Electron Micrographs of Bacterial Cultures Infected with Bacteriophage

Abstract

Now that we have learned to recognize individual virus particles through the electron microscopy of purified suspensions it has become practical to approach the more important question of how these particles are produced within the cells they infect. Probably bacteria with their bacteriophage provide the simplest virus system immediately accessible to existing technics. This is partly because sperm-like bacteriophage particles 1 , 2 can easily be recognized even in the presence of other particles of similar submicroscopic size and partly because bacteria are hosts small enough to allow an electron microscopic examination of both their surface and their internal structures.

To gain a satisfactory understanding of the steps involved in bacteriophage-production it is essential to be able to photograph sensitive bacteria under the conditions in which they grow and become infected. We have found that this can be done by studying replicas made of the surfaces of agar plates incubated for various periods of time after inoculation with bacteria and bacteriophage. The technic we have been using to obtain such replicas is essentially the same as that recently described by Hillier and Baker. 3 It has consisted in covering the surface of a bacteriophage-bacterial growth with a dilute solution of collodion or other plastic and floating the resulting film off onto a water surface for further manipulation. Like Hillier and Baker we have found that organisms are retained by the film made in this way but our preparations have also shown numerous impressions of individual bacteria. This has made it possible to see in a single film details of both surface and internal structure.

Formvar dissolved in ethylene dichloride will yield good replicas but best results have been obtained with collodion. Collodion, USP, diluted with 5 to 6 volumes of normal amyacetate, carefully spread over the