Electro-elution – a novel TSE decontamination technique for surgical instruments

Chris Plinston
BSc
Research Scientist
Neuropathogenesis Unit
Roslin Insitute

The transmissible spongiform encephalopathies (TSEs) such as Creutzfeldt–Jakob disease (CJD) and its variant form (vCJD) in humans, bovine spongiform encephalopathy (BSE) in cattle and scrapie in sheep are invariably fatal neurodegenerative diseases of the central nervous system.
The high resistance of TSE agents to conventional methods of chemical or thermal inactivation(1) and to UV or ionising radiation, as well as their high binding affinity to steel surfaces,(2) warrants specific decontamination procedures in the reprocessing of surgical instruments. Current washer-disinfectors employed by hospital sterilisation departments are inadequate to cope with TSE-contaminated surgical instruments. 

The disposal or quarantine of all instruments used on known or suspect patients, and for high-risk patients when contact is made with high-risk tissue, is recommended.(3)  However, we cannot rely on the disposal or quarantine of instruments as concern cannot be restricted to just high-risk tissue since infectivity has been detected ante mortem in the appendix and tonsils of cases of vCJD,(4,5) and we now know that infectivity can be present in the blood of cases of vCJD for many years before the onset of clinical signs.(6,7) This raises the concern that all surgical procedures may be at risk. Single-use surgical instruments could be employed for all surgical procedures and would effectively remove the threat of accidental transmission. However, the implementation of such a strategy would have significant financial implications, and would ultimately be prohibitive.

To combat these issues we have developed the novel decontamination process known as electro-elution(8) that utilises an electrical current through an electrolytic buffer to effectively remove, and possibly degrade, TSE disease-associated PrPsc contamination from the surface of stainless steel. 

Prototype electro-elution tanks
Two prototype electro-elution tanks were developed. The first (CP1) was constructed using an XCell II electrophoresis tank (Invitrogen, UK) and tested the general effectiveness of the electro-elution process. The second (CP2) was constructed using a 40 ml polypropylene sample container and tested the electrolyte buffer for any residual contamination.

Electro-elution procedure
Murine-passaged scrapie (ME7) brain homogenate was prepared and applied to the surface of a stainless-steel disc (EN420 surgical-grade stainless steel). The disc is attached to the cathode and submerged in electrolyte buffer pH 7.5 (sodium carbonate). The contaminated disc is then subjected to an electrical current. Upon completion the disc and electrolyte buffer are analysed for PrPsc using either direct blotting (presence of PrP on the surface of the disc) or western blotting (presence of PrP in the electrolyte buffer).(9)

Outcome
Initial studies have shown that PrPsc, a marker for TSE infectivity, can no longer be detected on the surface of surgical-grade stainless-steel discs following 5 min electro-elution at 12 V in 0.5% electrolyte buffer. Further investigation has shown that a reduction in electrolyte concentration (see Figure 1), or a reduction in exposure time (see Figure 2) have no adverse effects on the removal of the contamination. The apparent efficiency of the process will not only allow a quick turnover of instruments but is also relatively safe for the operator.

[[HHE07_fig1_T26]]

[[HHE07_fig2_T26]]

Next we had to determine what happens to the PrPsc following the electro-elution process. The main concern is that the infectious material will remain present in the electrolyte buffer following a decontamination cycle.  If the PrPsc is removed into the electrolyte buffer this could lead to recontamination of existing instruments, or the contamination of future instruments not necessarily contaminated with TSE material.

Our studies have found that following electro-elution there is no detectable PrPsc present in the electrolyte buffer (see Figure 3), which suggests the PrPsc molecule is undergoing some form of degradation. Further investigation is required to determine whether the electro-elution process does indeed destroy the infectious agent that causes the TSE disease.

[[HHE07_fig3_T26]]

Conclusion
Taking into account the stubborn nature of TSE material this relatively simple approach to the problem seems to have had quite unexpected results. These pilot studies suggest that electro-elution may be a simple, effective and economical procedure of removing TSE infectious deposits from the surfaces of stainless-steel surgical instruments. 

The simplicity of the electro-elution process means that it could be used in conjunction with current sterilisation techniques to recycle high-risk surgical instruments. Work is already underway to determine whether the process can be incorporated into existing washer-disinfectors employed by hospital sterilisation departments.

Acknowledgements
We would like to thank Karen Fernie (Neuropathogenesis Unit, Roslin Institute) and Frank Prior (Synergy Health Group) for their assistance in the invention and development of the electro-elution process.  We gratefully acknowledge that part of this research was funded by the Department of Health, UK.

References

1. Taylor DM. Inactivation of transmissible degenerative encephalopathy agents: a review. Vet J 2000;159(1):10-7.
2. Flechsig E, Hegyi I, Enari M, Schwarz P, Collinge J, Weissman C. Transmission of scrapie by steel surface bound prions. Mol Med 2001;7(10):679-84.
3. ACDP/SEAC. Transmissible spongiform encephalopathy agents: safe working and the prevention of infection. London, UK: The Stationery Office; 1998.
4. Ironside JW. Neuropathology of variant Creutzfeldt–Jakob disease. C R Biol 2002;325(1):27-31.
5. Ironside JW, McCardle L, Horsburgh A, Lim Z, Head MW. Pathological diagnosis of variant Creutzfeldt–Jakob disease. APMIS 2002; 110:(1):79-87. Review.
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8. Prior FGR. Apparatus and method for electrolytic cleaning. British Patent Application 2005. 0423817.6 and 0423339.1.
9. Plinston C, Fernie K, Prior F, Smith R. Electro-elution, a novel method to remove transmissible spongiform encephalopathy-associated PrPsc from stainless steel surgical instruments. J Hosp Infect 2007;66(1):52-8.