Abstract
The present paper deals with the studies of growth inhibitory power of galactose against the mutabile type variant of Murase made by the quantitative titration availing paper disk method.
Liquid agar containing the living organisms of the mutabile type variant of E. coli was poured on the agar plate and solidified. Mathod of the preparation of this agar plate is essentially the same as that employed in the cup method for the titration of penicillin unit. Namely, 0.01 cc of a galactose solution was pipeted out on a paper disk of 6 mm in diameter which was then placed on the above agar plate and incubated at 37°C for 24 hours in order to determine the diameter of growth inhibition zone around the disk.
Various factors possibly influencing the growth inhibiting power of galactose such as the number of organisms inoculated, kind of medium used, pH of the medium, , duration of time after placing the paper disk and before incubation, and the period of incubation etc were investigated in order to find out the minimal quantity of galactose necessary to give a positive growth inhibition zone.
Experimental results revealed that when 2 cc of a peptone water culture of the M variant is mixed with 98 cc of 1% peptone agar and 4 cc of this mixture was pured on 5 cc of peptone agar and solidified and then the paper disk is placed on it, such a small quantity of galactose as 1/640, 000 g con give a quite distinct growth inhibition zone after an incubation period of 24 hours.
Diameter of the inhibition zone was found to increase in proportion to the increase in the concentration of galactose.
Moreouer, some spontaneously derived galactose resistant variants develop in the zone of growth inhibition.
Further discussions on the present study will follow in the second report of this series.
