Eradication of Salmonella in a Dry Processing Environment: First Step Moisten, Second Step Decontaminate

Introduction: Current thought is that for dry processing facilities it is best to keep the environment dry, making the environment un-inhabitable for microorganisms.  Microorganisms are harder to kill in dry environments, and as a result the options available to decontaminate dry processing areas are very limited. This creates a necessity for exploring other ways to eradicate microorganisms.  A new thought is to make the area humid and hospitable to microorganisms prior to decontamination in order to make the microorganisms easier to kill.

Purpose: A study was initiated to validate the efficacy of chlorine dioxide gas (CD) on the inactivation of Salmonella Typhimurium at low concentration levels and in short periods of time under dry environments.  Traditional exposure for CD to achieve a 6-log sporicidal kill is 720 ppm-hours.  As Salmonella Typhimurium is non-sporeforming, a much lower exposure level was studied to explore its effect on the bacterium. The long drying time study represents conditions more similar to the actual conditions of a dry processing environment, demonstrating that by keeping the area dry it is increasing the survival capabilities of Salmonella.  Fumigation using gaseous chlorine dioxide will eradicate all microorganisms to prevent the reoccurrence of persistent contaminations, and the first step for successful decontamination is to raise the humidity.

Methods: Testing was performed inside a 17 ft³ glove-box isolator with an automated CD generation system for optimal control over all factors being studied.  Glass coupons inoculated with Salmonella Typhimurium were introduced into the chamber and exposed to 50 – 720 ppm-hr decontamination cycles at 0.3 and 1 mg/l. Drying times before exposure were 2, 24, 72, and 96 hrs. The inoculated and exposed strips were then enumerated and/or enriched along with proper controls to determine the total log reduction.

Results:   Under the low-level exposure cycles, CD was able to achieve a 7-log reduction of Salmonella Typhimurium at 200 ppm-hrs after a 2-hr drying time.  A very important finding was that the longer the drying time was, the more difficult it was to achieve significant log reductions of Salmonella.  A case study where a 280,000 ft³ dry protein powder processing facility contaminated with Salmonella was decontaminated entirely at one time using chlorine dioxide gas under the findings of the study will also be discussed.  Pictures, explanations and data will be provided detailing the entire study.

Significance:   Many food processing environments are dry processing environments where there is a necessity for keeping the relative humidity very low (i.e., infant formula production, flour, protein powder, soy powder, etc.). This study shows that humidifying the environment prior to decontamination is an important step towards eliminating microorganisms.  The case study displays the real-life ability of chlorine dioxide gas to decontaminate large scale facilities, and how its use along with pre-humidification can eliminate a persistent Salmonella contamination.