Transcriptional Profile of Listeria monocytogenes Exposed to Sublethal Chlorine Dioxide

Introduction:  There is increasing interest in the use of chlorine dioxide (ClO₂) as a sanitizer in food systems. ClO₂ is a strong oxidizing sanitizer that effectively decreases contamination of foodborne microorganisms on the surfaces of foods and food processing equipment.  To date, little is known how ClO₂ inactivates microorganisms and the microbial stress response mechanisms foodborne pathogens employ to survive this sanitizer.

Purpose:  The purpose of this study was to identify genes differentially expressed in Listeria monocytogenes exposed to sublethal ClO₂ concentrations to gain insight into stress response mechanisms that may be used to survive ClO₂ exposure.

Methods:  L. monocytogenes 10403S was grown to early log phase (OD₆₀₀ = 0.4) in Brain Heart Infusion (BHI) broth and exposed to 300 mg/l of aqueous ClO₂ at 37°C, 230 rpm.   RNA was extracted following exposure to ClO₂; gene expression levels from untreated and treated cells were compared on 70-mer L. monocytogenes microarrays.  Expression fold changes ≥ 1.5 with a corresponding adjusted P-value of <0.05 were considered significantly differentially expressed.  RNA extractions and microarrays were completed in quadruplicate. 

Results:  Cells treated with 300 mg/l aqueous ClO₂ for 15 minutes resulted in a 0.58 + 0.24 log CFU/ml reduction of L. monocytogenes.  Data analysis identified 238 up-regulated and 116 down-regulated genes in L. monocytogenes 10403S exposed to ClO₂.  Among the 238 up-regulated genes, 115 genes have been previously reported to be regulated by σB, a major stress response regulator. Five up-regulated genes encoding proteins with oxidoreductase activity were identified, which may significantly contribute to ClO₂stress survival.

Significance:  This is the first transcriptomic study, to our knowledge, to investigate stress response of L. monocytogenes to sublethal concentrations of ClO₂. Understanding potential survival mechanisms may provide significant insight into the specific mode of action of ClO₂ as a sanitizer.