5.1 This practice describes a procedure for preparing and storing a suspension of C. difficile spores that meets the following acceptance criteria: (1) spore titer of approximately 5.0×10⁸ spores/mL, (2) spore purity of ≥95 %, and (3) a mean log₁₀ reduction (LR) value >5.0 for 3 carriers exposed to 5000 ppm and a mean LR of <3.0 for 3 carriers exposed to 1500 ppm sodium hypochlorite. These acceptance criteria are necessary in order to use the spore suspension to evaluate the performance of antimicrobial formulations using Test Method E3218.

1.1 This practice specifies the procedures for producing and storing standardized suspensions of Clostridioides difficile spores for the evaluation of the sporicidal activity of antimicrobial formulations using the Quantitative Method for Testing Antimicrobial Agents against Spores of C. difficile on Hard, Non-porous Surfaces or other procedures.

1.2 This practice may involve hazardous materials, chemicals, and microorganisms and should be performed only by persons with formal training in microbiology.

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

1.4 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.

1.5 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.