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Title: Assessing hygienic performance of stainless steel
Author: Airey, Paul
ISNI:       0000 0001 3403 3482
Awarding Body: Manchester Metropolitan University
Current Institution: Manchester Metropolitan University
Date of Award: 2008
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Viable bacteria on hard, open surfaces are usually present alongside some organic (or inorganic) material, typically at the solid-air interface. Even if not multiplying, the presence ofthese viable cells presents a risk to overall hygiene levels. Stainless steel is typically the material ofchoice as a hygienic surface, being hard, inert and easy to clean. Properties ofc1eanability in addition to ease of disinfection are key in the evaluation of hygienic surfaces. The aim of this study was to evaluate the hygienic status and cIeanability ofstainless steel surfaces under test conditions which more closely resemble the environment under investigation, by monitoring survival at the solid-air (rather than solid-liquid) interface, in the presence oforganic material. A range ofmethods were developed: - A synthetic fingerprint emulsion was developed by combining and modifYing published standard sweat and sebum formulations. The formulation allowed survival of large, but decreasing suspended populations ofStaphylococcus aureus and Esche'richia coli, for up to 48h, but on surfaces, no viable cells were recovered - in contrast to observations using real fingerprints. Thus the published formulation, which had been developed for physical/chemical testing, was not appropriate for combination with microorganisms, although was used to evaluate sUrface c1eanability. Results showed the importance of combining p!J,ysical and chemical cleaning strategies. - A 'hard-to-remove' surface soil Cburnt on' milk) was more effectively removed from the smoother oftwo stainless steel surfaces tested (bright annealed), particularly when cleaning parallel to, rather than across, linear surface features. - The requirement for moisture to release active agents from proposed antibacterial surfaces was demonstrated for a silver-containing polymer-coated stainless steel, by monitoring microbial survival at the solid-air interface for up to 3 weeks. Key parameters affecting hygienic status and cleanability were combined to assess the hygienic performance of stainless steel and copper, the latter of which had showed strong antibacterial activity when exposed to cells in nutrient broth. The test included repeated soiling and cleaning cycles, daily for 5 days, with a suspension ofSaureus in bovine serum albumen, inoculated onto three stainless steels of different surface finish, and copper. After the second and subsequent soiling, a layer of material readily stained with the fluorescent dye acridine orange, wasupparent on the copper surface, and any antibacterial effects were absent. Stainless steel, however, remained highly cleanable. A range of methods have been developed which enable the screening of proposed hygienic and/or antibacterial surfaces, combined with a variety ofcleaning and disinfection protocols, under challenging environinental conditions. All commercially available stainless steel finishes tested were comparable in terms of hygienic status (removal ofmicroorganisms), but even a small increase in surface topography (Ra = 20 to 100 nm) resulted in increased retention of organic soil. Thus cleanability remains a key step in ensuring maintenance of hygienic status, and an inert and highly cleanable surface provides the best option in this context.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available