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Modified AOAC three step method (officialmethod 2008.05): consolidation of fractions B and C
Vipin K Rastogi1, Lisa S Smith, Lalena Wallace
1U.S. Army, Edgewood Chemical Biological Center, BioDefense Team, R & T Directorate, Aberdeen Proving Grounds, MD 21010, USA.
Journal of AOAC International
|November 29, 2013
Summary
A modified Three Step Method (TSM) simplifies sporicidal efficacy testing by combining recovery steps. This streamlined approach maintains equivalent results to the original TSM, saving time and resources.
Area of Science:
- Microbiology
- Disinfection and Sterilization
- Analytical Chemistry
Background:
- The AOAC Quantitative Three Step Method (TSM) is a validated standard for assessing liquid sporicidal efficacy against Bacillus spores on various surfaces.
- The TSM involves recovering viable spores from inoculated carriers in three distinct fractions (A, B, and C) after chemical exposure.
- Current TSM procedures require multiple tubes and steps, presenting opportunities for procedural simplification.
Purpose of the Study:
- To comparatively evaluate the current AOAC Quantitative Three Step Method (TSM) against a modified version (mTSM).
- To determine if consolidating the sonication (B) and agitation (C) recovery fractions in the mTSM yields equivalent sporicidal efficacy data.
- To support a modification of the TSM to streamline the testing procedure.
Main Methods:
- Inoculated carriers (glass, steel, wood, ceramic) with Bacillus spores were exposed to sodium hypochlorite sporicidal agents.
- Viable spores were recovered using both the standard TSM (fractions A, B, C) and the modified TSM (consolidated B and C fractions).
- Mean log density (LD) and log reduction (LR) values were calculated and compared between the TSM and mTSM for control and treated carriers.
Main Results:
- No significant differences were observed in mean log densities (LD) for control carriers between the TSM and mTSM across all tested materials.
- Log reduction (LR) values for treated carriers demonstrated comparable sporicidal efficacy between the TSM and mTSM.
- The modified TSM (mTSM) successfully consolidated recovery fractions B and C without compromising data integrity.
Conclusions:
- The modified Three Step Method (mTSM) is equivalent to the original TSM for determining sporicidal efficacy.
- Consolidating recovery fractions B and C in the mTSM offers a simplified and resource-efficient alternative to the standard TSM.
- The mTSM modification is supported by comparative data and can be adopted to improve the efficiency of sporicidal testing.
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