Chemical Decontamination of Footwear Soles to Limit Microbial Transfer in a Dry Environment

Introduction: Safety of foods is often dependent on Good Manufacturing Practices (GMPs) including maintenance of manufacturing environments that prevent contamination of in-process or finished product materials. Decontamination of footwear soles by chemical sanitizers is often used to control the ingress and spread of pathogenic microorganisms over floor surfaces, although little has been published to validate effectiveness.

Purpose: This study evaluated four decontamination treatments for efficacy in reducing microbial populations on footwear soles and for reducing transfer from soles to floors.

Methods: Footwear soles were inoculated with an equal-part mixture of Citrobacter freundii, Pseudomonas fluorescens, and Serratia marcescens, donned, and subjected to treatment with aqueous quaternary ammonium sanitizer (Aqueous QAC, 1,000 ppm) in a footbath, dry quaternary ammonium sanitizer (Dry QAC, 1.2% (wt/wt)) in a footbath, 58.6% isopropyl alcohol solution containing 200 ppm quaternary ammonium compounds (IPA QAC) sprayed onto footwear soles and an IPA QAC spray followed by Dry QAC in a footbath (IPA QAC/Dry QAC). Before and after treatment, footwear soles and floor surfaces were sampled to determine microbial levels. Means of recovered populations based on results of three replicate experiments were calculated and compared using ANOVA.

Results: No significant differences (P > 0.05) in populations on soles were observed upon treatment with Aqueous QAC, Dry QAC, and no treatment (control). Decontamination with IPA QAC and IPA QAC/Dry QAC resulted in significant (P < 0.05) 2.3 and 3.5-log reductions, respectively. Populations recovered from floor surfaces after IPA QAC and IPA QAC/Dry QAC (2.14 and 1.98 log CFU, respectively) were significantly lower (P < 0.05) than those recovered prior to treatment (3.11 mean log CFU), whereas transfer was not impeded by Aqueous QAC or Dry QAC alone.

Significance: Results of this study demonstrate that use of IPA QAC in the decontamination of footwear may provide an effective barrier against the spread of microorganisms by foot traffic. Furthemore, use of IPA QAC spray may be more effective than Aqueous QAC, 1,000 ppm in a footbath for decontamination of footwear, while helping to reduce presence of water in manufacturing plant environments.