Performance of phenotypic and genotypic methods to determine the clinical relevance of serial blood isolates of Staphylococcus epidermidis in patients with septicemia

Five typing methods, including biotyping (API ID32; BioMerieux, Marcy l'Eto ile, France), quantitative antibiogram typing based on actual zone sizes, p lasmid typing, randomly amplified polymorphic DNA (RAPD) analysis (with pri mer M13 and primer set ERIC-2-1026), and pulsed-field gel electrophoresis ( PFGE), were compared with a previously performed method of DNA fingerprinti ng by AFLP (amplified fragment length polymorphism analysis) for their perf ormance in the typing of blood isolates of Stapylococcus epidermidis. Sixte en epidemiologically unrelated strains and 11 sets of four blood culture is olates from 11 patients with septicemia were used. The stabilities and repr oducibilities of the patterns, the discriminatory capacities of the methods , and the ability to apply the methods to blood culture isolates were used as performance criteria. All strains tested were typeable by each method, a nd the patterns were stable and reproducible. The numbers of different type s within the collection of 16 epidemiologically different isolates were 5 b y biotyping, 14 by antibiogram typing, 4 by plasmid typing, 9 by the RAPD a ssay (combination of results with primer M13 and primer set ERIC-2-1026), a nd 16 by PFGE, Within the 11 sets of four blood culture isolates the types found by quantitative antibiogram typing! plasmid typing, and PFGE were uni que for each set, whereas by biotyping and RAPD analysis some types were ob served in more than one set. The results of biotyping did not correspond wi th the results of the other methods or the results of AFLP. For 6 of the 11 sets, the results of all methods except those of biotyping corresponded co mpletely. Quantitative antibiogram typing, PFGE, and AFLP proved to be the most accurate of the six typing methods tested.