title: The antimicrobial effects of helium and helium-air plasma on Staphylococcus aureus and Clostridium difficile.
abstract: Healthcare-associated infections (HCAI) affect 5-10% of acute hospital admissions. Environmental decontamination is an important component of all strategies to prevent HCAI as many bacterial causes survive and persist in the environment, which serve as ongoing reservoirs of infection. Current approaches such as cleaning with detergents and the use of chemical disinfectant are suboptimal. We assessed the efficacy of helium and helium-air plasma in killing Staphylococcus aureus and Clostridium difficile on a glass surface and studied the impact on bacterial cells using atomic force microscopy (AFM). Both plasma types exhibited bactericidal effects on Staph. aureus (log3·6 - >log7), with increased activity against methicillin-resistant strains, but had a negligible effect on Cl. difficile spores (<1log). AFM demonstrated cell surface disruption. The addition of air increased the microbicidal activity of the plasma and decreased the exposure time required for an equivalent log reduction. Further evaluation of cold plasma systems is warranted with, for example, different bacteria and on surfaces more reminiscent of the health care environment as this approach has potential as an effective decontaminant.
  
  
  CONCLUSIONS
  Many bacterial causes of healthcare infection can survive in the inanimate environment for lengthy periods and be transmitted to patients. Furthermore, current methods of environmental decontamination such as detergents, chemical disinfectants or gaseous fumigation are suboptimal for a variety of reasons. We assessed the efficacy of helium and helium-air plasma as a decontaminant and demonstrated a significant reduction in bacterial counts of Staphylococcus aureus on a glass surface. Atomic force microscopy morphologically confirmed the impact on bacterial cells. This approach warrants further study as an alternative to current options for hospital hygiene.
authors.affiliation: Department of Clinical Microbiology, Education and Research Centre, Royal College of Surgeons in Ireland, Dublin, Ireland.
authors.forename: S
authors.initials: S
authors.lastname: Galvin
authors.forename: O
authors.initials: O
authors.lastname: Cahill
authors.forename: N
authors.initials: N
authors.lastname: O'Connor
authors.forename: A A
authors.initials: AA
authors.lastname: Cafolla
authors.forename: S
authors.initials: S
authors.lastname: Daniels
authors.forename: H
authors.initials: H
authors.lastname: Humphreys
mesh_terms: D000388:Air; D058491:Bacterial Load; D016360:Clostridioides difficile / Q000187:drug effects* / Q000502:physiology / Q000648:ultrastructure; D003666:Decontamination / Q000379:methods; D004202:Disinfectants / Q000494:pharmacology; D005898:Glass; D006371:Helium / Q000494:pharmacology*; D055624:Methicillin-Resistant Staphylococcus aureus / Q000187:drug effects* / Q000502:physiology / Q000648:ultrastructure; D050296:Microbial Viability; D018625:Microscopy, Atomic Force; D058626:Plasma Gases / Q000494:pharmacology*; D013171:Spores, Bacterial / Q000187:drug effects; D013211:Staphylococcus aureus / Q000187:drug effects* / Q000502:physiology / Q000648:ultrastructure
chemical_list: D004202:Disinfectants; D058626:Plasma Gases; D006371:Helium
keywords: biocides; disinfection; environmental; microbial contamination