Gerald E. McDonnell - Antisepsis, Disinfection, and Sterilization

The effects of various types of physical and chemical variables can be tested by using suspension methods. Physical effects include the product temperature and pH, while chemical effects include the biocide concentration or dilution, formulation type, and interfering substances, such as organic (e.g., serum and blood) and inorganic (e.g., heavy metals and hard water) soils. These effects are often important considerations in the practical use of the biocidal product.

Examples of some standardized suspension tests are given in Table 1.18.

Surface tests are used to verify the antimicrobial activity of a product or process on a test surface. This is an important consideration in the use of many surface antiseptics, disinfectants, and sterilants. Tests can be considered to belong to three types: carrier tests, simulated-use testing, and in-use testing.

In carrier methods, the test microorganism is inoculated onto a defined carrier material, in the presence or absence of interfering soils, and is then exposed to the biocidal process or product. The carrier material can simply consist of a coupon (a piece) of any test surface (including paper, stainless steel, glass, or plastic) or a defined test carrier; for example, stainless steel and porcelain penicylinders are widely used in the United States to test the surface-disinfectant efficacies of products. For antiseptic testing, sections of ex vivo skin have been used as test surfaces. Following exposure, the test coupons are retrieved (with neutralization if required) and tested for the survival of the test microorganism. This can also be performed qualitatively (by immersion into growth medium and incubation, followed by observation of growth or no growth) or quantitatively (by elution of the test culture and direct enumeration or fraction-negative determination, as described in section 1.4.2.1). Examples of various types of standardized carrier tests are given in Table 1.19. Some of the most widely used carrier tests are defined biological and chemical indicators used for various sterilization process tests, which are described in more detail in section 1.4.2.3.

TABLE 1.18 Examples of standardized suspension tests

a AOAC, Association of Official Analytical Chemists; ASTM, American Society for Testing and Materials; USP, U. S. Pharmacopeia; EN, European Norm, from the CEN (European Committee for Standardization).

Simulated-use tests are also laboratory based; an artificial inoculum is applied to a surface to simulate the actual use of the product or process in a typical application. Examples are the use of an artificial inoculum on the skin or on various surfaces, such as medical devices. In these methods, it is important to validate the test methods, including the inoculation method and neutralization and recovery methods, to ensure that they are reproducible and reliable. As well as direct application of the test culture to a surface, in some situations, the microbial culture can be inoculated onto a carrier or inserted into the test equipment at a worst-case location (e.g., in the internal channel of a lumened device), exposed to the product or process, and recovered for evaluation. Recovery methods can include elution, swabbing, air filtering, and use of contact plates. Examples of various simulated-use test guidelines and standards are given in Table 1.20.

TABLE 1.19 Examples of standardized carrier tests

a AOAC, Association of Official Analytical Chemists; ASTM, American Society for Testing and Materials; EN, European Norm, from the CEN (European Committee for Standardization).