ASTM E1054-08

The effectiveness of antimicrobial agents incorporated into disinfectants, sanitizers, and antiseptics is measured by their ability to kill microorganisms within a specified contact time. Hence, accurate determination of antimicrobial effectiveness requires complete and immediate inactivation (neutralization) of the antimicrobial agent. Inefficient or incomplete neutralization will permit killing or inactivation of microorganisms to continue beyond the experimental exposure time, resulting in an overestimation of antimicrobial activity.

The neutralization methods commonly used in antimicrobial effectiveness evaluations are chemical inactivation, dilution, and filtration. All critical parameters of an antimicrobial effectiveness evaluation—for example, media, equipment, microorganism(s), and temperature of solutions—must be duplicated when evaluating a neutralization procedure to be used.

The neutralization evaluation must include at least three replications (five replications in Section 9) so that a statistical analysis of the recovery data can be performed. The number of replicates used in the evaluation depends on the statistical significance required for the expected results, the variability encountered in the data, and the relative effectiveness of the neutralization procedure.

A limitation of these evaluation procedures is that they use microorganisms that have not been exposed to an antimicrobial agent. Under experimental conditions, cells exposed to neutralization procedures are likely to be damaged to different degrees by the antimicrobial agent. Sublethal injury may be a factor in recovery, and the role of the neutralization procedure in recovery of injured organisms should be examined. This method is not intended to assess injured organism recovery.

Note 3—Ideally, all microorganisms used in the antimicrobial effectiveness evaluation should be tested in the neutralization assay. However, representative organisms may be selected for testing, as judged appropriate by the investigator. The investigator is cautioned that failure to identify neutralizer efficacy and toxicity for all microorganisms could result in exaggerated microbial reductions in an antimicrobial effectiveness evaluation. Also, for a study testing multiple antimicrobial formulations, and in which samples will contain multiple species of microorganisms (for example, skin flora) that are exposed to the formulations, a single procedure and/or combination of agents suitable for neutralizing the antimicrobial activities of the multiple formulations must be used for testing.

1.1 These test methods are used to determine the effectiveness of procedures and agents for inactivating (neutralizing, quenching) the microbicidal properties of antimicrobial agents, and to ensure that no components of the neutralizing procedures and agents, themselves, exert an inhibitory effect on microorganisms targeted for recovery.

Note 1—Knowledge of microbiological and statistical techniques is required for these procedures. These methods are not suitable when testing the virucidal activity of microbicides (see Test Method E 1482).

1.2 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.

1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.