Development of a strain-specific assay to determine viability of probiotic bacteria in cattle feed CALS Impact Statement uri icon


  • Abstract

    We developed a simple assay for detecting specific live probiotic bacteria after their application to cattle feed.


    Probiotic bacteria are economically important but poorly characterized. When added live and in high enough numbers to cattle feed, the HOFG1 strain of the probiotic bacterium Lactobacillus sp. is effective in reducing shedding of the human pathogen Escherichia coli O157:H7. This approach to controlling pathogens can greatly reduce the use of antibiotics in feed and hence the pressures that may select for antibiotic-resistant strains of pathogenic bacteria. The probiotic bacteria must be alive to be effective, however, and industrial processing of cattle feed can create environmental conditions that kill the probiotic bacteria. A method has been needed to test the level of living bacteria present in feed.


    We have developed an assay to determine approximate numbers of live probiotic bacteria in feed samples. The assay involves recovering total bacteria from samples of complex feed (silage-based, cornflake-based, etc.) and using a dilution series of those samples to inoculate a medium that selectively enhances the growth of the probiotic strain. These cultures are then assayed using PCR to detect the presence of the specific probiotic strain.


    This assay provides processors with a means to monitor the viability of a specific strain of probiotic bacteria and ensure that an adequate dose is applied to feed. The assay provides quality assurance to feedlot customers that the proper dosage of live bacteria is on the feed. This assay has been used to identify problems at two feedlots where the application of the probiotic bacteria to feed at excessively high temperatures resulted in the loss of viable probiotic bacteria. The processing protocols at those feedlots have been corrected as a result. This approach to detecting and quantifying live bacteria in complex samples has potential agricultural, industrial, and medical applications. In livestock, it could be used to track levels of viable probiotic bacteria throughout the gastrointestinal tract.

    Funding Sources

    • Federal Formula Funds - Research (e.g., Hatch, McIntire-Stennis, Animal Health)
    • Private (e.g., commodity groups, foundations, companies)

    Key Personnel

    • Joe Flint, Graduate Student, Cornell University, Department of Microbiology