Growth and Reduction of Bacterial Pathogens and Surrogate Microorganisms in Foods

APPROACH: Surrogates will be selected based upon published literature and isolation of resistant non-pathogens from processed foods. The resistance to processing (e.g., thermal, fermentation, etc.) of surrogates will be compared to pathogens of concern in selected food systems. Protocols for preparation of surrogates will be developed which could be used by the food industry.
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PROGRESS: 2002/05 TO 2006/04<BR>
Studies were done to determine the potential of using green fluorescent protein-labeled strains of Listeria innocua as a surrogate for L. monocytogenes for aerosol studies. Studies were conducted in a laboratory bioaerosol chamber and a pilot food processing facility. Four strains of L. innocua and 5 strains of L. monocytogenes were used. Listeria cells were released into the environment at two different cell numbers and under two different airflow conditions. Trypticase soy agar plates and oven-roasted breasts of chicken and turkey were placed on the floor to monitor Listeria cell numbers deposited from aerosols. Results revealed that L. monocytogenes and L. innocua survived equally well on chicken and turkey breast meats and TSA plates. No-fan and continuous fan applications, which affected airflow, had no significant effect on settling rates of aerosolized L. monocytogenes and L. innocua in the bioaerosol chamber, and L. innocua in the pilot plant study. Overall, L. monocytogenes and L. innocua responded similarly in aerosols in their survival and settling characteristics. Aerosol particles with diameters of 1 and 2 micrometers correlated directly with the number of Listeria cells in the aerosol, but not with particles 0.3, 0.5 and 5 micrometers in diameter. Results indicate that L. innocua could be used as a surrogate for L. monocytogenes in an aerosol study.
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IMPACT: 2002/05 TO 2006/04<BR>
Green fluorescent labeled avirulent strains of L. innocua can be used in food processing facilities and elsewhere to determine how L. monocytogenes would respond in aerosols present in the environment of processing plants.