Title : Effects of chilling methods for bacterial recovery and reducing bacteria on pork

To date, very little information exists on recovery methods for freeze-injured cells and the effect of blastor conventional-chilling for reducing specific pathogens associated with pork surfaces. To address these issues, two separate studies were conducted to determine 1) an effective recovery method for freeze-injured Listeria monocytogenes, Salmonella Typhimurium and Campylobacter coli associated with pork surfaces and to use this recovery method to 2) determine the effect of blastversus conventional-chilling methods for reducing pathogens at two bacterial levels (high and low) associated with skin-on and skin-off pork surfaces. In the first study, cell suspensions of L. monocytogenes, S. Typhimurium or C. coli or cells associated with pork surfaces were subjected to a freezethaw cycle (-15oC, 24 h; 4oC, 4 h). Following treatments, freeze-injured cells were plated onto media incorporating the following recovery methods: overlay (OV); thin agar layer (TAL); or Lutri plate (LP) method. The recovery rates for the pathogens using the TAL, OV and LP methods following freeze treatments in cell suspensions or on pork surfaces were not statistically different (P>0.05) from recovery rates associated with nonselective media. The results also demonstrated that OV and TAL were reliable and consistent recovery methods for isolation of freeze-injured cells. The TAL method was not only easier to perform, but also allowed for improved isolation of single colonies for further biochemical and serological characterization.