Effectiveness of Twenty Germicides Against Five Strains of C. difficile spores, With and Without Calf Serum, at Several Exposure Times

Abstract

Background:Clostridioides difficile is a major cause of antibiotic-associated colitis and the most common healthcare-associated pathogen in the United States. Interrupting the known transmission mechanisms of C. difficile in hospitals requires appropriate hand hygiene, disinfection of potentially contaminated surfaces, and patient equipment. However, only limited data are available on the effectiveness of germicides against various strains of C. difficile, with and without fetal calf serum, and at multiple exposure times. For this reason, we undertook the following evaluation to determine the effectiveness of germicides. Methods: The effectiveness of the sporicidal activity of the germicides against 5 strains of C. difficile was evaluated using a quantitative carrier test, a standard of ASTM International developed by Sattar et al. In this protocol, metal carriers (1 cm diameter 0.7 mm thick) were inoculated with 10 L spore suspension, containing ~103 or 106 C. difficile spores, and we then exposed them to 50 L germicide for 1, 5, 10, or 20 minutes. The following C. difficile strains were used in these studies: ATCC strains 9689; J9; BI-9; 630; and CF-4. To determine whether C. difficile spore susceptibility was similar to other spores, we also tested Bacillus atrophaeus spores, ATCC strain 19659. Fetal calf serum (FCS) was used to simulate organic matter. Results: In general, high-level disinfectants (eg, OPA, glutaraldehyde), chemical sterilants (eg, peracetic acid), and high concentrations of chlorine (>5,000 ppm) were generally sporicidal (>3 log10 reduction) in 5–10 minutes (and sometimes 1 minute). This level of sporicidal activity was demonstrated for the various strains of C. difficile spores and B. atrophaeus spores (Table 1). There did not appear to be any significant differences in inactivation of C. difficile spores (BI-9 strain) in the presence or absence of FCS (Table 2). Discussion: The sporicidal activity of disinfectants is critical because such formulations are routinely used to eliminate the risk associated with noncritical and semicritical instruments and environmental surfaces. Our data suggest that immersion in most (but not all) high-level disinfectants for 10 minutes is likely to be successful in eradicating C. difficile spores (>4 log10 reduction) from semicritical equipment (eg, endoscopes). Additionally, high concentrations of chlorine and some high-level disinfectants will kill C. difficile spores in 1 or 2 minutes.Funding: NoneDisclosures: Drs. Rutala and Weber are consultants to PDI (Professional Disposable International)