title: Bacillus subtilis vegetative isolate surviving chlorine dioxide exposure: an elusive mechanism of resistance.
abstract: OBJECTIVE
  Oxidizing agents such as chlorine dioxide are widely used microbicides, including for disinfection of medical equipment. We isolated a Bacillus subtilis isolate from a washer-disinfector whose vegetative form demonstrated unique resistance to chlorine dioxide (0·03%) and hydrogen peroxide (7·5%). The aim of this study was to understand the mechanisms of resistance expressed by this isolate.
  
  
  RESULTS
  A range of resistance mechanisms were investigated in the B. subtilis isolate and a reference B. subtilis strain (ATCC 6051) to include bacterial cell aggregation, the presence of profuse exopolysaccharide (EPS), and the expression of detoxification enzymes. The basis of resistance of the isolate to high concentrations of oxidizing agents was not linked to the presence of endospores. Although, the presence of EPS, aggregation and expression of detoxification enzymes may play a role in bacterial survival to low concentrations of chlorine dioxide, it is unlikely that the mechanisms helped tested to survive the bactericidal effect of higher oxidizer concentrations.
  
  
  CONCLUSIONS
  Overall, the mechanisms conferring resistance to chlorine dioxide and hydrogen peroxide remains elusive. Based on recent advances in the mode of action of oxidizing agents and notably hydrogen peroxide, we postulate that additional efficient intracellular mechanisms may be involved to explain significant resistance to in-use concentrations of commonly used high-level disinfectants.
  
  
  CONCLUSIONS
  The isolation of a highly resistant vegetative Gram-positive bacterium to a highly reactive oxidizing agent is worrying. Understanding the mechanisms conferring such resistance is essential to effectively control such bacterial isolates. Here, we postulate that there are still mechanisms of bacterial resistance that have not been fully characterized.
authors.affiliation: Cardiff School of Pharmacy and Pharmaceutical Sciences, Cardiff University, Cardiff, UK.
authors.forename: D J H
authors.initials: DJ
authors.lastname: Martin
authors.affiliation: Cardiff School of Pharmacy and Pharmaceutical Sciences, Cardiff University, Cardiff, UK.
authors.forename: R L
authors.initials: RL
authors.lastname: Wesgate
authors.affiliation: Cardiff School of Pharmacy and Pharmaceutical Sciences, Cardiff University, Cardiff, UK.
authors.forename: S P
authors.initials: SP
authors.lastname: Denyer
authors.affiliation: STERIS Corp., Mentor, OH, USA.
authors.forename: G
authors.initials: G
authors.lastname: McDonnell
authors.affiliation: Cardiff School of Pharmacy and Pharmaceutical Sciences, Cardiff University, Cardiff, UK.
authors.forename: J-Y
authors.initials: JY
authors.lastname: Maillard
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D001412:Bacillus subtilis / Q000187:drug effects* / Q000302:isolation & purification*; D017606:Chlorine Compounds / Q000494:pharmacology*; D024881:Drug Resistance, Bacterial; D016877:Oxidants / Q000494:pharmacology*; D010087:Oxides / Q000494:pharmacology*
chemical_list: D000900:Anti-Bacterial Agents; D017606:Chlorine Compounds; D016877:Oxidants; D010087:Oxides; C025109:chlorine dioxide
keywords: Bacillus subtilis; chlorine dioxide; exopolysaccharide; high-level resistance; oxidizing agents