Decontamination of surgical instruments from prion proteins: in vitro studies on the detachment, destabilization and degradation of PrPSc bound to steel surfaces

Kinetics of the reduction of Creutzfeldt-Jakob disease prion seeding activity by steam sterilization support the use of validated 134°C programmes

BACKGROUND

Prions are renowned for their distinct resistance to chemical or physical inactivation, including steam sterilization. Impaired efficacy of inactivation poses a risk to patients for iatrogenic transmission of Creutzfeldt-Jakob disease (CJD) via contaminated surgical instruments.

AIMS

Most established prion inactivation methods were validated against scrapie agents, although those were found to be generally less thermostable than human prions. Thus, knowledge gaps regarding steam-sterilization kinetics of CJD prions should be filled and current guidelines reviewed accordingly.

METHODS

Prion inactivation through widely recommended steam sterilization at 134°C was assessed for several holding times by analysing the residual prion seeding activity using protein misfolding cyclic amplification (PMCA).

FINDINGS

Scrapie 263K was found to be the least thermoresistant prion strain showing no seeding activity after 1.5 min at 134°C, while variant CJD was the most stable one demonstrating some seeding activity even after 18 min of steam sterilization. Sporadic CJD subtype VV2 exhibited residual seeding activity after 3 min, but no detectable activity after 5 min at 134°C.

CONCLUSION

Validated steam sterilization for 5 min at 134°C as previously recommended for the routine reprocessing of surgical instruments in contact with high-risk tissues is able to substantially reduce the seeding activity of CJD agents, provided that no fixating chemical disinfection has been performed prior to sterilization and that thorough cleaning has reduced the protein load on the surface to less than 100 μg per instrument.

Infection Control for Perioperative Ultrasonography and Echocardiography

Ultrasound technology has revolutionized point-of-care diagnostics, decision-making, and the guidance of interventional procedures in Anesthesiology and Perioperative Medicine. Recent literature has highlighted important infection control considerations when performing transesophageal or transthoracic echocardiography, point-of-care ultrasound, and ultrasound-guided procedures. This narrative review focuses on operator precautions and disinfection methods and summarizes key recommendations from the international Echocardiography and Radiology Societies.

A review of cleaning and disinfection guidelines and recommendations following an outbreak of classical scrapie

Classical scrapie is a prion disease of small ruminants, the infectious agent of which has been shown to be extremely persistent in the environment. Cleaning and disinfection (C&D) after a scrapie outbreak is currently recommended by many governments' veterinary advisors and implemented in most farms affected. Yet, the effectiveness of these procedures remains unclear. The aim of this study was to review existing literature and guidelines regarding farm C&D protocols following classical scrapie outbreaks and assess their effectiveness and the challenges that translation of policy and legislative requirements present at a practical level. A review of the literature was conducted to identify the on-farm C&D protocols used following outbreaks of scrapie, assess those materials with high risk for persistence of the scrapie agent on farms, and review the existing evidence of the effectiveness of recommended C&D protocols. An expert workshop was also organised in Great Britain (GB) to assess: the decision-making process used when implementing C&D protocols on GB farms, the experts' perceptions on the effectiveness of these protocols and changes needed, and their views on potential recommendations for policy and research. Outputs of the literature review revealed that the current recommended protocol for C&D [1 h treatment with sodium hypochlorite containing 20,000 ppm free chlorine or 2 M sodium hydroxide (NaOH)] is based on laboratory experiments. Only four field farm experiments have been conducted, indicating a lack of data on effectiveness of C&D protocols on farms by the re-occurrence of scrapie infection post re-stocking. Recommendations related to the control of outdoor environment, which are difficult and expensive to implement, vary between countries. The expert workshop concluded that there are no practical, cost-effective C&D alternatives to be considered at this time, with control therefore based on C&D only in combination with additional time restrictions on re-stocking and replacement with non-susceptible livestock or more genetically resistant types, where available. Participants agreed that C&D should still be completed on scrapie affected farms, as it is considered to be "good disease practice" and likely to reduce the levels of the prion protein. Participants felt that any additional protocols developed should not be "too prescriptive" (should not be written down in specific policies) because of significant variation in farm types, farm equipment and installations. Under this scenario, control of classical scrapie on farms should be designed with a level of C&D in combination with re-stocking temporal ban and replacement with livestock of limited susceptibility.

ATP Bioluminescence for Assessing the Efficacy of the Manual Cleaning Procedure during the Reprocessing of Reusable Surgical Instruments

Achieving sterilization by adopting proper practices is essential to ensure that surgical instruments do not transmit microorganisms to patients. As the effectiveness of sterilization mandates effective cleaning, it is necessary to verify the success of cleaning procedures. In this study, we used the adenosine triphosphate (ATP) bioluminescence method for assessing the efficacy of the manual cleaning procedure during the reprocessing of reusable surgical instruments. The ATP bioluminescence assay was performed on 140 surgical instruments of 12 different types, both before being cleaned (baseline) and after each of the cleaning procedures (i.e., decontamination, manual washing, drying, and visual inspection). For each instrument, two swabs were used as follows: one to sample the entire surface (test point 1) and the other to sample the most difficult part of the surface to clean (test point 2). Overall, for each type of instrument, there was a decrease in contamination ranging from 99.6 to >99.9% (log reduction from 2.40 to 3.76). Thus, in order to standardize the assessment of cleanliness, it may be useful to introduce the bioluminescence method into the daily routine or, at least, at regular time intervals as a complementary check combined with visual inspection. This would allow real-time verification of the achievement of an adequate level of cleanliness.

Improved surveillance of surgical instruments reprocessing following the variant Creutzfeldt-Jakob disease crisis in England: findings from a three-year survey

BACKGROUND

Sensitive, direct protein-detection methods are now recommended for the inspection of reprocessed reusable surgical instruments in England to reduce the risk of prion transmission.

AIM

To implement an established, highly sensitive method to quantify proteinaceous residues on reprocessed instruments in a Sterile Services Department (SSD) and evaluate its potential impact on service provision.

METHODS

We introduced highly sensitive epifluorescence (EDIC/EF) microscopy in a large SSD. Over three years, we periodically tested two models of washer disinfector using stainless-steel tokens spiked with mouse brain homogenate or Browne test soil for comparison. We also obtained data and feedback from staff who had been using EDIC/EF to examine almost 3000 reprocessed instruments.

FINDINGS

All reprocessed test surfaces harboured residual contamination (up to 258.4 ng from 1-μg spikes). Proximity between surfaces affected decontamination efficacy and allowed cross-contamination. Up to 50 ng de novo proteinaceous contamination was deposited on control surfaces after a single automated washer disinfector (AWD) cycle. The test soil behaved differently than real tissue contamination. SSD staff observed proteinaceous residues on most reprocessed instruments using EDIC/EF, which can detect far smaller amounts than the currently accepted national threshold of 5 μg per side.

CONCLUSIONS

Implementing recent national guidelines to address the prions concern proved an eye-opener. Microscopic levels of proteins remain on many reprocessed instruments. The impact most of these residues, potentially including prions, may have on subsequent patients after sterilization remains debatable. Improving surveillance capability in SSDs can support decision making and raise the standards of surgical instruments reprocessing.

Alpha-synuclein seeds of Parkinson's disease show high prion-exceeding resistance to steam sterilization

BACKGROUND

Cerebral deposition of abnormally misfolded and aggregated alpha-synuclein (αSyn) is a neuropathological hallmark of Parkinson's disease (PD). Pathologically aggregated αSyn species of PD (αSyn^PD) can act, in a 'prion-like' manner, as proteinaceous nuclei ('seeds') which are capable of self-templated propagation. This has raised concerns that αSyn^PD seeds transmitted iatrogenically between humans may stimulate αSyn pathologies or clinically harmful effects in the recipients. Effective decontamination when reprocessing medical devices could significantly counteract such risks. Steam sterilization at 134°C is recommended as an essential pathogen inactivation step in many reprocessing guidelines for medical devices, and also shows effectiveness against prions, the self-propagating biological agents long thought to exhibit the highest resistance to steam sterilization.

METHODS

This study examined the reduction in αSyn^PD seeding activity in brain tissue homogenates from patients with PD after steam sterilization at 134°C using a specifically adapted real-time quaking induced conversion assay.

FINDINGS

Titres of approximately 10¹⁰ 50% seeding doses per gram were detected in non-steam-sterilized caudate nucleus tissue of patients with PD by endpoint titration. Five minutes of steam sterilization reduced this titre by only 2.25 ± 0.15 decadic-logarithmic units, with an extension of the sterilization time to 90 min not causing additional inactivation. These findings reveal that αSyn^PD species are disease-associated biological agents with seeding activity that has higher resistance to steam sterilization than prions.

CONCLUSION

The remarkable heat resistance of αSyn^PD seeds calls for thoroughly validated cleaning and disinfection methods that reliably remove or inactivate possible contaminations of seeding-active αSyn aggregates when reprocessing medical devices.

Strain variation in treatment and prevention of human prion diseases

Transmissible spongiform encephalopathies or prion diseases describe a number of different human disorders that differ in their clinical phenotypes, which are nonetheless united by their transmissible nature and common pathology. Clinical variation in the absence of a conventional infectious agent is believed to be encoded by different conformations of the misfolded prion protein. This misfolded protein is the target of methods designed to prevent disease transmission in a surgical setting and reduction of the misfolded seed or preventing its continued propagation have been the focus of therapeutic strategies. It is therefore possible that strain variation may influence the efficacy of prevention and treatment approaches. Historically, an understanding of prion disease transmission and pathogenesis has been focused on research tools developed using agriculturally relevant strains of prion disease. However, an increased understanding of the molecular biology of human prion disorders has highlighted differences not only between different forms of the disease affecting humans and animals but also within diseases such as Creutzfeldt-Jakob Disease (CJD), which is represented by several sporadic CJD specific conformations and an additional conformation associated with variant CJD. In this chapter we will discuss whether prion strain variation can affect the efficacy of methods used to decontaminate prions and whether strain variation in pre-clinical models of prion disease can be used to identify therapeutic strategies that have the best possible chance of success in the clinic.

Transcriptomic Adjustments of Staphylococcus aureus COL (MRSA) Forming Biofilms Under Acidic and Alkaline Conditions

Methicillin-resistant Staphylococcus aureus (MRSA) strains are important human pathogens and a significant health hazard for hospitals and the food industry. They are resistant to β-lactam antibiotics including methicillin and extremely difficult to treat. In this study, we show that the Staphylococcus aureus COL (MRSA) strain, with a known complete genome, can easily survive and grow under acidic and alkaline conditions (pH5 and pH9, respectively), both planktonically and as a biofilm. A microarray-based analysis of both planktonic and biofilm cells was performed under acidic and alkaline conditions showing that several genes are up- or down-regulated under different environmental conditions and growth modes. These genes were coding for transcription regulators, ion transporters, cell wall biosynthetic enzymes, autolytic enzymes, adhesion proteins and antibiotic resistance factors, most of which are associated with biofilm formation. These results will facilitate a better understanding of the physiological adjustments occurring in biofilm-associated S. aureus COL cells growing in acidic or alkaline environments, which will enable the development of new efficient treatment or disinfection strategies.

Prion disease and recommended procedures for flexible endoscope reprocessing - a review of policies worldwide and proposal for a simplified approach

Several guidelines recommend specific treatments for endoscopes, procedures of quarantine for endoscopes, or additional treatments for the endoscope washer disinfector (EWD) in suspected or confirmed cases of Creutzfeldt-Jakob disease (CJD) or variant CJD (vCJD) but vary in many details. This study therefore reviewed guidelines on reprocessing flexible endoscopes after use in patients with suspected or confirmed prion disease. In addition, a literature search was performed in Medline on prion, CJD, vCJD, chemical inactivation, transmission healthcare, epidemiology healthcare, concentration tissue human and endoscope. Thus far, no case of CJD or vCJD transmitted by flexible endoscope has been reported. In animals it has been shown that oral uptake of 0.1-5 g of bovine spongiform encephalopathy (BSE)-infected brain homogenate is necessary for transmission. The maximum prion concentration in other tissues (e.g., terminal ileum) is at least 100-fold lower. Automated cleaning of endoscopes alone results in very low total residual protein ≤5.6 mg per duodenoscopes. Recommendations vary between countries, sometimes with additional cleaning, use of alkaline cleaners, no use of cleaners with fixative properties, use of disinfectants without fixative properties or single-use disinfectants. Sodium hydroxide (1 M) and sodium hypochlorite (10,000 and 25,000 mg/L) are very effective in preventing transmission via contaminated wires implanted into animal brains, but their relevance for endoscopes is questionable. Based on circumstantial evidence, it is proposed to consider validated reprocessing as appropriate in the case of delayed suspected prion disease when immediate bedside cleaning, routine use of alkaline cleaners, no fixative agents anywhere prior to disinfection and single use brushes and cleaning solutions can be assured.

Optimization of the photodynamic inactivation of prions by a phthalocyanine photosensitizer: The crucial involvement of singlet oxygen

Prion disorders are fatal neurodegenerative diseases caused by the autocatalytic conversion of a natively occurring prion protein (PrP^C ) into its misfolded infectious form (PrP^TSE ). The proven resistance of PrP^TSE to common disinfection procedures increases the risk of prion transmission in medical settings. Herein, we present the effective photodynamic inactivation (PDI) of prions by disulfonated hydroxyaluminum phthalocyanine (AlPcOH(SO₃ )₂ ) utilizing two custom-built red light sources. The treatment eliminates PrP^TSE signal in infectious mouse brain homogenate with efficiency that depends on light intensity but has a low effect on the overall protein content. Importantly, singlet oxygen (O₂ (¹ Δ_g )) is the only species significantly photogenerated by AlPcOH(SO₃ )₂ , and it is responsible for the PDI of prions. More intensive light conditions show not only higher O₂ (¹ Δ_g ) production but also decreases in AlPcOH(SO₃ )₂ photostability. Our findings suggest that PDI by AlPcOH(SO₃ )₂ -generated O₂ (¹ Δ_g ) represents a promising approach for prion inactivation that may be useful in future decontamination strategies for delicate medical tools.

Adsorption and decontamination of α-synuclein from medically and environmentally-relevant surfaces

The assembly and accumulation of α-synuclein fibrils are implicated in the development of several neurodegenerative disorders including multiple system atrophy and Parkinson's disease. Pre-existing α-synuclein fibrils can recruit and convert soluble non-fibrillar α-synuclein to the fibrillar form similar to what is observed in prion diseases. This raises concerns regarding attachment of fibrillary α-synuclein to medical instruments and subsequent exposure of patients to α-synuclein similar to what has been observed in iatrogenic transmission of prions. Here, we evaluated adsorption and desorption of α-synuclein to two surfaces: stainless steel and a gold surface coated with a 11-Amino-1-undecanethiol hydrochloride self-assembled-monolayer (SAM) using in-situ combinatorial quartz crystal microbalance with dissipation and spectroscopic ellipsometry. α-Synuclein was found to attach to both surfaces, however, increased α-synuclein adsorption was observed onto the positively charged SAM surface compared to the stainless steel surface. Dynamic light scattering data showed that larger α-synuclein fibrils were preferentially attached to the stainless steel surface when compared with the distributions in the original α-synuclein solution and on the SAM surface. We determined that after attachment, introduction of a 1N NaOH solution could completely remove α-synuclein adsorbed on the stainless steel surface while α-synuclein was retained on the SAM surface. Our results indicate α-synuclein can bind to multiple surface types and that decontamination is surface-dependent.

Human prion diseases: surgical lessons learned from iatrogenic prion transmission

The human prion diseases, or transmissible spongiform encephalopathies, have captivated our imaginations since their discovery in the Fore linguistic group in Papua New Guinea in the 1950s. The mysterious and poorly understood "infectious protein" has become somewhat of a household name in many regions across the globe. From bovine spongiform encephalopathy (BSE), commonly identified as mad cow disease, to endocannibalism, media outlets have capitalized on these devastatingly fatal neurological conditions. Interestingly, since their discovery, there have been more than 492 incidents of iatrogenic transmission of prion diseases, largely resulting from prion-contaminated growth hormone and dura mater grafts. Although fewer than 9 cases of probable iatrogenic neurosurgical cases of Creutzfeldt-Jakob disease (CJD) have been reported worldwide, the likelihood of some missed cases and the potential for prion transmission by neurosurgery create considerable concern. Laboratory studies indicate that standard decontamination and sterilization procedures may be insufficient to completely remove infectivity from prion-contaminated instruments. In this unfortunate event, the instruments may transmit the prion disease to others. Much caution therefore should be taken in the absence of strong evidence against the presence of a prion disease in a neurosurgical patient. While the Centers for Disease Control and Prevention (CDC) and World Health Organization (WHO) have devised risk assessment and decontamination protocols for the prevention of iatrogenic transmission of the prion diseases, incidents of possible exposure to prions have unfortunately occurred in the United States. In this article, the authors outline the historical discoveries that led from kuru to the identification and isolation of the pathological prion proteins in addition to providing a brief description of human prion diseases and iatrogenic forms of CJD, a brief history of prion disease nosocomial transmission, and a summary of the CDC and WHO guidelines for prevention of prion disease transmission and decontamination of prion-contaminated neurosurgical instruments.

Sequential Washing with Electrolyzed Alkaline and Acidic Water Effectively Removes Pathogens from Metal Surfaces

Removal of pathogenic organisms from reprocessed surgical instruments is essential to prevent iatrogenic infections. Some bacteria can make persistent biofilms on medical devices. Contamination of non-disposable equipment with prions also represents a serious risk to surgical patients. Efficient disinfection of prions from endoscopes and other instruments such as high-resolution cameras remains problematic because these instruments do not tolerate aggressive chemical or heat treatments. Herein, we develop a new washing system that uses both the alkaline and acidic water produced by electrolysis. Electrolyzed acidic water, containing HCl and HOCl as active substances, has been reported to be an effective disinfectant. A 0.15% NaCl solution was electrolyzed and used immediately to wash bio-contaminated stainless steel model systems with alkaline water (pH 11.9) with sonication, and then with acidic water (pH 2.7) without sonication. Two bacterial species (Staphylococcus aureus and Pseudomonas aeruginosa) and a fungus (Candida albicans) were effectively removed or inactivated by the washing process. In addition, this process effectively removed or inactivated prions from the stainless steel surfaces. This washing system will be potentially useful for the disinfection of clinical devices such as neuroendoscopes because electrolyzed water is gentle to both patients and equipment and is environmentally sound.

A direct assessment of human prion adhered to steel wire using real-time quaking-induced conversion

Accidental transmission of prions during neurosurgery has been reported as a consequence of re-using contaminated surgical instruments. Several decontamination methods have been studied using the 263K-hamster prion; however, no studies have directly evaluated human prions. A newly developed in vitro amplification system, designated real-time quaking-induced conversion (RT-QuIC), has allowed the activity of abnormal prion proteins to be assessed within a few days. RT-QuIC using human recombinant prion protein (PrP) showed high sensitivity for prions as the detection limit of our assay was estimated as 0.12 fg of active prions. We applied this method to detect human prion activity on stainless steel wire. When we put wires contaminated with human Creutzfeldt–Jakob disease brain tissue directly into the test tube, typical PrP-amyloid formation was observed within 48 hours, and we could detect the activity of prions at 50% seeding dose on the wire from 10^2.8 to 10^5.8 SD₅₀. Using this method, we also confirmed that the seeding activities on the wire were removed following treatment with NaOH. As seeding activity closely correlated with the infectivity of prions using the bioassay, this wire-QuIC assay will be useful for the direct evaluation of decontamination methods for human prions.

Mitigation of prion infectivity and conversion capacity by a simulated natural process--repeated cycles of drying and wetting

Prions enter the environment from infected hosts, bind to a wide range of soil and soil minerals, and remain highly infectious. Environmental sources of prions almost certainly contribute to the transmission of chronic wasting disease in cervids and scrapie in sheep and goats. While much is known about the introduction of prions into the environment and their interaction with soil, relatively little is known about prion degradation and inactivation by natural environmental processes. In this study, we examined the effect of repeated cycles of drying and wetting on prion fitness and determined that 10 cycles of repeated drying and wetting could reduce PrP^Sc abundance, PMCA amplification efficiency and extend the incubation period of disease. Importantly, prions bound to soil were more susceptible to inactivation by repeated cycles of drying and wetting compared to unbound prions, a result which may be due to conformational changes in soil-bound PrP^Sc or consolidation of the bonding between PrP^Sc and soil. This novel finding demonstrates that naturally-occurring environmental process can degrade prions.

Prion diseases such as chronic wasting disease and scrapie are emerging in North America at an increasing rate. Infectious prions are introduced into the environment from both living and dead animals where they can bind to soil. Little information is available on the effect of prion inactivation under conditions that would be found in the natural environment. In this study, we exposed both unbound and soil-bound prions to repeated cycles of drying and wetting to simulate ambient environmental conditions. We found evidence of prion inactivation in both unbound and soil bound prions. The influence of repeated cycles of drying and wetting are dependent on the prion strain and soil type used and, interestingly, prions bound to soil were more susceptible to inactivation. This is the first report of natural environmental processes mitigating prion infectivity. This data suggests that the total environmental prion load is a balance between input and natural clearance.

Persistence of ovine scrapie infectivity in a farm environment following cleaning and decontamination

Scrapie of sheep/goats and chronic wasting disease of deer/elk are contagious prion diseases where environmental reservoirs are directly implicated in the transmission of disease. In this study, the effectiveness of recommended scrapie farm decontamination regimens was evaluated by a sheep bioassay using buildings naturally contaminated with scrapie. Pens within a farm building were treated with either 20,000 parts per million free chorine solution for one hour or were treated with the same but were followed by painting and full re-galvanisation or replacement of metalwork within the pen. Scrapie susceptible lambs of the PRNP genotype VRQ/VRQ were reared within these pens and their scrapie status was monitored by recto-anal mucosa-associated lymphoid tissue. All animals became infected over an 18-month period, even in the pen that had been subject to the most stringent decontamination process. These data suggest that recommended current guidelines for the decontamination of farm buildings following outbreaks of scrapie do little to reduce the titre of infectious scrapie material and that environmental recontamination could also be an issue associated with these premises.

Role of peroxide ions in formation of graphene nanosheets by electrochemical exfoliation of graphite

This study demonstrates a facile, mild and environmentally-friendly sustainable (soft processing) approach for the efficient electrochemical exfoliation of graphite using a sodium hydroxide/hydrogen peroxide/water (NaOH/H2O2/H2O) system that can produce high-quality, anodic few-layer graphene nanosheets in 95% yield at ambient reaction conditions. The control experiment conducted using NaOH/H2O revealed the crucial role of H2O2 in the exfoliation of graphite. A possible exfoliation mechanism is proposed. The reaction of H2O2 with hydroxyl ions (HO(-)) leads to the formation of highly nucleophilic peroxide ions (O2(2-)), which play a crucial role in the exfoliation of graphite via electrochemical-potential-assisted intercalation and strong expansion of graphite sheets.

Harnessing prions as test agents for the development of broad-range disinfectants

The development of disinfectants with broad-range efficacy against bacteria, viruses, fungi, protozoa and prions constitutes an ongoing challenge. Prions, the causative agents of transmissible spongiform encephalopathies (TSEs) such as Creutzfeldt-Jakob disease (CJD) or its variant (vCJD) rank among the pathogens with the highest resistance to disinfection. Pilot studies have shown that procedures devised for prion disinfection were also highly effective against microbial pathogens. This fueled the idea to systematically exploit prions as test pathogens for the identification of new potential broad-range disinfectants. Prions essentially consist of misfolded, aggregated prion protein (PrP) and putatively replicate by nucleation-dependent, or seeded PrP polymerization. Recently, we have been able to establish PrP seeding activity as a quantitative in vitro indicator for the disinfection of 263K scrapie prions on steel wires used as surrogates for medical instruments. The seeding activity on wires re-processed in different disinfectants could be (1) biochemically determined by quantitative protein misfolding cyclic amplification (qPMCA), (2) biologically detected after qPMCA in a cell assay and (3) correctly translated into residual titres of scrapie infectivity. Our approach will substantially facilitate the identification of disinfectants with efficacy against prions as promising candidates for a further microbiological validation of broad-range activity.

Enzymatic degradation of PrPSc by a protease secreted from Aeropyrum pernix K1

Background

An R30 fraction from the growth medium of Aeropyrum pernix was analyzed for the protease that can digest the pathological prion protein isoform (PrP^Sc) from different species (human, bovine, deer and mouse).

Methodology/Principal Findings

Degradation of the PrP^Sc isoform by the R30 fraction and the purified protease was evaluated using the 6H4 anti-PrP monoclonal antibody. Fragments from the N-terminal and C-terminal of PrP^Sc were also monitored by Western blotting using the EB8 anti-PrP monoclonal antibody, and by dot blotting using the C7/5 anti-PrP monoclonal antibody, respectively. For detection of smaller peptides from incomplete digestion of PrP^Sc, the EB8 monoclonal antibody was used after precipitation with sodium phosphotungstate. Characterization of the purified active protease from the R30 fraction was achieved, through purification by fast protein liquid chromatography, and identification by tandem mass spectrometry the serine metalloprotease pernisine. SDS-PAGE and zymography show the purified pernisine plus its proregion with a molecular weight of ca. 45 kDa, and the mature purified pernisine as ca. 23 kDa. The purified pernisine was active between 58°C and 99°C, and between pH 3.5 and 8.0. The temperature and pH optima of the enzymatic activity of the purified pernisine in the presence of 1 mM CaCl₂ were 105°C ±0.5°C and pH 6.5±0.2, respectively.

Conclusions/Significance

Our study has identified and characterized pernisine as a thermostable serine metalloprotease that is secreted from A. pernix and that can digest the pathological prion protein PrP^Sc.

Doped diamond-like carbon coatings for surgical instruments reduce protein and prion-amyloid biofouling and improve subsequent cleaning

Doped diamond-like carbon (DLC) coatings offer potential antifouling surfaces against microbial and protein attachment. In particular, stainless steel surgical instruments are subject to tissue protein and resilient prion protein attachment, making decontamination methods used in sterile service departments ineffective, potentially increasing the risk of iatrogenic Creutzfeldt-Jakob disease during surgical procedures. This study examined the adsorption of proteins and prion-associated amyloid to doped DLC surfaces and the efficacy of commercial cleaning chemistries applied to these spiked surfaces, compared to titanium nitride coating and stainless steel. Surfaces inoculated with ME7-infected brain homogenate were visualised using SYPRO Ruby/Thioflavin T staining and modified epi-fluorescence microscopy before and after cleaning. Reduced protein and prion amyloid contamination was observed on the modified surfaces and subsequent decontamination efficacy improved. This highlights the potential for a new generation of coatings for surgical instruments to reduce the risk of iatrogenic CJD infection.

Quantitative detection and biological propagation of scrapie seeding activity in vitro facilitate use of prions as model pathogens for disinfection

Prions are pathogens with an unusually high tolerance to inactivation and constitute a complex challenge to the re-processing of surgical instruments. On the other hand, however, they provide an informative paradigm which has been exploited successfully for the development of novel broad-range disinfectants simultaneously active also against bacteria, viruses and fungi. Here we report on the development of a methodological platform that further facilitates the use of scrapie prions as model pathogens for disinfection. We used specifically adapted serial protein misfolding cyclic amplification (PMCA) for the quantitative detection, on steel wires providing model carriers for decontamination, of 263K scrapie seeding activity converting normal protease-sensitive into abnormal protease-resistant prion protein. Reference steel wires carrying defined amounts of scrapie infectivity were used for assay calibration, while scrapie-contaminated test steel wires were subjected to fifteen different procedures for disinfection that yielded scrapie titre reductions of ≤10(1)- to ≥10(5.5)-fold. As confirmed by titration in hamsters the residual scrapie infectivity on test wires could be reliably deduced for all examined disinfection procedures, from our quantitative seeding activity assay. Furthermore, we found that scrapie seeding activity present in 263K hamster brain homogenate or multiplied by PMCA of scrapie-contaminated steel wires both triggered accumulation of protease-resistant prion protein and was further propagated in a novel cell assay for 263K scrapie prions, i.e., cerebral glial cell cultures from hamsters. The findings from our PMCA- and glial cell culture assays revealed scrapie seeding activity as a biochemically and biologically replicative principle in vitro, with the former being quantitatively linked to prion infectivity detected on steel wires in vivo. When combined, our in vitro assays provide an alternative to titrations of biological scrapie infectivity in animals that substantially facilitates the use of prions as potentially highly indicative test agents in the search for novel broad-range disinfectants.

Fast, broad-range disinfection of bacteria, fungi, viruses and prions

Effective disinfectants are of key importance for the safe handling and reprocessing of surgical instruments. This study tested whether new formulations containing SDS, NaOH and 1-propanol (n-propanol) are simultaneously active against a broad range of pathogens including bacteria, fungi, non-enveloped viruses and prions. Inactivation and disinfection were examined in suspension and on carriers, using coagulated blood or brain homogenate as an organic contaminant. Coomassie blue staining was used to assess whether the formulations undesirably fixed proteins to rough surfaces. A mixture of 0.2 % SDS and 0.3 % NaOH in 20 % n-propanol achieved potent decontamination of steel carriers contaminated with PrP(TSE), the biochemical marker for prion infectivity, from 263K scrapie hamsters or from patients with sporadic or variant Creutzfeldt-Jakob disease. 263K scrapie infectivity on carriers was decreased by > or =5.5 logs. Furthermore, the formulation effectively inactivated poliovirus, hepatitis A virus and caliciviruses (including murine norovirus) in suspension tests. It also yielded significant titre reductions of bacteria (Enterococcus faecium, Mycobacterium avium; >6 logs), fungi (spores of Aspergillus niger; > or =5 logs) and poliovirus (>4 logs) embedded in coagulated blood on carriers. The formulation was not found to fix proteins more than was observed with water as the cleaning reagent. In conclusion, SDS, NaOH and n-propanol can synergistically achieve fast, broad-range disinfection.

Inactivation of animal and human prions by hydrogen peroxide gas plasma sterilization

Prions cause various transmissible spongiform encephalopathies. They are highly resistant to the chemical and physical decontamination and sterilization procedures routinely used in healthcare facilities. The decontamination procedures recommended for the inactivation of prions are often incompatible with the materials used in medical devices. In this study, we evaluated the use of low-temperature hydrogen peroxide gas plasma sterilization systems and other instrument-processing procedures for inactivating human and animal prions. We provide new data concerning the efficacy of hydrogen peroxide against prions from in vitro or in vivo tests, focusing on the following: the efficiency of hydrogen peroxide sterilization and possible interactions with enzymatic or alkaline detergents, differences in the efficiency of this treatment against different prion strains, and the influence of contaminating lipids. We found that gaseous hydrogen peroxide decreased the infectivity of prions and/or the level of the protease-resistant form of the prion protein on different surface materials. However, the efficiency of this treatment depended strongly on the concentration of hydrogen peroxide and the delivery system used in medical devices, because these effects were more pronounced for the new generation of Sterrad technology. The Sterrad NX sterilizer is 100% efficient (0% transmission and no protease-resistant form of the prion protein signal detected on the surface of the material for the mouse-adapted bovine spongiform encephalopathy 6PB1 strain and a variant Creutzfeldt-Jakob disease strain). Thus, gaseous or vaporized hydrogen peroxide efficiently inactivates prions on the surfaces of medical devices.

Prion adsorption to stainless steel is promoted by nickel and molybdenum

Prions are infectious agents resulting from the conversion of a normal cellular protein, PrP(C), to a misfolded species, PrP(Sc). Iatrogenic transmission of prions is known from surgical procedures involving stainless steel materials. Here, it was shown that stainless steel containing nickel and molybdenum binds PrP(Sc) more efficiently and transmits infection to cells in culture to a higher degree than if these elements are not present. Furthermore, both nickel and molybdenum alone adsorbed PrP(Sc), and nickel powder could be used to extract PrP(Sc) from dilute solutions, thus providing a simple approach to concentration of PrP(Sc). The fact that nickel and molybdenum in steel alloys increased the binding affinity, and bound infectivity, of PrP(Sc) is an important issue to consider in the manufacture of surgical instruments and abattoir tools.

New hospital disinfection processes for both conventional and prion infectious agents compatible with thermosensitive medical equipment

With the detection of prions in specific tissues in variant and sporadic Creutzfeldt-Jakob diseases, efficient decontamination for human transmissible spongiform encephalopathy (TSE) agents, that is compatible with medical equipment, has become a major issue. We previously described the cleavage of prions on exposure to copper (Cu) and hydrogen peroxide (H(2)O(2)) and have used this property to develop efficient prion decontamination processes. To validate this approach, in-vitro assays on genuine human and animal prions using both brain homogenates and steel wires to mimic contamination of medical equipment were conducted. In-vivo experiments using steel wire in the hamster 263 K model were then used to evaluate the effect on prion infectivity. Assays on classical pathogens following international norms completed these prion experiments. In-vitro data confirmed the full decontamination efficacy of H(2)O(2)/Cu on different TSE strains. Combination of Cu with peracetic acid, used for endoscope disinfection, also revealed improved prion decontamination. Animal assay demonstrated efficacy on TSE infectivity of H(2)O(2)/Cu alone or in combination with detergents (reduction factor > or =5.25 log(10)). Assays on classical pathogens confirmed the disinfection properties of the different processes. Taken together, these new disinfection processes are efficient for both conventional and prion infectious agents and are, compatible with thermosensitive medical equipment. They can be adapted to hospitals' and practitioners' routine use, and they present reduced risks for the environment and for healthcare professionals.

Can protein contamination be removed from hand endodontic instruments?

AIM

The aim of this study was to quantify total protein adhering to hand endodontic files and to measure and compare the efficacy of ultrasonic cleaning and washer-disinfectors, with and without presoaking, in protein removal from clinically contaminated endodontic files.

METHOD

Total protein contamination of the endodontic files was quantified using an assay reagent colorimetric method. Twelve general dental practitioners were recruited to collect clinically contaminated files. One hundred and fifty clinically contaminated files were allowed to air-dry in sterile plastic containers and a further 60 files were immersed, working end down, in enzymatic detergent immediately following clinical use. Thirty clinically contaminated files were tested for total protein contamination as a positive control. Sixty files were subjected to ultrasonic cleaning and 30 to processing in each of the washer-disinfectors. The presoaked files were divided into two groups of 30 for processing in the washer-disinfectors. A further group of brand-new, unused files were tested for protein contamination as a negative control.

RESULTS

Protein was present on 29 of the 30 new files tested. The median total mass of protein recovered from clinically contaminated hand endodontic instruments was 2.046 microg. The most effective method of presterilisation cleaning tested was a presoak in Alkazyme followed by processing in the Miele G7881 washer-disinfector.

CONCLUSION

The most effective method of presterilisation cleaning for hand endodontic files is a presoak in Alkazyme, an alkaline enzymatic detergent, followed by processing in a Miele G7881 washer-disinfector. This study provides up-to-date evidence that newer methods of presterilisation cleaning may fail to remove protein from endodontic hand instruments totally. This may have implications for all reusable dental instruments.

Detection of proteinase K resistant proteins in the urine of patients with Creutzfeldt-Jakob and other neurodegenerative diseases

Recent concern about the possible secondary spread of vCJD through blood transfusion and blood products has highlighted the need for a sensitive test for the identification of PrP(TSE/res) in clinical specimens collected in a non-invasive way. In addition, a more accurate estimate of the prevalence of pre-clinical vCJD in the population may be possible if there were a test that could be applied to easily available material such as urine. As a step towards this goal,the detection of putative PrP(TSE/res) in the urine of CJD patients has been improved, based on Proteinase K digestion of samples and western blotting. The modified western blot uses concentrated urine as a starting material. After proteolytic treatment followed by electrophoresis and western blotting, membranes are incubated with an anti-PrP antibody conjugated directly with horseradish peroxidase. This study was conducted on urine samples of CJD and other neurodegenerative disease affected individuals. Proteinase K resistant high molecular weight proteins were detected, which are suggested to be a complex of urinary PrP and immunoglobulin proteins. Whether urine can be used as a diagnostic tool for the detection of PrP could not be answered in this study.

Bovine spongiform encephalopathy

Bovine spongiform encephalopathy is an infectious disease of cattle that is transmitted through the consumption of meat-and-bone meal from infected cattle. The etiologic agent is an aberrant isoform of the native cellular prion protein that is a normal component of neurologic tissue. There currently are no approved tests that can detect BSE in live cattle.

Resistance of bovine spongiform encephalopathy (BSE) prions to inactivation

Distinct prion strains often exhibit different incubation periods and patterns of neuropathological lesions. Strain characteristics are generally retained upon intraspecies transmission, but may change on transmission to another species. We investigated the inactivation of two related prions strains: BSE prions from cattle and mouse-passaged BSE prions, termed 301V. Inactivation was manipulated by exposure to sodium dodecyl sulfate (SDS), variations in pH, and different temperatures. Infectivity was measured using transgenic mouse lines that are highly susceptible to either BSE or 301V prions. Bioassays demonstrated that BSE prions are up to 1,000-fold more resistant to inactivation than 301V prions while Western immunoblotting showed that short acidic SDS treatments reduced protease-resistant PrP(Sc) from BSE prions and 301V prions at similar rates. Our findings argue that despite being derived from BSE prions, mouse 301V prions are not necessarily a reliable model for cattle BSE prions. Extending these comparisons to human sporadic Creutzfeldt-Jakob disease and hamster Sc237 prions, we found that BSE prions were 10- and 10(6)-fold more resistant to inactivation, respectively. Our studies contend that any prion inactivation procedures must be validated by bioassay against the prion strain for which they are intended to be used.

Implications for Creutzfeldt-Jakob Disease (CJD) in Dentistry: a Review of Current Knowledge

This review explores our current understanding of the risks of (variant) Creutzfeldt-Jakob disease transmission via dental practice, and whether they merit the rigorous enforcement of improved standards of instrument cleaning and decontamination. The recognition of prions as novel infectious agents in humans has caused significant concern among the public and medical professionals alike. Creutzfeldt-Jakob disease (CJD) in humans has been shown to be transmissible via several routes, including transplantation, contaminated medical products, and via neurosurgery. While the likelihood of transmission via dentistry is undoubtedly very low, this may be amplified considerably by unknown risk factors, such as disease prevalence (particularly in the UK), altered tissue distribution of vCJD, and the failure of decontamination processes to address the inactivation of prions adequately. Since current diagnostic techniques are unable to detect PrPSc in human dental tissues, there is limited evidence for the presence of infectivity. Given these uncertainties, the control of risk by reinforced and improved decontamination practices seems the most appropriate response.

Prion stability and infectivity in the environment

The biology of normal prion protein and the property of infectivity observed in abnormal folding conformations remain thinly characterized. However, enough is known to understand that prion proteins stretch traditional views of proteins in biological systems. Numerous investigators are resolving details of the novel mechanism of infectivity, which appears to feature a protein-only, homologous replication of misfolded isoforms. Many other features of prion biology are equally extraordinary. This review focuses on the status of infectious prions in various natural and man-made environments. The picture that emerges is that prion proteins are durable under extreme conditions of environmental exposure that are uncommon in biological phenomena, and this durability offers the potential for environmental reservoirs of persistent infectivity lasting for years. A recurrent theme in prion research is a propensity for these proteins to bind to mineral and metal surfaces, and several investigators have provided evidence that the normal cellular functions of prion protein may include metalloprotein interactions. This structural propensity for binding to mineral and metal ions offers the hypothesis that prion polypeptides are intrinsically predisposed to non-physiological folding conformations that would account for their environmental durability and persistent infectivity. Similarly, the avidity of binding and potency of prion infectivity from environmental sources also offers a recent hypothesis that prion polypeptides bound to soil minerals are actually more infectious than studies with purified polypeptides would predict. Since certain of the prion diseases have a history of epidemics in economically important animal species and have the potential to transmit to humans, urgency is attached to understanding the environmental transmission of prion diseases and the development of protocols for their containment and inactivation.

Decontamination of surgical instruments from prions. II. In vivo findings with a model system for testing the removal of scrapie infectivity from steel surfaces

The unusual resistance of agents causing transmissible spongiform encephalopathies (TSEs) to chemical or thermal inactivation requires special decontamination procedures in order to prevent accidental transmission of these pathogens by surgical instruments. In the search for effective, instrument-compatible and routinely applicable decontamination procedures, a previous study [Lemmer, K., Mielke, M., Pauli, G. & Beekes, M. (2004). J Gen Virol 85, 3805-3816] identified promising reagents in an in vitro carrier assay using steel wires contaminated with the disease-associated prion protein, PrP(Sc). In the follow-up study presented here, these reagents were validated for their decontamination potential in vivo. Steel wires initially loaded with >or=3 x 10(5) LD(50) of 263K scrapie infectivity were implanted into the brains of hamsters after treatment for decontamination and subsequently monitored for their potential to trigger clinical disease or subclinical cerebral PrP(Sc) deposition within an observation period of 500 days. It was found that routinely usable reagents such as a commercially available alkaline cleaner (pH 12.2) applied for 1 h at 23 degrees C or for 10 min at 55 degrees C and a mixture of 0.2 % SDS and 0.3 % NaOH (pH 12.8) applied for 5 or 10 min at 23 degrees C achieved removal of 263K scrapie infectivity below the threshold of detection (titre reduction of >or=5.5 log(10) units). The increasing use during the past few years of similar model systems by different research groups will facilitate comparison and integration of findings on the decontamination of steel surfaces from prions. Methods identified as highly effective in the 263K steel wire model need to be validated for human TSE agents on different types of instrument surfaces.

Quantitative bioassay of surface-bound prion infectivity

The unconventional nature of the infectious agent of prion diseases poses a challenge to conventional infection control methodologies. The extra neural tissue distribution of variant and sporadic Creutzfeldt-Jakob disease has increased concern regarding the risk of prion disease transmission via general surgical procedures and highlighted the need for decontamination procedures that can be incorporated into routine processing. This chapter describe a quantitative method for assessing the prionocidal activity of chemical and physical decontamination methods against surface-bound prion infectivity.

Enzymatic detergent treatment protocol that reduces protease-resistant prion protein load and infectivity from surgical-steel monofilaments contaminated with a human-derived prion strain

The unconventional nature of the infectious agent of prion diseases poses a challenge to conventional infection control methodologies. The extraneural tissue distribution of variant and sporadic Creutzfeldt–Jakob disease has increased concern regarding the risk of prion disease transmission via general surgical procedures and highlighted the need for decontamination procedures that can be incorporated into routine processing. In this study, the ability of preparations of enzymatic medical instrument cleaners to reduce the infectivity associated with a rodent-adapted strain of human prion disease, previously reported to be resistant to decontamination, was tested. Efficient degradation of the disease-associated prion protein by enzymatic cleaning preparations required high treatment temperatures (50–60 °C). Standard decontamination methods (1 M NaOH for 1 h or autoclaving at 134 °C for 18 min) reduced infectivity associated with the human-derived prion strain by less than 3 log10 LD50. In contrast, a 30 min treatment with the optimized enzymatic cleaning preparation protocols reduced infectivity by more than 3 log10 LD50 and when used in conjunction with autoclave cycles eliminated detectable levels of infectivity. The development of prion decontamination procedures that are compatible with routine cleaning and sterilization of medical and surgical instruments may reduce the risk of the transmission of prion disease in general surgery.

Characterization of a proteolytic enzyme derived from a Bacillus strain that effectively degrades prion protein

AIMS

The purpose of this paper was to screen candidate bacterial strains for the production of proteases suitable for application to the degradation of pathogenic forms of prion protein (PrP(Sc)). This paper describes the biochemical characteristics and proteolytic activity of the isolated protease.

METHODS AND RESULTS

After screening more than 200 bacterial proteases for keratinolytic activity, we identified a Bacillus stain that produced a protease exhibiting high-degradation activity against a scrapie PrP(Sc). Sequence analysis indicated that this serine-protease belonged to the Subtilisin family and had optimum pH and temperature ranges of 9-10 and 60-70 degrees C. Western blotting analysis revealed that the protease was also capable of decomposing bovine spongiform encephalopathy-infected brain homogenate. In addition, the protease was demonstrated to degrade dried PrP(Sc) that had become firmly attached to a plastic surface considerably more effectively than proteinase K or PWD-1, a previously reported keratinase.

CONCLUSIONS

These results indicate that the isolated protease exhibited higher activity for PrP(Sc) degradation compared with other proteases examined.

SIGNIFICANCE AND IMPACT OF THE STUDY

This protease could be used under moderate conditions for the decontamination of precision instruments that are susceptible to PrP(Sc) contamination.

Investigations of a prion infectivity assay to evaluate methods of decontamination

Prions are unique infectious agents which have been shown to be transmitted iatrogenically through contaminated surfaces. Surface contamination is a concern on reusable medical devices and various industrial surfaces, but there is currently no standard, accepted model to evaluate surface prion decontamination. In this report, a set of both in vitro and in vivo methods were investigated based on the contamination of surface through artificial exposure to infected brain. An in vitro surface contamination protocol was developed with subsequent biochemical detection of the prion protein (PrPres). In parallel, the in vivo investigations included the contamination of different types of surface materials (stainless steel or plastic wires) with different prion strains (scrapie strain adapted to hamsters 263K or bovine spongiform encephalopathy strain adapted to mouse 6PB1). The in vivo models with various prion strains and brain homogenate dilutions reproducibly transmitted the disease and a relationship was established between the infectivity titre, the transmission rate and the incubation period. Moreover, the in vivo models were studied for their ability to demonstrate the efficacy of heat and chemical-based decontamination methods, with similar results. The in vivo scrapie method described is proposed as a standard to evaluate existing and developing prion decontamination technologies.

Accumulation of pathological prion protein PrPSc in the skin of animals with experimental and natural scrapie

Prion infectivity and its molecular marker, the pathological prion protein PrP^Sc, accumulate in the central nervous system and often also in lymphoid tissue of animals or humans affected by transmissible spongiform encephalopathies. Recently, PrP^Sc was found in tissues previously considered not to be invaded by prions (e.g., skeletal muscles). Here, we address the question of whether prions target the skin and show widespread PrP^Sc deposition in this organ in hamsters perorally or parenterally challenged with scrapie. In hamsters fed with scrapie, PrP^Sc was detected before the onset of symptoms, but the bulk of skin-associated PrP^Sc accumulated in the clinical phase. PrP^Sc was localized in nerve fibres within the skin but not in keratinocytes, and the deposition of PrP^Sc in skin showed no dependence from the route of infection and lymphotropic dissemination. The data indicated a neurally mediated centrifugal spread of prions to the skin. Furthermore, in a follow-up study, we examined sheep naturally infected with scrapie and detected PrP^Sc by Western blotting in skin samples from two out of five animals. Our findings point to the skin as a potential reservoir of prions, which should be further investigated in relation to disease transmission.

Transmissible spongiform encephalopathies (TSEs), or prion diseases, are fatal neurodegenerative diseases affecting the central nervous system. According to the prion hypothesis, TSEs are caused by proteinaceous infectious particles (“prions”) that consist essentially of PrP^Sc, an aberrant form of the prion protein with a pathologically altered folding and/or aggregation structure. Scrapie of sheep, chronic wasting disease (CWD) of deer, bovine spongiform encephalopathy (BSE) of cattle, and variant Creutzfeldt-Jakob disease (vCJD) of humans are prominent examples of acquired prion diseases. To further pinpoint the peripheral tissues that could serve as reservoirs of prions in the mammalian body and from which these pathogens could be potentially disseminated into the environment and transmitted to other individuals, we examined the skin of hamsters perorally challenged with scrapie and of naturally infected scrapie sheep for the presence of PrP^Sc. We show that PrP^Sc can accumulate in the skin at late stages of incubation, and that the protein is located primarily in small nerve fibres within this organ. The question of whether the skin may also provide a reservoir for prions in CWD, BSE, or vCJD, and the role of the skin in relation to the natural transmission of scrapie in the field needs further investigation.

Electro-elution, a novel method to remove transmissible spongiform encephalopathy-associated PrPSc from stainless steel surgical instruments

Iatrogenic transmission of transmissible spongiform encephalopathies (TSEs) has been demonstrated via surgical instruments and there is concern over the efficacy of conventional decontamination techniques used to reprocess reusable instruments. This paper describes the development of a novel cleaning method, 'electro-elution', to remove TSE disease-specific abnormal protein PrP(Sc) from the surface of stainless steel surgical instruments. The electro-elution process subjects the stainless steel instrument to an electrical current in the presence of an electrolytic buffer to remove protein deposits. Stainless steel discs were contaminated with infectious brain homogenate and subjected to a range of conditions to determine the ability of electro-elution to remove the deposits. To determine whether there was any residual PrP(Sc) remaining on the disc after electro-elution, a novel detection method, 'direct blotting', was also developed. Direct blotting utilizes a process of passive transfer of proteins directly from the surface of the instrument to a proteophilic membrane for detection. Our study shows that electro-elution has the ability to effectively remove, and possibly degrade, disease-associated PrP(Sc) from the surface of stainless steel surgical instruments.

Impact of vCJD on blood supply

Variant Creutzfeldt-Jakob disease (vCJD) is an at present inevitably lethal neurodegenerative disease which can only be diagnosed definitely post mortem. The majority of the approximately 200 victims to date have resided in the UK where most contaminated beef materials entered the food chain. Three cases in the UK demonstrated that vCJD can be transmitted by blood transfusion. Since BSE and vCJD have spread to several countries outside the UK, it appears advisable that specific risk assessments be carried out in different countries and geographic areas. This review explains the approach adopted by Germany in assessing the risk and considering precautionary measures. A fundamental premise is that the feeding chain of cattle and the food chain have been successfully and permanently cleared from contaminated material. This raises the question of whether transmissions via blood transfusions could have the potential to perpetuate vCJD in mankind. A model calculation based on actual population data showed, however, that this would not be the case. Moreover, an exclusion of transfusion recipients from blood donation would add very little to the safety of blood transfusions, but would have a considerable impact on blood supply. Therefore, an exclusion of transfusion recipients was not recommended in Germany.

Effect of Prion Decontamination Protocols on Nickel-Titanium Rotary Surfaces

Decontamination of instruments is a prerequisite for their potential reuse but may affect surface integrity. Hence, the effect of prion removal protocols on 7 brands of nickel-titanium files was investigated. Baseline debris scores were determined under magnification after staining with van Gieson's solution. After shaping root canals in vitro, rotaries were mechanically and ultrasonically cleaned followed by immersion for 24 hours in 2 M sodium hydroxide (NaOH), 6 M CH(5)N(3), or 3% sodium hypochlorite (NaOCl); control files were stored dry. After sterilization, files were again stained and evaluated. Two of seven file brands demonstrated significantly higher baseline debris scores compared to final scores. Uniformly, debris could not be completely removed; there were no significant differences among groups. After immersion in NaOCl, 27.8% of instruments showed corrosion; however, no deterioration after immersion in the other solutions was found in the other groups. Regarding corrosion, no significant difference was found between brands. Based on these findings, single use of nickel-titanium rotaries appears beneficial.

Structural characterization of β-sheeted oligomers formed on the pathway of oxidative prion protein aggregation in vitro

The pathology of transmissible spongiform encephalopathies (TSEs) is strongly associated with the structural conversion of the cellular prion protein (PrPC) into a misfolded isoform (PrPSc) that assembles into amyloid fibrils. Since increased levels of oxidative stress have been linked to prion diseases, we investigated the metal-induced oxidation of human PrP (90-231). A novel in vitro conversion assay based on aerobic incubation of PrP in the presence of elemental copper pellets at pH 5 was established, resulting in aggregation of highly beta-sheeted prion proteins. We show for the first time that two discrete oligomeric species of elongated shape, approx. 25 mers and 100 mers, are formed on the pathway of oxidative PrP aggregation in vitro, which are well characterized regarding shape and size using small-angle X-ray scattering (SAXS), dynamic light scattering (DLS), and electron microscopy (EM). Considering that small oligomers of highly similar size have recently been reported to show the highest specific infectivity within TSE-infected brain tissues of hamsters, the novel oligomers observed in this study are interesting candidates as agent causing neurodegenerative and/or self-propagating effects. Moreover, our results significantly strengthen the theory that oxidative stress might be an influence that leads to substantial structural conversions of PrP in vivo.

Quality of surgical instruments

INTRODUCTION

Many surgeons will have encountered the scissors that would not cut, and the artery clip that comes off in a deep difficult location, but it would be reasonable to assume that new instruments should be of assured quality. This study reports the surprising findings of a local quality control exercise for new instruments supplied to a single trust.

MATERIALS AND METHODS

Between January 2004 and June 2004, all batches of new surgical instruments ordered by the Central Sterile Supplies Department of St Bartholomew's and the Royal London Hospitals were assessed by three clinical engineers, with reference to British Standards (BS) requirements.

RESULTS

Of 4800 instruments examined, 15% had potential problems. These included 116 with machining burrs and debris in the teeth of the tissue-holding regions, 71 defects of ratcheted instruments, 34 scissors with deficient cutting action, and 35 tissue forceps protruding guide pins. In addition, 254 instruments did not have a visible manufacturer's mark.

CONCLUSIONS

This study demonstrates the value of local quality control for surgical instruments. This is of importance in an increasingly hazard-conscious environment, where there are concerns over instrument sterilisation, surgical glove puncture and the potential for transmission of blood-borne and prion diseases.