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Title: Understanding microbial survival in, and the development of resistance to, high-level disinfection
Author: Martin, Deborah J. H. Martin
ISNI:       0000 0004 2714 8849
Awarding Body: Cardiff University
Current Institution: Cardiff University
Date of Award: 2009
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High-level disinfection is employed throughout the health services in the disinfection of medical equipment, such as endoscopes, to prevent patient-to-patient infections. The likelihood of an endoscope transmitted infection occurring is rare, providing strict guidelines are followed for effective decontamination between procedures. Endoscopes are subjected to rigorous cleaning and high-level disinfection within washer-disinfectors. However, poor decontamination protocols and inappropriate use of disinfectants can lead to can lead to incomplete disinfection and resistance. A number of bacterial strains were isolated from endoscope washer-disinfectors on several occasions. The efficacy of high-level disinfectants (chlorine dioxide, peracetic acid and hydrogen peroxide-based) against these isolates was measured using standard efficacy tests. Resistance mechanisms involved in bacterial survival following biocide exposure were investigated using scanning and transmission electron-microscopy for gross-morphology changes, measurements of expression of detoxifying enzyme and RT-PCR for resistance genes expression, while the role of extracellular polysaccharide in decreasing biocide efficacy, was studied. Two bacterial isolates (Bacillus subtilis and Micrococcus luteus) were shown to have a high resistance to chlorine dioxide. Electron microscopy showed significant differences between isolates and reference strains. The B. subtilis isolate produced large quantities of extracellular polysaccharide, which may be interfering with biocide activity. Genes for catalase and superoxide dismutase were present in B. subtilis and enzyme activity varied between isolates and reference strains, indicating a potential involvement in resistance mechanisms, however the extent remains unclear. It was found that the isolate extracellular polysaccharide was not involved in conferring resistance to oxidising agents. This study demonstrated that bacteria can survive high-level disinfection with oxidising agents and that mechanisms conferring resistance are complex but might not be linked to impaired biocide penetration. Furthermore, the findings of this work show that surveillance programmes are essential for monitoring the incidence of biocide resistant isolates in the healthcare environment.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available