia coli Serogroups O26, O45, O103, O111, O121, and O145 from Ground Beef Using Modified Rainbow Agar and Post–Immunomagnetic Separation Acid Treatment

Growth of Stressed Strains of Four Non-O157 Shiga Toxin-Producing Escherichia coli Serogroups in Five Enrichment Broths

Mungo bean sprout microbiome and changes associated with culture based enrichment protocols used in detection of Gram-negative foodborne pathogens

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