Inhibition of phage infection in capsule-producing <i>Streptococcus thermophilus</i> using concanavalin A, lysozyme and saccharides

Abstract

Lactic cultures that produce capsular polysaccharides are widely used in the dairy industry. However, little information is available on their phage-cell interactions. Concanavalin A (Con A), lysozyme, and
saccharides were investigated for their ability to modify phage-cell interactions in such a manner as to inhibit phage infection. The ability of phage to infect cells was determined by measuring acid
production in Elliker broth. Acid production by capsule-producing Streptococcus thermophilus was inhibited less by bacteriophage when cells were pretreated with Con. A than was acid production by a
capsule-free variant. The presence of 0.5 mg/ml lysozyme in Elliker broth significantly reduced phage infection. However, there was no increased effect when lysozyme and Con A were combined in the
growth medium. The addition of 5 g/L of glucosamine to Elliker broth also inhibited phage infection. The results of this study indicate that it is possible to reduce phage infection of capsule-forming S.
thermophilus by blocking or modifying phage adsorption sites.