Kinetics of the tuberculocidal response by alkaline glutaraldehyde in solution and on an inert surface

Single cell suspensions of BCG and Mycobacterium tuberculosis were exposed to 2% alkaline glutaraldehyde solution (pH 8.0) and the rate of kill measured at intervals up to 30 min. Residual glutaraldehyde was neutralized with freshly prepared 1% sodium bisulphite. The rate of kill was directly proportional to the temperature and independent of the inoculum size whether the organism was tested in suspension or attached to an inert surface. Glutaraldehyde was slightly more bactericidal for the virulent M. tuberculosis than for the attenuated BCG. A substantial proportion of the mycobacterial population on an inert surface floated off during its exposure to the glutaraldehyde solution but the 'floaters' were killed at an equivalent rate to the attached bacilli. Complete sterility of a standardized suspension of M. tuberculosis could not be achieved within the 10 min period specified by the tuberculocidal assay, although it was usually attained within 20 min.