Inactivation of Bacillus anthracis spores by liquid biocides in the presence of food residue

Abstract

Biocide inactivation of Bacillus anthracis spores in the presence of food residues after a 10-min treatment time was investigated. Spores of nonvirulent Bacillus anthracis strains 7702, ANR-1, and 9131 were mixed with water, flour paste, whole milk, or egg yolk emulsion and dried onto stainless-steel carriers. The carriers were exposed to various concentrations of peroxyacetic acid, sodium hypochlorite (NaOCl), or hydrogen peroxide (H(2)O(2)) for 10 min at 10, 20, or 30 degrees C, after which time the survivors were quantified. The relationship between peroxyacetic acid concentration, H(2)O(2) concentration, and spore inactivation followed a sigmoid curve that was accurately described using a four-parameter logistic model. At 20 degrees C, the minimum concentrations of peroxyacetic acid, H(2)O(2), and NaOCl (as total available chlorine) predicted to inactivate 6 log(10) CFU of B. anthracis spores with no food residue present were 1.05, 23.0, and 0.78%, respectively. At 10 degrees C, sodium hypochlorite at 5% total available chlorine did not inactivate more than 4 log(10) CFU. The presence of the food residues had only a minimal effect on peroxyacetic acid and H(2)O(2) sporicidal efficacy, but the efficacy of sodium hypochlorite was markedly inhibited by whole-milk and egg yolk residues. Sodium hypochlorite at 5% total available chlorine provided no greater than a 2-log(10) CFU reduction when spores were in the presence of egg yolk residue. This research provides new information regarding the usefulness of peroxygen biocides for B. anthracis spore inactivation when food residue is present. This work also provides guidance for adjusting decontamination procedures for food-soiled and cold surfaces.

FIG. 1.

Inactivation of Bacillus anthracis spores with peroxyacetic acid. Strains 7702, ANR-1, and 9131 were suspended in water, 10% flour paste, whole milk, and 50% egg yolk emulsion. Suspensions were dried onto stainless-steel coupons for 1 h and then exposed to peroxyacetic acid solutions for 10 min.

FIG. 2.

Inactivation of Bacillus anthracis spores with sodium hypochlorite. Strains 7702, ANR-1, and 9131 were suspended in water, 10% flour paste, whole milk, and 50% egg yolk emulsion. Suspensions were dried onto stainless-steel coupons for 1 h and then exposed to sodium hypochlorite solutions for 10 min. Total available chlorine levels also represented free available chlorine levels.

FIG. 3.

Inactivation of Bacillus anthracis spores with hydrogen peroxide. Strains 7702, ANR-1, and 9131 were suspended in water, 10% flour paste, whole milk, and 50% egg yolk emulsion. Suspensions were dried onto stainless-steel coupons for 1 h and then exposed to hydrogen peroxide solutions for 10 min.