IADR Abstract Archives
Comparison of Two Methods for Evaluating Efficacy of DUWL Disinfectants
Objectives: To investigate and compare efficacy of APHA Standard Methods of Heterotrophic Plate Count 9215C (Spread Plate) and 9215D (Membrane Filter) methods for evaluating dental unit waterline (DUWL) disinfectants.
Methods: Three bacterial challenge suspensions (BCS) were selected; two were retrieved from DUWLs single colony (BCS-A and BCS-B) and one contained Pseudomonas aeruginosa (ATCC 700829) and Klebsiella pneumoniae (ATCC 700831) (BCS-C), following the guidelines of ISO 16954:2015. Four DUWL disinfectants DentaPure 365B cartridge and Liquid Ultra Solution (Crosstex, Hauppauge, NY); Citrisil Shock and Citrisil Blue (Sterisil, Palmer Lake, CO) were prepared following manufacturer’s instructions and challenged with bacterial suspensions (103-104/mL). Samples were evaluated at 1, 4 and 24 hours post-treatment using Spread Plate and Membrane Filter Methods on R2A agar. Plates were incubated at 22oC for 5-7days for colony forming unit (CFU/mL).
Results: All four DUWL disinfectants demonstrated antimicrobial activities. DentaPure cartridge and Liquid Ultra Solution eradicated three BCS after contact and throughout three evaluating time points, and microbial reduction was >99.9% in both assay methods. The efficacy of silver ion based Citrisil Shock and Citrisil Blue varied to different BCSs. Both disinfectants showed no reduction of BCS-A at 1-hour and the inhibitory effect was time-related; after 24-hour contact the microbial reductions were 84.6% to 99.3% in the Spread Plate method and 72.3% to >93.9% in the Membrane Filter method. After 24-hour microbial reductions of BCS-B and BCS-C were >99.9% in both assay methods. In general, Spread plate data showed a higher bacterial reduction than the Membrane Filter method; the average difference was 8.9%, indicating possible residual bactericidal effect of disinfectants in the Spread Plate method.
Conclusions: Membrane filter method is preferred as it does not appear to be affected by potential residual bactericidal effect of disinfectants, which needs to be considered in evaluating the efficacy of DUWL disinfectants.
Methods: Three bacterial challenge suspensions (BCS) were selected; two were retrieved from DUWLs single colony (BCS-A and BCS-B) and one contained Pseudomonas aeruginosa (ATCC 700829) and Klebsiella pneumoniae (ATCC 700831) (BCS-C), following the guidelines of ISO 16954:2015. Four DUWL disinfectants DentaPure 365B cartridge and Liquid Ultra Solution (Crosstex, Hauppauge, NY); Citrisil Shock and Citrisil Blue (Sterisil, Palmer Lake, CO) were prepared following manufacturer’s instructions and challenged with bacterial suspensions (103-104/mL). Samples were evaluated at 1, 4 and 24 hours post-treatment using Spread Plate and Membrane Filter Methods on R2A agar. Plates were incubated at 22oC for 5-7days for colony forming unit (CFU/mL).
Results: All four DUWL disinfectants demonstrated antimicrobial activities. DentaPure cartridge and Liquid Ultra Solution eradicated three BCS after contact and throughout three evaluating time points, and microbial reduction was >99.9% in both assay methods. The efficacy of silver ion based Citrisil Shock and Citrisil Blue varied to different BCSs. Both disinfectants showed no reduction of BCS-A at 1-hour and the inhibitory effect was time-related; after 24-hour contact the microbial reductions were 84.6% to 99.3% in the Spread Plate method and 72.3% to >93.9% in the Membrane Filter method. After 24-hour microbial reductions of BCS-B and BCS-C were >99.9% in both assay methods. In general, Spread plate data showed a higher bacterial reduction than the Membrane Filter method; the average difference was 8.9%, indicating possible residual bactericidal effect of disinfectants in the Spread Plate method.
Conclusions: Membrane filter method is preferred as it does not appear to be affected by potential residual bactericidal effect of disinfectants, which needs to be considered in evaluating the efficacy of DUWL disinfectants.