The Mycobactericidal Efficacy of Ortho-Phthalaldehyde and the Comparative Resistances of Mycobacterium bovis, Mycobacterium terrae, and Mycobacterium chelonae

Abstract

AbstractObjectives:To assess the mycobactericidal efficacy of an agent relatively new to disinfection, ortho-phthalaldehyde (OPA) and to compare the resistances of threeMycobacteriumspecies.Mycobacterium bovis(strain BCG) was compared withMycobacterium chelonaeandMycobacterium terraeto investigate the feasibility of using either of the latter two species in tuberculocidal testing.M chelonae(a rapid grower) andM terrae(an intermediate grower) both grow faster and are less virulent thanM 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 species were prepared in a similar manner. Two suspensions ofM bovis,created in different laboratories, were used. These were tested against two concentrations of alkaline glutaraldehyde to provide reference data. Two concentrations 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 terraewas significantly more resistant to 0.05% OPA than eitherM bovisorM chelonae.At 0.21% OPA,M terraewas slightly more susceptible than one test suspension ofM bovis,but not significantly different from the other.M chelonaewas significantly less resistant than the other species at both OPA concentrations. At their respective minimum effective concentration, OPA achieved a 6-log10 reduction ofM bovisin nearly one sixth the time required by glutaraldehyde (5.5 minutes vs 32 minutes).Conclusions:These data, along with other recent studies, lend support to the idea thatM terraemay be a suitable test organism for use in the tuberculocidal efficacy testing of disinfectants. They also confirm the relatively rapid tuberculocidal activity of OPA.