Purpose: This study was to evaluate the efficacy of quaternary ammonia, peroxyacetic acid, sodium hypochlorite, and chlorine dioxide based sanitizers against various microbial strains utilizing a dried microbial film method to simulate realistic plant conditions and actual sanitizer applications on contaminated surfaces in operational processing plants. Each strain was dried onto Hydrophobic Grid Membrane Filters [HGMF], and employed a modified disinfectant efficacy test to be used with various biocidal sanitizers. The microbial challenge strains used were both vegetative and sporeforming bacterial pathogens, and spoilage fungi & yeasts.
Methods: The microbial strains; S. Typhimurium, S. aureus, L. monocytogenes, B. cereus, P. aeruginosa, E. coli 0157:H7, A. Niger, S. cerevisiae, P. notatum were all grown in fresh liquid culture, and suspended in 0.1% Peptone. These suspensions were diluted at a challenge range of 6 - 8 log cycles for bacteria, 5 – 6 log cycles for fungi. The suspensions were uniformly filtered and dried onto HGMF filters [IsoGrids, Neogen Corp., MI]. The inoculated filters were then exposed to the various sanitizers at set concentration levels. The sanitizers were fully neutralized with Letheen broth after a contact time dependent on the microbial strain. Upon neutralization the HGMF filters were plated onto nutrient agar obtaining complete recovery of the remaining viable cells. These exposed filters were then compared against positive control filter titers to determine log reductions.
Results: Chlorine dioxide showed the most bacterial reduction overall ranging from 4-7 logs CFU/ ml. The quaternary ammonia sanitizers showed the best per concentration at preventing fungal spore germination 4-6 log CFU/ml compared to chlorine dioxide range of 4-5 log CFU/ml. Sodium hypochlorite, peroxyacetic acid sanitizers all show to be efficacious on certain strains tested but not as broad of a reduction shown by chlorine dioxide and quaternary ammonia based sanitizers.
Significance: This real world test model enables the food processor sanitarian & food safety personnel to determine which biocides/sanitizers best fit their needs in terms of the pathogens/spoilage microbes of concern on dried films of microbes which is the most predominate challenge environment for the sanitizers in question. By using a set stock suspension of the test microbe you create the same genetic clones for your sanitizer studies over a short but workable time frame of 1-2 weeks. This provides data between replicates that has very slight experimental variability.