P ROTE IN DE TECT ION
the limitations of current decontamination technologies and the design of some surgical instruments.20
Dense packing of instruments
in trays may contribute to masking some surfaces and limit the washing action of AWDs, while allowing transfer of soil to adjacent surfaces. We also compared known amounts of a common test soil (Browne) with real tissues placed on identical stainless steel surfaces and subjected to the same cycle, in two different models of AWDs. Variations between models were evident (the newest model performing better), but importantly we measured how easily Browne soil on a flat surface was removed compared to real tissue.
Interestingly the same Browne soil was harder to remove when partly masked, and it is encouraging to see some commercialised test stripes for washer disinfectors designed to present a more realistic challenge, rather than producing a comfortably reassuring 100% success.
A key benefit of EDIC/EF is that the effective (visible) range extends down to the picograms region. With such sensitivity it is hardly surprising we found protein residues on most instruments. In HTM 01-01 the recommended target has been set to 5µg per instrument side. Considering the limitations of swabbing tests which claim a sensitivity
in the microgram range (if that much is desorbed from the surface), setting the acceptable threshold at 10 µg of proteins still adsorbed on the surface of one instrument appears achievable with current processes. This way, the improvement in quality control while preserving existing protocols and equipment does not impact drastically on the provision of healthcare.
Since the inception of routine in situ protein detection, following the publication of HTM 01-01, SSD staff at Southampton have been regularly trained in using the EDIC/EF system. While most people nowadays are computer-literate, using a large and delicate research microscope requires a little bit more hand-on experience. Nevertheless, all trained staff have rapidly become confident and now use the device routinely.
Total protein detection is achieved using a non-toxic dye (SYPRO Ruby) which binds to protein residues within minutes, but not to the instrument surfaces. Once rinsed with deionised water and dried, the instruments are placed on the microscope stage. There each tested instrument can be first examined quickly without magnification thanks to the orange fluorescence produced by the dye under the appropriate light, observed through an appropriate filter attached in front of the stage (see Figure 1).
If proteinaceous residues are present, these can be observed closer and photographed for later reference (Figure 2). The images are analysed, and proteinaceous residues quantified from a pre-established calibration using a standard of choice. Several months or daily surveillance produced a significant amount of data and we could establish a hierarchy of instruments which consistently retained residual contamination.20
This can be useful when
selecting the most relevant instruments for routine surveillance, as it is impossible to check every single instrument.
Figure 1: The EDIC/EF system in place.
Conclusion Routine protein detection is well accepted as a quality control measure in SSDs. Technologies to perform more precise protein quantification on surfaces can provide
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