Yeast-suspension as soiling matter in disinfectant testing

Area of Science:

• Microbiology
• Antimicrobial Efficacy Testing

Background:

• Disinfectant efficacy testing often simulates 'dirty' conditions using organic materials.
• Yeast suspensions are sometimes used to mimic these organic loads.
• The interaction between yeast and disinfectants requires further investigation.

Purpose of the Study:

• To investigate the effect of sterile yeast suspensions on the antimicrobial activity of disinfectants.
• To determine if yeast can enhance the efficacy of Chloramine T, Chloramine B, and sodium hypochlorite.
• To identify the mechanism behind any observed enhancement.

Main Methods:

• Kelsey-Sykes capacity-test was employed.
• Antimicrobial activity was assessed against fungi (Candida albicans, Aspergillus fumigatus, Geotrichum candidum, Penicillium sp., Rhodotorula rubra) and bacteria.
• Tests were conducted under both 'clean' and 'dirty' (simulated with yeast suspension) conditions.
• Comparison was made between Chloramine T, Chloramine B, and sodium hypochlorite.
• The role of a diffusible factor from yeast cells was explored.

Main Results:

• Sterile yeast suspensions significantly enhanced the fungicidal effect of Chloramine T and Chloramine B against specific fungi (C. albicans, A. fumigatus, G. candidum, Penicillium sp.).
• This enhancement was not observed with Rhodotorula rubra or tested bacteria.
• A diffusible factor from yeast cells was responsible for the enhanced effect.
• Heating or prolonged standing of yeast suspensions produced this factor.
• Normal horse serum reduced the effect of Chloramine T, as expected.

Conclusions:

• Sterile yeast suspensions can lead to an overestimation of Chloramine T and Chloramine B fungicidal efficacy.
• This may result in incorrect disinfectant use-dilution concentrations, especially when relying solely on 'dirty' condition tests.
• Careful consideration of test conditions and interfering substances is crucial for accurate disinfectant evaluation.