Sterilization physical indicators

Hospital sterilizer loads vary in composition, thus the challenge presented to the test organism can vary considerably, depending on the type and contents of packages in which they are placed. The benefits of a standardized test-pack constmction and test protocol are obvious, and such recommendation is made by AAMI for steam and ethylene oxide sterilizers (11). More recentiy in European (CEN) and International (ISO) standards, biological indicators are considered as additional information supplemental to the measurement of physical parameters. Indeed, for sterilization using moist heat (steam), the biological indicator information is not considered to be relevant. 

Monitoring of the sterilization process canbe achieved by the rrse of physical, chemical or biological indicators of sterilizer performance. Such indicators are frequently employed in combination. 

Biological castles are employed during heat penetration situations in order to demonstrate the degree of process lethality provided by the sterilization cycle. Calibrated biological indicators utilized for this purpose function as bioburden models providing data that can be utilized to calculate Fq or substantiate and supplement physical temperature measurements obtained from thermocouples. 

Another SOP category related to the physical facility is environmental control. All plants must be kept free of rodents and insects. Such an SOP will indicate acceptable materials to be used, precautions to prevent product and personnel contamination, frequency, and area-monitoring procedure. In some operations, such as an area to manufacture sterile products, there are requirements for control of air temperature, humidity, flow rates and patterns, and particulate matter. These SOPs require steps such as checks to be performed, including temperature reading and frequency, maintenance to be performed, such as changing air filters and frequency, recording instrument checks, and calibration, such as for temperature and frequency. A prototype SOP is illustrated in Figure 6. 

Knowledge of the physical conditions near an object we desire to sterilize suggests that conditions are appropriate for the intended result, but cannot truly establish that fact. Biological indicators positioned in or on the surfaces we intend to sterilize provide a clarity of result that is hard to dispute. Properly sited the BI must experience the lethal effect of the sterilizing agent in order to succumb. Predicting its death, or worse yet explaining away its survival on the basis of some physical measurement, is wholly inappropriate. 

In the dormant spore state, endospores are resistant to a wide variety of chemical and physical stresses such as UV and gamma radiation, desiccation, temperature and pressure extremes, and attack by toxic agents (67-70). As they are resilient to most sterilization procedures, bacterial spores are used in several industries as biological indicators (71,72). Certain species can even survive the vacuum, extreme temperatures, and radiation of space (73,74), making them the focus of research concerning planetary protection, panspermia (transfer of life from one... 

In practical terms a pass in the Test for Sterility should not be perceived to be of any more significance than any other successful measure of compliance with microbiological or physical standards or controls applicable to the manufacture of sterile products. A pass in the Test for Sterility must not be allowed to overrule any failure to comply with other environmental or control standard(s) because it is quite possible to pass the Test and still have a significant number of non-sterile units in the batch. On the other hand, a failed Test for Sterility is likely to be a good indicator of a genuine problem that has not been disclosed by some other microbiological or physical means. 

Each heat sterilization cycle should be recorded by appropriate equipment with suitable accuracy and predsion, e.g., on a time/temperature chart with a suitably large scale. The temperature should be recorded from a probe at the coolest part of the load or loaded chamber, this point having been determined during the validation the temperature should preferably be checked against a second independent temperature probe located at the same position. The chart, or a photocopy of it, should form part of the batch record. Chemical or biological indicators may also be used but should not take the place of physical controls. 

Before any sterilization process is adopted its suitability for the product and its efficacy in achieving the desired sterilising conditions in all parts of each type of load to be processed should be demonstrated by physical measurements and by biological indicators where appropriate. The validity of the process should be verified at scheduled intervals, at least annually, and whenever significant modifications have been made to the equipment Records should be kept of the results. 

Each heat sterilization cycle should be recorded on a temperature-time chart or by other suitable automatic means. The time-temperature record should form part of the batch record. Chemical or biological indicators may be used in addition to but should not take the place of physical controls. 

Biological indicators (i.e. preparations of bacteria cultures, usually spore of selected resistant strains) are must less reliable than physical monitoring methods, except in Ethylene Oxide Sterilization. 

The duration and temperature of heat sterilization must be recorded. The temperature must be determined at the coldest site in the lot or the chamber. The observations form a part of the Lot Production Record. Chemical or biological indicators may be used but not in place of physical controls. 

The manufacture of drugs intended to be sterile should be performed in areas specially designed and constructed, as indicated in Article 7.C. Whenever the different operations are not physically separated and there is a possibility that unsteriiized and sterilized products might be confused, all containers of batches of products for sterilization should bear a clear indication of whether or not their contents have been sterilized. 

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