Abstract
At the time of investigating the degree of acid-fastness among various types of Mycobacteria, the present authors were attracted by the fact that a smear of M. smegmatis, which was left on the desk near the sunny window, has lost remarkably the acid-fast stainability. This was assumed to be an effect of ultraviolet light.
Smears of single cell suspension of about 50 germs per field were dried and irradiated from 10cm distance for various time periods employing a germicidal lamp, Matsuda GL 15, light of which is consisted mainly of the wave lergth of 2537 Å. The irradiance was assumed to be about 1, 200μw/cm2/min. according to Azuma et al's irradiance curve.
Irradiated smears were flame fixed, stained with victoriablue solution by heating, and were rinsed in a 0.1% nitric acid-70% ethanol for 20 minutes. Then they were blotted with filter paper and were counterstained with a 10 fold dilution of Ziehl's phenolfuchsin for 10 to 20 seconds. Bacterial numbers in 20 fields at random were counted on 3 slides each per one strain to the respective irradiation time to make total bacterial number approximately to 2, 500∼3, 500.
Results in Exp. 1 revealed that the loss of acid-fastness varied to a considerable extent in the different strains or types (Table 1). The loss of acid-fastness demonstrated S-shaped curves as the function of irradiation time (Fig. 1). The average irradiation times required for the complete loss of acid-fastness calculated in Exp. 2 employing 129 stock cultures were shown in Table 2. Difference in the irradiation time between the virulent and the avirulent mammalian types was repeatedly demonstrated and extremely interesting phenomenon.
After UV irradiation for sufficient long time periods, the bacterial cells of all types were no more restainable by the ordinary acid-fast staining procedures as shown in Exp. 3 suggesting that the cell wall became more porous by the destruction due to the UV energy.
Relation between the acid-fastness and Gram positiveness was investigated in Exp. 4. The results revealed that the gram positiveness was not deprived even from saprophytic Mycobacteria by the prolonged UV irradiation for about 20 hours suggesting that the acid-fastness and the gram positiveness are of quite different mechanism.
