ISO specifies requirements and provides guidance on the enumeration and microbial characterization of the population of viable microorganisms. ISO. Second edition. Sterilization of medical devices — Details of the software products used to create this PDF file can be found in the. ANSI/AAMI/ISO .. medical-site.info The adoption of ISO as an American National Standard was initiated by the.
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Summary: Specifies general criteria to be applied in the estimation of the population of viable microorganisms on a medical device or. STANDARD. ISO. Third edition. Reference number. ISO (E). This is a free 6 page sample. Access the full version online. Normative references. EN ISO Expression of results. Furthermore the EN ISO does not specify requirements for the microbiological.
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A secure PDF contains features that enforce existing copyright laws by preventing reproduction or distribution to other users. The preparation of control charts does not strictly depend upon any underlying assumed distribution. Experience gained in fitting empirical distributions to such data sets suggests that the following two transformations of individual counts might be suitable.
Means will tend to have a more symmetrical distribution than individual values. Biofilm could form on or in product in contact with liquids. S The limits used for bioburden are based upon historical data for product.
Based upon successive test results. A predetermined course of action must be taken when specified limits are exceeded. The frequency of determinations of bioburden should allow detection of changes in bioburden. The quantities that are plotted on control charts are the mean and standard deviation or range. The selection of a method for determination of bioburden should consider the possible occurrence of biofilm on or in product.
If a mathematical distribution can be fitted to a given set of data. Data derived from bioburden determinations for a given product might not precisely follow a well-recognized mathematical distribution. Sampling may be performed at a frequency based on time e. Transformation of raw data may further improve the applicability of a standard Shewhart control chart. In the absence of a fit to a mathematical distribution. Medical devices incorporating tissue have a potential for biofilm occurrence.
In the absence of such historical data. This can be done in a qualitative manner by grouping the measurements to form frequency tables and charts. In these circumstances. Determinations 'from a group will vary within the group of items. Before statistical calculations can be performed on data derived from bioburden determinations.
Since bioburden counts of zero may be observed. S Graphical representation of data collected over time can be useful in distinguishing actual trends from sampling variability. If a sufficient number of historical data is not available for a given product. The suggested transformation then becomes: In some instances.
Each of these different techniques can be used to establish a possible shift from the usual random spread of results and to highlight out-of-specification results. A commonly observed characteristic of the frequency distributions of data derived from determinations of bioburden is that distributions are extremely skewed and frequently show extremely long tails.
Where appropriate. The limits can be revised when more data become available. There is a number of techniques for trending which can be applied to bioburden. Shewhart control charts. These trending techniques can be. The examination of data derived from determinations of bioburden for a wide range of products illustrates the variability of such data.
Upon completion. When bioburden data are analysed for use in a quality-related deCision. For low or intermediate data. Control limits for a standard Shewhart control chart of the average bioburden can be established after a sufficient number of historical counts have been collected for a product.
If they are thought to be other than laboratory error or the occasional high values found in the manufacturing process. Graphical representation can also indicate that a significant change in the microbiological population has occurred even though the bioburden values reside within the preset limits.
Any data identified as outliers should be discarded in setting limits. Data identified as unusually large or small should be investigated. Special statistical techniques may have to be developed for individual cases. B] Figure B. The individual responsible for the conduct of such determinations should use the knowledge of the raw materials.
The individual responsible for the conduct of such determinations should take account of the particular circumstances under which the determinations are made in deciding the sampling rate. Microorganisms in biofilms can exhibit increased resistance to sterilization processes. Desiccation can be the cause of significant decreases in numbers of microorganisms and should be considered in the selection of storage conditions and storage times.
If delay in transfer is unavoidable. Care should be taken to ensure that the counts obtained are representative. For example.
To remove microorganisms. Biofilms can be initiated within minutes and can develop to a much greater extent on medical devices incorporating tissue or on used devices. An indication that a biofilm is present can be obtained during validation of the removal technique if repeated high microbial counts are recorded during repetitive recovery.
ReCiprocating paddles operate on the bag forCing the eluent through and around the item. A biofilm is a structure in which microorganisms are encapsulated in a matrix that adheres strongly to surfaces. A surfactant may be used to enhance recovery but it should be recognized that surfactants at high concentrations could be inhibitory to the growth of microorganisms.
The variables and ways of controlling them should be considered when selecting a treatment and devising suitable conditions of treatment.
The presence of disaggregated material can render enumeration of microorganisms difficult. In such instances. The origin of the contamination will also influence the degree of adhesion. The maximum storage time should be specified. Additional treatment. If practicable. Manual shaking might be used but its effectiveness can vary depending on the operator.
Vortex mixing B. The size of added glass beads. The vortex produced will depend upon the pressure applied manually. It can be destructive to some medical devices. Liquid flow can be induced by B. Microorganisms can also be inactivated by ultrasonication.
Consideration should be given to limiting the number of items to be processed concurrently as some of the sonication power can be reduced through shielding. Either the vessel and contents are treated in an ultrasonic bath or an ultrasonic probe is immersed in the contained eluent.
The container to be used.
NOTE B. Variations in the vortex can cause variable removal. Some of the microorganisms that are collected can become trapped in the matrix of the swab itself and therefore not be detected. The sampling material may be soluble or insoluble. Transport media can be used to transfer removed microorganisms for enumeration and diluents used to obtain suspensions containing microorganisms in countable numbers.
The composition should be such that proliferation or inactivation of microorganisms does not occur. The item is blended or chopped for a specified time. They are also useful when a large area is to be sampled.
All rights reseNed The swab is transferred to diluent and agitated to remove microorganisms from the swab. The recovery efficiency can be improved in some circumstances by first moistening the surface and then swabbing with a dry swab.
In selecting a diluent or eluent. Contact plates and slides are generally only useful on flat or at least regular surfaces. A surfactant such as polysorbate Tween 80 may be added to eluents and diluents. Preparation of isotonic solutions of soluble materials prior to counting This list is not exhaustive.
A NOTE concentration of between 0. The method is particularly appropriate for product having bioburden of low mean number. Its principal uses are in the food and water industries where it is used with liquid. This method may be applicable when the bioburden is low and the product configuration suitable.
Results are directly related to the area in contact with the solidified culture medium. The plate or slide can then be incubated to produce colonies that are enumerated. The appropriate concentration to be used with any particular treatment needs careful selection because foaming can occur. In some cases. If microbicidal or microbiostatic substances are present in the eluent. From the frequency of the occurrence of positive tests within a set of replicates.
When a sufficient volume of eluent is available. The key requirement for the application of the MPN method is the random distribution of microbial population throughout the product under investigation.
Care should be exercised in order to avoid excessive backpressures. Enumeration of the viable microorganisms in the suspension can be undertaken using one of the techniques described below.
A filter of appropriate nominal pore size not greater than 0. This could lead to an underestimate of the bioburden. In an MPN exercise. If microbicidal or microbiostatic substances are present.
Some types of membrane can absorb or release substances that could inhibit the growth of microorganisms. Colonies produced on the surface of the membrane filter can be counted and isolated for microbial characterization. Due to the design of the apparatus and the use of capillary tubing and small volumes.
The membrane filter and the eluent should be compatible. The suspension is spread at a decreasing rate in a spiral track from the centre of the culture plate to the periphery. After suitable incubation.
This number should be such that each viable microorganism is able to express itself as a visible colony without being affected adversely by its near neighbours. These include the measurement of metabolic activity e. It is an example of an approach that may be used to assess a technique for compliance with 6.
Alternative techniques should be of adequate sensitivity to detect low levels of microorganisms. Normally the lower limit of numbers detected exceeds CFU. This limit does not necessarily apply to bioburden determinations for medical devices where the bioburden is low. If the removal technique uses an eluent. Such methods are termed "indirect" because. The recovered microorganisms are counted at the end of this treatment.
Enumeration of the microorganisms gives a measure of the effects of the physical forces. Pharmacopoeias detail the microorganisms that can be used.
The effects of these forces on the bioburden determination should be assessed. In order to establish the effect of the eluent. The number of microorganisms used should be approximately After a defined period.
If a medical device incorporates an antimicrobial substance that could be released slowly into the medium. See B. In this test. It may be necessary to introduce a dilution.
The fraction of the total number of colonies can be calculated for each product item examined and used to obtain a recovery efficiency. After each repetition. The exact relationship between the number of microorganisms recovered and the actual number on the product cannot always be demonstrated. The exact number of repetitions applied will depend upon a number of factors including the nature of the product.
Results accumulated from the consecutive recoveries are compared. Preliminary experiments can be used to establish the number of repetitions to be applied. This process of applying the technique to the same product item may be repeated on a defined number of occasions.
This technique is the one normally used to determine bioburden. Each product should be individually subjected to the defined technique. Sometimes it is referred to as "exhaustive recovery". Clause C. It should be noted. This can be achieved by either of the following. S The principle underlying this approach is that the method of bioburden determination should be repeated until there is no significant increase in the accumulated number of microorganisms recovered.
The colonies formed on incubation are counted. These data relate to five replicate medical devices.
The use of vegetative microorganisms is difficult in practice because loss of viability can occur on drying. Colony counts determined from repetitive treatment for replicates of a medical device Product item Treatment 1 2 3 4 5 1 60 50 70 55 45 2 10 12 5 2 3 3 1 0 2 0 0 4 0 1 0 0 1 Agar overlay 2 1 2 1 0 73 64 79 58 49 Total colony count C.
The nature of certain medical devices may preclude the use of agar overlay. When selecting a microorganism to be used in validating by product inoculation. Preliminary experiments may be necessary to establish the appropriate dilution. This decision will be influenced by the use to be made of the data. The microorganisms can be vegetative cells but the most common approach utilizes aerobic bacterial spores.