Chlorine, chlorine dioxide kill spores on apples.

With increased attention focused on the threat of bioterrorism, produce and other ready-to-eat foods may be potential vehicles for intentional contamination with disease-causing microorganisms. While chlorine, chlorine dioxide and other sanitizers are effective in killing B. anthracis and other bioterrorism agents on inert surfaces and in aqueous suspensions, the resistance of B. anthracis spores and spores of other Bacillus species to sanitizers has been given less attention by researchers.

B. cereus and B. thuringiensis are genetically closely related to B. anthracis. Researchers at the University of Georgia undertook a study using B. cereus and B. thuringiensis spores as surrogates for B. anthracis. The goal was to evaluate the efficacy of chlorine and chlorine dioxide and a peroxyacetic acid-based sanitizer in killing spores of B. cereus and B. thuringiensis in suspension, on the surface of stainless steel and on apples as a ready-to eat model. Their insight will be useful when developing sanitization strategies associated with the Bacillus species.

The scientists used water and 5% horse serum as carriers for spore inoculum applied to the surface of stainless steel. A 5% horse serum was used as a carrier for inoculum applied to apples. Inocula were dried on stainless steel for 5 hours and on apples for up to 24 hours before they were treated with sanitizers. At certain concentrations, the sensitivity of planktonic B. cereus and B. thuringiensis spores to chlorine and chlorine dioxide was similar. A portion of the spores surviving treatment with chlorine and, more markedly, chlorine dioxide, had less tolerance to heat.

Treatment with the peroxyacetic acid-based sanitizer had little effect on the viability of spores. Planktonic spores of both species were more sensitive to chlorine and chlorine dioxide than were spores on the surface of stainless steel or apples. Chlorine was more effective than chlorine dioxide in killing spores in suspension and on stainless steel. The lethality of chlorine dioxide was markedly reduced when inoculum on stainless steel was suspended in 5% horse serum as a carrier rather than in water. This indicates that neutralization of the sanitizer occurred when it contacted the organic material.

Chlorine and chlorine dioxide were equally effective in killing spores on apples. Significant reductions of 3.8 to 4.5 log CFU per apple were achieved by a treatment concentration of 100 g per mL. Treatment with the peroxyacetic acid sanitizer caused reductions of Bacillus spores on the order of 1 log CFU per apple. Further information. Michael Doyle, Center for Food Safety, University of Georgia, Griffin Campus, Melton Building, Griffin, GA 30223; phone: [phone]; fax: [phone]; email: [e-mail].