Development of a Bacteriophage-typing Set for Staphylococcus Epidermidis

Six phages isolated from lysogenic cultures of Staphylococcus epidermidis were used to type cultures in our collection classified previously as "untypable" with our original typing set of 13 phages, new clinical isolates from Missouri, and clinical isolates from Connecticut, Georgia, Pennsylvania, and Virginia. Typability with the new set of 6 phages and with our 13 original phages was compared. For 203 cultures, 81 (39.9%) cultures were typable with the set of 6 phages and 73 (36.0%) cultures were typable with the set of 13 phages. When the two typing sets were combined, the percentage of typability for 425 cultures increased to 49.9%. compared with 35.7% with the original set of 13 phages. For 109 cultures from outstate, the percentage of typability was 56.9%, whereas that for 316 cultures from Missouri was 47.5%. When only cultures in biotype 1 were considered, the percentage of typability for 268 cultures with the combined set increased to 58.2%, compared with 39.5% with the original set of 13 phages. Analysis of individual reactions for all 425 cultures typed in our laboratory indicated that 11 of the 19 phages in the combined set accounted for the majority of the reactions, and a provisional set containing these 11 phages is proposed.