title: Staphylococcus aureus dry-surface biofilms are not killed by sodium hypochlorite: implications for infection control.
abstract: BACKGROUND
  Dry hospital environments are contaminated with pathogenic bacteria in biofilms, which suggests that current cleaning practices and disinfectants are failing.
  
  
  OBJECTIVE
  To test the efficacy of sodium hypochlorite solution against Staphylococcus aureus dry-surface biofilms.
  
  
  METHODS
  The Centers for Disease Control and Prevention Biofilm Reactor was adapted to create a dry-surface biofilm, containing 1.36 × 10(7)S. aureus/coupon, by alternating cycles of growth and dehydration over 12 days. Biofilm was detected qualitatively using live/dead stain confocal laser scanning microscopy (CLSM), and quantitatively with sonicated viable plate counts and crystal violet assay. Sodium hypochlorite (1000-20,000parts per million) was applied to the dry-surface biofilm for 10min, coupons were rinsed three times, and residual biofilm viability was determined by CLSM, plate counts and prolonged culture up to 16 days. Isolates before and after exposure underwent minimum inhibitory concentration (MIC) and minimum eradication concentration (MEC) testing, and one pair underwent whole-genome sequencing.
  
  
  RESULTS
  Hypochlorite exposure reduced plate counts by a factor of 7 log10, and reduced biofilm biomass by a factor of 100; however, staining of residual biofilm showed that live S. aureus cells remained. On prolonged incubation, S. aureus regrew and formed biofilms. Post-exposure S. aureus isolates had MICs and MECs that were not significantly different from the parent strains. Whole-genome sequencing of one pre- and post-exposure pair found that they were virtually identical.
  
  
  CONCLUSIONS
  Hypochlorite exposure led to a 7-log kill but the organisms regrew. No resistance mutations occurred, implying that hypochlorite resistance is an intrinsic property of S. aureus biofilms. The clinical significance of this warrants further study.
authors.affiliation: Surgical Infection Research Group, Faculty of Medicine and Health Sciences, Macquarie University, New South Wales, Australia; Department of Medical Laboratories, College of Applied Medical Sciences, Qassim University, Qassim, Saudi Arabia.
authors.forename: A
authors.initials: A
authors.lastname: Almatroudi
authors.affiliation: Antibiotic Resistance and Mobile Elements Group, Ingham Institute for Applied Medical Research, Liverpool, New South Wales, Australia; Molecular Medicine Research Group, School of Medicine, Western Sydney University, New South Wales, Australia; Department of Microbiology & Infectious Diseases, Sydney South West Pathology Service - Liverpool, New South Wales Health Pathology, New South Wales, Australia.
authors.forename: I B
authors.initials: IB
authors.lastname: Gosbell
authors.affiliation: Surgical Infection Research Group, Faculty of Medicine and Health Sciences, Macquarie University, New South Wales, Australia.
authors.forename: H
authors.initials: H
authors.lastname: Hu
authors.affiliation: Antibiotic Resistance and Mobile Elements Group, Ingham Institute for Applied Medical Research, Liverpool, New South Wales, Australia; Molecular Medicine Research Group, School of Medicine, Western Sydney University, New South Wales, Australia.
authors.forename: S O
authors.initials: SO
authors.lastname: Jensen
authors.affiliation: Antibiotic Resistance and Mobile Elements Group, Ingham Institute for Applied Medical Research, Liverpool, New South Wales, Australia; Molecular Medicine Research Group, School of Medicine, Western Sydney University, New South Wales, Australia.
authors.forename: B A
authors.initials: BA
authors.lastname: Espedido
authors.affiliation: Surgical Infection Research Group, Faculty of Medicine and Health Sciences, Macquarie University, New South Wales, Australia.
authors.forename: S
authors.initials: S
authors.lastname: Tahir
authors.affiliation: Whiteley Corporation, North Sydney, New South Wales, Australia.
authors.forename: T O
authors.initials: TO
authors.lastname: Glasbey
authors.affiliation: Surgical Infection Research Group, Faculty of Medicine and Health Sciences, Macquarie University, New South Wales, Australia.
authors.forename: P
authors.initials: P
authors.lastname: Legge
authors.affiliation: Whiteley Corporation, North Sydney, New South Wales, Australia.
authors.forename: G
authors.initials: G
authors.lastname: Whiteley
authors.affiliation: Surgical Infection Research Group, Faculty of Medicine and Health Sciences, Macquarie University, New South Wales, Australia.
authors.forename: A
authors.initials: A
authors.lastname: Deva
authors.affiliation: Surgical Infection Research Group, Faculty of Medicine and Health Sciences, Macquarie University, New South Wales, Australia. Electronic address: Karen.vickery@mq.edu.au.
authors.forename: K
authors.initials: K
authors.lastname: Vickery
mesh_terms: D018441:Biofilms / Q000187:drug effects*; D015169:Colony Count, Microbial; D003681:Dehydration; D004202:Disinfectants / Q000494:pharmacology*; D004783:Environmental Microbiology; D017053:Infection Control / Q000379:methods; D008826:Microbial Sensitivity Tests; D050296:Microbial Viability / Q000187:drug effects*; D018613:Microscopy, Confocal; D012973:Sodium Hypochlorite / Q000494:pharmacology*; D013211:Staphylococcus aureus / Q000187:drug effects* / Q000502:physiology*; D013499:Surface Properties
chemical_list: D004202:Disinfectants; D012973:Sodium Hypochlorite
keywords: Biofilms; Disinfectants; Dry-surface biofilms; Healthcare-associated infections; Hospital cleaning; Infection control; Sodium hypochlorite; Staphylococcus aureus