The mycobactericidal efficacy of ortho-phthalaldehyde and the comparative resistances of Mycobacterium bovis, Mycobacterium terrae, and Mycobacteriumchelonae

OBJECTIVES: To assess the mycobactericidal efficacy of an agent relatively new to disinfection, ortho-phthalaldehyde (OPA) and to compare the resistan ces of three Mycobacterium species. Mycobacterium bovis (strain BCG) was co mpared with Mycobacterium chelonae and Mycobacterium terrae to investigate the feasibility of using either of the latter two species in tuberculocidal testing. M chelonae (a rapid grower) and M terrae (an intermediate grower) both grow faster and are less virulent than M bovis (a slow grower). DESIGN: The quantitative suspension protocol specified by the Environmental Protection Agency (EPA), the Tuberculocidal Activity Test Method (EPA test ), was used throughout this study. Standard suspensions of all three specie s were prepared in a similar manner. Two suspensions of M bovis, created in different laboratories, were used. These were tested against two concentra tions of alkaline glutaraldehyde to provide reference data. Two concentrati ons of OPA were evaluated against all mycobacterial test suspensions. Four replicates of each organism-disinfectant combination were performed. RESULTS: Results were assessed by analysis of variance. M terrae was signif icantly more resistant to 0.05% OPA than either M bovis or M chelonae. At 0 .21% OPA, M terrae was slightly more susceptible than one test suspension o f M bovis, but not significantly different from the other. M chelonae was s ignificantly less resistant than the other species at both OPA concentratio ns. At their respective minimum effective concentration OPA achieved a 6-lo g(10) reduction of M bovis in nearly one sixth the time required by glutara ldehyde (5.5 minutes vs 32 minutes). CONCLUSIONS: These data, along with other recent studies, lend support to t he idea that M terrae may be a suitable test organism for use in the tuberc ulocidal efficacy testing of disinfectants. They also confirm the relativel y rapid tuberculocidal activity of OPA.