Phage Susceptibility of Encapsulated Lactobacillus casei

Abstract

ONE of the principal factors which determines the susceptibility of a given bacterium to attack by bacteriophage is the availability of specific surface receptor sites. Numerous investigators have observed that encapsulated bacteria are generally phage resistant, and it has been assumed that the capsular layer, interposed as a physical barrier between receptor and phage, acts as a non-specific inhibitor of phage adsorption. In partial confirmation of this role, Maxted¹ showed that although phage resistant group A streptococci possessed a hyaluronic acid capsule, treatment with hyaluronidase destroyed the capsule and rendered the cells phage-sensitive. It is not clear, however, from this and other reports² whether the susceptibility of non-encapsulated cells was due to the availability of receptor sites permitting increased adsorption or to some other factor permitting increased virus penetration and lysis of the bacterial cell. This report presents evidence that in the related homolactic organism, L. casei, the specific surface receptor sites are present in varying amounts on both encapsulated and non-encapsulated cells but that the loss of the capsular material, either by mutation or mechanical removal, renders the previously resistant cell sensitive to lysis by phage.