Biotyping of coagulase-negative staphylococci. 108 isolates from nosocomial bloodstream infections.

Using simple, readily available typing methods, we evaluated 108 strains of coagulase-negative staphylococci that were causally related to bloodstream infections: 95% (103 of 108) of the isolates were identified as Staphylococcus epidermidis and were divided into 18 biotypes by API Staph-Trac. A single biotype (biotype A, 6606113) accounted for greater than 50% of the isolates of S. epidermidis. Biotype A was further divided into seven subtypes by slime production and synergistic hemolysis; however, 66% of the isolates in biotype A remained in two major subtypes, 1a (strongly slime-positive and synergistic hemolysis-positive) and 2a (strongly slime-positive and synergistic hemolysis-negative). The addition of the antibiotype further separated the isolates into individual strains or into small groups of organisms. A significant correlation was noted between synergistic hemolysis and the three most resistant antibiotypes (p = 4.2 X 10(-5); OR = 5.8; CI95, 2.2-15.2). Each biotype, subtype, and antibiotype was further divided into multiple unique strains by plasmid pattern analysis. In most clinical situations the combination of API Staph-Trac, antibiotic profile, slime production, and synergistic hemolysis provides adequate strain discrimination. Plasmid pattern analysis adds important information in specific clinical situations and may be invaluable for epidemiologic investigations.