Safety and cleaning of medical materials and devices

A study was undertaken to evaluate different procedures to safely remove microorganisms, protein, and mammalian cells from materials and provide a suitable method for cleaning and assessing effectiveness of cleaning medical devices for reuse or for analysis of failure. Safety considerations for the personnel performing the cleaning or handling the device after cleaning are important issues. Polystyrene plates (96 well) were used to simulate device surfaces not amenable to manual scrubbing. Staphylococcus epidermidis, Candida albicans, Escherichia coli, Pseudomonas aeruginosa, and oral flora were grown in the plates. The plates were stained with crystal violet and the optical densities recorded. The results indicated that E. coli did not adhere well and Pseudomonas formed clumps that were easily detached from the surface of the plates. However, S. epi, C. albicans, and the oral organisms formed adherent biofilms that were difficult to remove from the plates. Detergents with enzymes and sodium hypochlorite (NaOCl) bleach were both effective in removing the biofilm. Other detergents and surfactants were not effective. The aldehyde agents did not remove the organisms and made further cleaning difficult. Allowing the biofilm to dry first made cleaning very difficult. Only the NaOCl bleach could subsequently remove the dried or aldehyde fixed organisms from the wells. The same 96-well polystyrene plate format was used to measure the amount of protein and cell adherence as well as the effectiveness of subsequent cleaning. Bradford reagent was used to detect protein as a measure of the cleaning efficacy. As with the bacteria, NaOCl bleach was effective at removing the protein and cells that had been dried or fixed by formalin or alcohol, whereas detergent with enzymes was not very effective. This study confirmed that used medical devices, contaminated with microorganisms, protein, and/or mammalian cells, should not be allowed to dry before cleaning and that a thorough cleaning procedure should precede sterilization or disinfection (with the exception of NaOCl bleach which also cleans).