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Evaluation of hot-water and sanitizer dip treatments of knives contaminated with bacteria and meat residue.

Hot water (HW; 82.2 degrees C, 180 degreesF) is used for sanitation of meat cutting implements in most slaughter facilities, but validation of actual practices against meat-borne bacterial pathogens and spoilage flora is lacking. Observed implement immersions in HW in two large pork processing plants were found to typically be < or = 1 s. Impact of these practices on bacteria on metal surfaces was assessed in the laboratory, and alternative treatments were investigated. Knives were inoculated with raw pork residues and Escherichia coli O157:H7, Salmonella Typhimurium DT104, Clostridium perfringens, and Lactobacillus spp. and were sampled before and after 1- or 15-s dips of blades in HW, warm water (48.9 degrees C), or warm sanitizers (neutral or acid quaternary ammonium compounds [QAC] at 400 ppm, or peroxyacetic acid at 700 ppm H2O2 and 165 ppm peroxyacetic acid). Simultaneous scrubbing and 15-s dipping in HW or acid QAC was also evaluated. Reductions on knives dipped for 1 s were usually < 1 log and were not significantly different (P > 0.05) between treatments. Reductions of E. coli O157:H7 after 15 s in HW, neutral QAC, acid QAC, or peroxyacetic acid were 3.02, 2.38, 3.04, and 1.52 log, respectively. Reductions of other bacteria due to HW were not significantly different from sanitizers and were significantly greater than warm water for all bacteria except C. perfringens. Combined scrubbing and 15-s dipping in HW resulted in a 2.91- and 2.25-log reduction of E. coli O157:H7 and Salmonella Typhimurium DT104, respectively, whereas reduction caused by acid QAC was significantly less at about 1.7 log each. Brief dip treatments of contaminated knives have limited efficacy, but longer immersions cause greater reductions that were not enhanced by scrubbing. QAC is a suitable alternative to HW in this application.