Ozone inactivation and attachment of Listeria monocytogenes to abiotic surfaces

The use ozone at a level of 0.25 ppm in dH₂O and phosphate buffered saline on six different strains of L. monocytogenes showed that there were differences in sensitivities between these listerial strains. After 14 minutes of ozone exposure, log CFU/mL reductions between these six strains ranged from 5.3 log CFU/mL to complete inactivation. When L. monocytogenes SLCC 5764 and 10403S were subjected to 1.0 ppm ozone, there was complete inactivation after 1.5 minutes.; Mid-exponential and late stationary phase cells were more sensitive to ozone than early stationary phase cells. Results of ozonation at different temperatures showed that 4°C was the most effective for inactivating L. monocytogenes when compared to ozonation at 24 and 37°C.; Ozonating (1.00 ppm) the microbial load on cabbage resulted in 69 and 79% log CFU/mL decrease in total plate counts after two and five minutes of exposure, respectively. Results suggested that ozone at 1.00 ppm for five minutes was effective in inactivating all L. monocytogenes cells and in reducing the total microbial counts.; Ozonation of L. monocytogenes 10403S attached to stainless steel chips showed complete inactivation after 10 minutes of 2 ppm ozone which was over a 5 log CFU/chip reduction. When cells were inoculated into evaporated milk and dried over the stainless steel chips, there was nearly a 3 log CFU/chip reduction after 2 ppm ozone exposure for 10 minutes.; L. monocytogenes 104035 and LO28 wild-type strains showed motility when gown at both 24 and 37°C although flagellin production was reduced during growth at 37°C. Both the wild-types and flagella minus mutants showed similar cells counts when attached over time on polystyrene microtiter plates and on stainless steel when gown at 24 and 37°C under static and shaking conditions. This suggests that flagella production in L. monocytogenes was not necessary for attachment and biofilm development. Scanning Electron Micrograph observations of L. monocytogenes gown on stainless steel chips for 24 hours and four days showed many cell aggregates formed on the surface, however no matrix of exopolymeric substances was seen.