Efficacy of Disinfectants in Killing Spores of Alicyclobacillus acidoterrestris and Performance of Media for Supporting Colony Development by Survivors

Abstract

Alicyclobacillus has recently emerged as a spoilage microorganism of concern in a wide range of pasteurized fruit products. The focus of this study was to determine the efficacy of chemical disinfectants in killing Alicyclobacillus acidoterrestris spores. Direct plating media were evaluated for their suitability to support germination and outgrowth of spores surviving exposure to these disinfectants. Significant (P ≤ 0.05) reductions of about 2.2, 0.4, and 0.1 logs in the number of viable A. acidoterrestris spores in a five-strain mixture were achieved when spores were suspended in 200 ppm chlorine, 500 ppm acidified sodium chlorite, or 0.2% H2O2 solutions, respectively, for 10 min at 23°C. When treated with either 1,000 ppm chlorine or 4% H2O2, the number of spores was reduced by more than 5 logs. Treatment with 8% trisodium phosphate or 80 ppm Tsunami did not significantly reduce numbers of viable spores. Spores of individual strains of A. acidoterrestris varied little in resistance to the same chemical treatment. K agar (pH 3.7) was judged best for recovering chemically treated spores, compared to orange serum agar (pH 5.0) and potato dextrose agar (pH 3.5). Experiments were done to determine the effectiveness of chemical treatments in killing a mixed-strain inoculum of A. acidoterrestris spores on the surface of apples. Treatment with 500 ppm chlorine or 1,200 ppm acidified sodium chlorite for 1 min significantly (P ≤ 0.05) reduced the number of viable spores, but reductions were less than 1 log. Hydrogen peroxide (2%) was ineffective in killing spores remaining on the apple skin after treatment.