Comparative sporicidal effect of liquid chemical germicides on three medical devices contaminated with spores of Bacillus subtilis

Background: The relatively limited variety of surfaces and geometries challenged in current sporicidal testing reduces the predictive value of these analyses when extrapolated to the wide variety of medical devices. The unknown spore load being challenged and the qualitative nature (growth/no growth) of those tests further prevent precise comparison among liquid chemical disinfectants. Hence, the relative activity of different chemical substances has not been clearly established, hindering selection of the best agent for each clinical situation. Methods: A micromethod was developed to assess sporicidal activity against Bacillus subtilis spores deposited on three different medical devices: carbon-steel dental burs silicone-rubber medical catheters, and titanium-alloy dental abutment screws. The spore load on each device and the recovery after three analytical steps were quantitatively assessed with spores radiolabeled with carbon 14 menthionine. Results: The killing of 2 to 7 × 106 spores loaded on three different devices and exposed to glutaraldehyde, fomaldehyde, copper ascorbate, hydrogen peroxide, peracetic acid, sodium hypochlorite, or phenol for 30 minutes at 20° C ranged from a 103-fold decrease for 10% hydrogen peroxide to zero decrease for 5% phenol. Our results suggest that the nature of the surface being challenged may affect the sporicidal activity of some chemical agents. Conclusion: The quantitative data presented allow comparison of the sporicidal effect of different liquid chemical agents. These findings may help prevent an overestimation of sporicidal activity and possible transmission of pathogens from the surface of improperly decontaminated medical devices.