Destruction of Listeria monocytogenes by Sodium Hypochlorite and Quaternary Ammonium Sanitizers

Abstract

The antimicrobial effects of two commonly used dairy plant sanitizers on Listeria monocytogenes ATCC 7644 were studied. The two sanitizers used were commercial sodium hypochlorite and quaternary ammonium compound (QAC). The effects were studied on L. monocytogenes in vitro and on stainless steel chips inoculated with the organism. Cells were exposed to concentrations of 0, 50, 100, 200, 400, and 800 ppm chlorine and QAC for 1, 2, and 5 minutes, and neutralized with tryptic soy broth. Decreases in cell numbers ranged from 3-logs to >4-logs in vitro, whereas with the stainless steel, it ranged from 1-log to >4-logs. Scanning electron microscopic (SEM) studies were done to evaluate the attachment characteristics of L. monocytogenes as compared to those of Escherichia coli on stainless steel. L. monocytogenes was found to produce a fibrous-like material similar in appearance to acidic polysaccharide fibrils produced by Pseudomonas sp., which ap-peared to be removed by the sanitizer solutions.