Host-controlled Modification and Restriction of Phages in Coagulase-negative Staphylococci

Summary: Three host-controlled modification and restriction systems occurring among coagulase-negative staphylococci belonging to the Staphylococcus subgroup II are described. The phage patterns, observed by typing the staphylococci with a provisional typing set of eighteen phages, are mainly determined by these host specificity systems. A strain, which was not restrictive to the phages, did not become restrictive after lysogenization with any of the eighteen phages. Infection of a restricting host with 3H-labelled phages was followed by a rapid breakdown of phage DNA, as demonstrated by the appearance of radioactive label in the cold-acid-soluble DNA fraction of extracted adsorption mixtures.