Glutaraldehyde and ortho-phthalaldehyde (OPA) are widely used as the active ingredients of high level disinfectants for heat-sensitive, semicritical medical instruments. However, both of these chemicals have limitations in their spectrum of antimicrobial activity. Glutaraldehyde disinfectants are poorly mycobactericidal, and require impractically long exposure times to kill spore-forming bacteria. OPA disinfectants kill many types of mycobacteria in practical exposure times, but require 32hours to pass the Association of Official Analytical Chemists (AOAC) sporicidal test, and do not claim to be sterilants. These could be serious limitations that contribute to the formation of biofilms in endoscopes, after which the endoscopes are difficult to disinfect. The objective of our research was to discover a disinfectant formulation, based on aldehydes, that killed mycobacteria and spore-forming bacteria in a practical exposure time and temperature.

Solutions of glutaraldehyde or OPA were prepared with various concentrations of alcohols, sodium and potassium salts, chelating agents, and detergents at alkaline pH values, and tested against cultures of mycobacteria and spore-forming bacteria to find a formulation that would kill these bacteria in practical exposure times at 20°C or 25°C.

Concentrations of≤20% w/w isopropanol and≤8% potassium acetate in combination with≤3.5% w/w glutaraldehyde at alkaline pH values killed 6log₁₀ of mycobacteria within 10minutes at 20°C. Similar combinations killed 6log₁₀ of Bacillus subtilis in suspension within 30minutes at 25°C, and B subtilis within 60minutes at 20°C. The sporicidal activity of OPA was not increased by combination with isopropanol and potassium acetate salts.

Aldahol high-level disinfectant (US FDA K041360), a formulation of 3.5% glutaraldehyde in combination with 20% w/w isopropanol and 8% potassium acetate, kills mycobacteria within 10minutes at 20°C and kills 6log₁₀ of cultures of the spore-forming bacteria B subtilis within 60minutes at 20°C.