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ARS Home » Northeast Area » Beltsville, Maryland (BARC) » Beltsville Agricultural Research Center » Environmental Microbial & Food Safety Laboratory » Research » Research Project #428066

Research Project: Rapid Detection of E. Coli Contamination on Leafy Greens using Indole as a Sentinel Indicator

Location: Environmental Microbial & Food Safety Laboratory

Project Number: 8042-32420-006-02-S
Project Type: Non-Assistance Cooperative Agreement

Start Date: Feb 1, 2015
End Date: Dec 31, 2018

Objective:
To 1) optimize the sensitivity of indole detection; 2) calibrate indole concentrations with E. coli population densities on leafy greens; 3) assess the likelihood of leafy green contamination with non-E. coli indole producers (false positives); and 4) identify additional volatile components produced during leafy greens decomposition.

Approach:
Indole is a volatile metabolite produced by most E. coli strains. Although indole production is not exclusive to E. coli, it is still a fairly unique metabolite. Since indole is volatile, it can be absorbed onto a filter and subsequently analyzed using a novel method developed by the Cooperator. Current methods for evaluating/detecting pathogen contamination of leafy greens require maceration of small amounts of tissue followed by enrichment and detection using genetic methods and/or traditional culturing/isolation/identification. Consequently, the likelihood of detecting random contamination events is extremely low. In addition, monitoring of E. coli populations in controlled experiments is very tedious. Detection of a volatile compound such as indole allows for screening of large quantities of leafy greens over extended periods of time. Although the presence of indole is not definitive for pathogenic E. coli, it may serve as a sentinel system for identifying potential contamination events. Studies will be conducted to calibrate indole concentrations with known population densities of E. coli. In addition, other bacterial strains known to produce indole will be evaluated, as well as their prospective presence on leafy greens. Finally, the Cooperator will identify other volatile components of leafy greens decomposition which may be useful in “fingerprinting” various microbial populations.