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United States Department of Agriculture

Agricultural Research Service

Research Project: MOLECULAR MICROBIOLOGY AND CONTROL OF ENTERIC PATHOGENS THAT CONTAMINATE FRESH PRODUCE Title: Effect of Enrichment Medium on Real-time Detection of Salmonella enterica from Lettuce and Tomato Enrichment Cultures

Authors
item Gorski, Lisa
item Liang, Anita

Submitted to: Journal of Food Protection
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 9, 2010
Publication Date: June 6, 2010
Citation: Gorski, L.A., Liang, A.S. 2010. Effect of Enrichment Medium on Real-time Detection of Salmonella enterica from Lettuce and Tomato Enrichment Cultures. Journal of Food Protection. 73(6):1047-1056

Interpretive Summary: Three different media were compared to determine if they affected molecular detection of Salmonella from lettuce and tomato. Three different genes of Salmonella were used as detection targets, and five epidemiologically relevant strains were tested. One medium, Tryptic Soy Broth,was the most efficient in fast detection of Salmonella from produce. This may be due to medium components as well as the interactions of the normal plant bacteria that compete for detection targets in these cultures.

Technical Abstract: vThree commonly used enrichment broths for detection of Salmonella (Buffered Peptone Water – BPW, Tryptic Soy Broth – TSB, and Universal Preenrichment Broth – UPB) were compared for use in real time SYBR Green PCR detection of Salmonella introduced into enrichment cultures made from store bought lettuce and tomatoes. The produce served as a source of normal plant microbiota to measure how well DNA-based detection methods for Salmonella work in a suspension of plant-associated bacteria that may be closely related to Salmonella. A qualitative assessment of the background microbiota that arose in the three enrichment broths from incubation of tomato and lettuce showed that different bacteria predominated in the different broths. Using five produce-related, outbreak Salmonella strains and PCR primers directed toward three different genes of Salmonella, the data suggest that the ability to detect Salmonella from these enrichment cultures by real time molecular techniques was affected by the medium and possibly the background microbiota. The data indicate that TSB was the best of the three media for real time SYBR Green detection of Salmonella. Additional testing showed that an immunomagnetic separation method may be useful in BPW and UPB, but not in TSB enrichment media. Three commonly used enrichment broths for detection of Salmonella (Buffered Peptone Water – BPW, Tryptic Soy Broth – TSB, and Universal Preenrichment Broth – UPB) were compared for use in real time SYBR Green PCR detection of Salmonella introduced into enrichment cultures made from store bought lettuce and tomatoes. The produce served as a source of normal plant microbiota to measure how well DNA-based detection methods for Salmonella work in a suspension of plant-associated bacteria that may be closely related to Salmonella. A qualitative assessment of the background microbiota that arose in the three enrichment broths from incubation of tomato and lettuce showed that different bacteria predominated in the different broths. Using five produce-related, outbreak Salmonella strains and PCR primers directed toward three different genes of Salmonella, the data suggest that the ability to detect Salmonella from these enrichment cultures by real time molecular techniques was affected by the medium and possibly the background microbiota. The data indicate that TSB was the best of the three media for real time SYBR Green detection of Salmonella. Additional testing showed that an immunomagnetic separation method may be useful in BPW and UPB, but not in TSB enrichment media.

Last Modified: 10/21/2014
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