Inactivation of Bacillus cereus Attached to and in Biofilm on a Stainless Steel Surface by Combined Treatment of Gaseous Chlorine Dioxide and Heat

Introduction: Cross-contamination of foodborne pathogens is one of the most common causes of foodborne illnesses.  To prevent the cross-contamination, foodborne pathogens should be effectively decontaminated from food-contact surface and the sanitizers used should not be remained on the surface.

Purpose: This study was done to evaluate the lethal activity of gaseous ClO₂ and its synergistic lethal effect with heat treatment against B. cereus cells attached and in biofilm on stainless steel surface.

Methods: Spores of B. cereus were prepared and attached on stainless steel coupons (SSCs).  Biofilm of B. cereus was formed on SSCs in tryptic soy broth at 22°C for 24h followed by exposing to atmosphere with 100 % relative humidity at 22°C for 4 days to induce the sporulation.  SSCs containing B. cereus (attached spores or cells in biofilm) were incubated with gaseous ClO₂ (115-120 μg/ml) in an airtight container at 25°C or 55°C for up to 6h and the numbers of viable cells of B. cereus on SSCs were measured.

Results: When treated with gaseous ClO₂, B. cereus spore (5.3 log CFU/coupon) attached to SSC was completely inactivated within 1h and 30 min at 25°C and 55°C, respectively.  B. cereus (5.9 log CFU/coupon) in biofilm on SSCs was completely inactivated within 6h regardless of storage temperature after exposed to gaseous ClO₂.

Significance: We confirmed that ClO₂ gas was effective in killing B. cereus spores attached to or cells in biofilm on SSCs.  The synergistic lethal effect between ClO₂ gas and heat treatments was also observed.