Thermostable adenylate kinase technology: a new process indicator and its use as a validation tool for the reprocessing of surgical instruments.

Adenylate kinase (tAK), a thermostable enzyme, was assessed as a possible means of providing a quantitative measure of cleaning efficacy suitable for validating the performance of an automated washer disinfector (AWD) during routine use. Two indicator formulations were developed using either a commercially available washer disinfector soil or a protein-based soil. Each indicator consisted of 100 microg (in test soil) of tAK dried on to a steel or plastic surface. These indicators were placed in each basket of a washer disinfector and processed alongside soiled surgical instruments during a standard day's operation. After processing, remaining tAK activity was detected using a rapid enzyme assay (2 min detection time) in a handheld hygiene monitor. The amount of tAK remaining on each indictor after a full AWD cycle was found to range from 0.1 to 0.4 ng, which represented a mean log(10) removal of 5.8+/-0.3. There was no statistical difference in the residual tAK activity between individual runs or the position of the indicator in the machine. The tAK indicator was also used to analyse the protein removal within each component of the wash cycle. These results demonstrated that all phases of the wash process contributed to the removal of the protein load, with the main wash alone being responsible for 3.6-4.0 log(10) reductions in protein activity. We propose that a quantitative cleaning index using such rapid readout indicator devices would provide a valuable addition to the methodologies for validating cleaning processes.

Quantitative measurement of the efficacy of protein removal by cleaning formulations; comparative evaluation of prion-directed cleaning chemistries.

The stability of the infectious agent causing variant Creutzfeldt-Jakob disease (vCJD) has highlighted the importance of cleaning surgical instruments for controlling potential spread of iatrogenic CJD. In this study, thermostable adenylate kinases (tAKs) in test soil were coated on to stainless steel and these surrogate agents used to evaluate the efficacy of a range of cleaning chemistries in a bench-top washer disinfector (btWD), or as a pre-soak either with or without subsequent treatment by btWD. Two tAKs were tested initially for ease of removal, the most persistent being Sulfolobus acidocaldarius-derived tAK which was used for evaluating the cleaning chemistries. Conventional chemistries were generally more effective when used in a btWD than as pre-soaks. Cleaning efficacy improved when pre-soaks were followed by treatment with intermediate performing enzymes, demonstrating greater than additive effect on residual tAK activity. Three of the four prion-directed chemistries reduced residual tAK activity to below the limit of quantification (LoQ) by more than 4.8 log(10); <175pg tAK remaining as a pre-soak alone. A conventional alkaline cleaning product also reduced residual tAK activity to below the LoQ but only when used in a btWD. tAK soil dried on to the device was removed less efficiently than tAK soil still moist on the device, with a 320-fold and 28-fold increase in residual tAK activity for pre-soak and btWD, respectively. The study demonstrated the potential for a tAK indicator to describe the effectiveness of protein removal using different chemistries or treatment processes.

Proteolytic fragmentation reveals the oligomeric and domain structure of porcine aminopeptidase A.

Aminopeptidase A (glutamyl aminopeptidase; EC 3.4.11.7) has been cloned from porcine brain and kidney cortex cDNA libraries and the complete primary sequence of the enzyme deduced. This predicts a type II integral membrane protein of 942 amino acids with 14 potential N-linked glycosylation sites and a His-Glu-Xaa-Xaa-His zinc binding motif. Aminopeptidase A was purified from porcine kidney cortex by a combination of anion exchange and hydrophobic interaction chromatographies following its release from the membrane by trypsin. The purified protein migrated as three major polypeptides on SDS-polyacrylamide gel electrophoresis of M(r) 147,000, 107,000, and 45,000. N-Terminal sequencing revealed that both the Mr 147,000 and 107,000 polypeptides had the same N-terminal sequence resulting from cleavage of aminopeptidase A by trypsin at the Lys-42-Asp-43 bond just outside the membrane-spanning hydrophobic region. Immunoelectrophoretic blot analysis following electrophoresis under nonreducing conditions revealed that the trypsin-cleaved form of the enzyme no longer migrated as a disulfide-linked dimer, placing the interchain disulfide link N-terminal to Lys-42. N-Terminal sequencing of the M(r) 45,000 polypeptide in the purified preparation of aminopeptidase A revealed that it resulted from cleavage at the Asn-602-Gly-603 bond by an endogenous protease. This posttranslational proteolytic cleavage occurred in porcine kidney cortex microvillar membranes but not in porcine intestinal microvillar membranes. Incubation of purified porcine kidney aminopeptidase N (membrane alanyl aminopeptidase; EC 3.4.11.2) with trypsin resulted in a similar fragmentation pattern to that observed in aminopeptidase A, suggesting that these and other members of the type II membrane-spanning zinc aminopeptidase family may have two distinct domains: an N-terminal domain, containing the zinc binding site and residues identified as being involved in catalysis, and a C-terminal domain of unknown function, that are separated by a protease-susceptible region.