100A-21 |
Simultaneous recovery of four heat-injured foodborne pathogens in an innovative Thin Agar Layer recovery system |
V. C. H. WU and D. Y. C. Fung. Department of animal sciences and industry, Kansas State University, 202 Call Hall, Manhattan, KS 66506 Recovery of injured cells is an important issue in food microbiology. We have developed and tested a one-step resuscitation Thin Agar Layer (TAL) system (non-selective agar overlaid on selective agar) to effectively recover heat-, acid-, cold-, and salt-injured foodborne pathogens in liquid foods. Each TAL unit was designed for the recovery of one injured population. This report describes the use of a four-compartment petri dish to simultaneously recover four heat-injured foodborne pathogens in the same unit to increase efficiency of the system. Into a sterile four-compartment petri dish (same size as the standard dish), four pathogen specific selective media (MSA for Escherichia coli O157:H7, MOX for Listeria monocytogenes, XLD for Salmonella typhimurium, and CIN for Yersinia enterocolitica) were first poured into each compartment individually. After solidification, 22 ml of melted TSA (48°C) was overlaid on top of all four agars and formed a continuous layer of nonselective agar. A cocktail of the four pathogens was heat injured at 55°C for 10 min. The cocktail was plated onto the TSA layer of the four-compartment unit by use of the Spiral Plating System. After incubation at 37°C for 24 hours, the colonies developed on each of the four segments were counted by virtue of specific colony morphology and color reactions. Concurrently, single pathogen TAL plates and selective agar plates of each pathogen were also tested. Duplicates of each set were tested three separate times for the comparison. Results indicated that no significant differences occurred between the single recovery unit compared with the four-compartment unit for enumeration of all four heat-injured pathogens (p>0.05). Also both TAL systems recovered higher microbial population than the respective selective media (p<0.05). Thus, the four-compartment TAL unit can be used to simultaneously recover four heat-injured pathogens and is four times more efficient than the simple TAL plate.
Session 100A, Food Microbiology: General II
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