Action of antibiotics on avian tubercle bacilli studied with the electron microscope.

Abstract

THE method described by Brieger and Cosslett1 of growing tubercle bacilli on the ‘Formvar’ film of a stainless steel electron microscope grid has been modified for use with liquid media. In this form the method has been found suitable for a study of the action of antibiotics upon growing tubercle bacilli. In order to prevent the fluid medium contaminating the inoculated surfaces, the grids are placed in contact with filter paper which rests on a cotton-wool support in a small dish 5 cm. in diameter and 2 cm. deep. The cotton-wool is kept moist by being thoroughly soaked in the medium. One dish can take up to twenty grids. The grids are inoculated with a drop of bacillary suspension using a fine platinum loop. If the drop does not stay on the surface of the grid, it is assumed that the holes in the ‘Formvar’ film are too large and the grid is discarded. The grids on which the drops remain are considered to be inoculated with similar numbers of bacilli. The dishes are incubated at 37.5° C. and grids removed at various intervals for inspection. Each grid is floated on sterile distilled water to remove any medium adhering to the lower surface, fixed by floating on 5 per cent formalin for 30 min., and washed again to remove any excess fixative. Throughout the procedure care is taken that the inoculated surface of the grid remains undisturbed. This is an essential condition for the study of variations in growth-rate.