Differentiation of the Rapidly Growing M. Balnei, M. Fortuitum, and Saprophytic Mycobacteria by Means of a Three-Day Phenolphthalein Sulfatase Test

A Comparative Study of Techniques

¹ Director, Tuberculosis Research, Medical Research Laboratory, Veterans Administration Hospital

The present investigation was undertaken to study further the usefulness of a three-day phenolphthalein sulfatase test for the differentiation of the rapidly growing M. balnei, M. fortuitum, and saprophytic acid-fast bacilli. Two different test methods were compared.

It was found that, with the liquid medium test technique and a 0.0005M concentration of the enzyme substrate, tripotassium phenolphthalein disulfate, all of the M. fortuitum strains could be differentiated from all of the other mycoabacteria. With a substrate concentration of 0.002M all of the saprophytic mycobacteria could be separated from all of the M. balnei and M. fortuitum strains and most of the M. balnei organisms could be differentiated from most of the M. fortuitum strains.With the solid medium test procedure and a substrate concentration of 0.000125M, all of the M. fortuitum strains could be differentiated from all of the other mycobacteria. With a substrate concentration of 0.0005M all of the saprophytic mycobacteria could be separated from all of the M. baleni and M. fortuitum strains and most of the M. balnei organisms could be differentiated from most of the M. fortuitum strains.

On the basis of the present findings, the liquid medium test technique has proved somewhat more useful than the solid medium test method because of the more clear-cut results which have been obtained in the majority of the tests performed. Additional study will be required before this can be determined definitely.

Thus far, the phenolphthalein sulfatase test has proved to be a rapid and useful screening tool for the differentiation of these three groups of mycobacteria.