Etiologic importance of coagulase-negative Micrococcaceae isolated from blood cultures

Coagulase-negative Micrococcaceae from blood cultures were classified biochemically according to Baird-Parker and to Kloos & Schleifer and by means of antibiotic susceptibility testing, in an attempt to distinguish between bacterial growth due to contamination and growth due to bacteremia. S. epidermidis biotype 1 (according to Baird-Parker) accounted for c. 60% of the isolates and for c. 85% of the isolates considered to be of clinical importance. The more time- and resource-demanding classification of Kloos & Schleifer provided no further clinically useful information, as the predominant number of isolates turned out to be S. epidermidis. Isolates other than S. epidermidis (according to Kloos & Schleifer) accounted for c. 45% of the total number of isolates but for only 20% of the isolates considered of clinical importance. Resistance to multiple antibiotics was recorded more often in isolates from patients with positive clinical information than in isolates thought to be contaminators. The frequency of blood cultures contaminated with coagulase-negative Micrococcaceae was estimated at c. 1.5%. Records from 91 patients were reviewed. By correlating the clinical findings to biochemical classification, resistance types, and the massiveness of growth it was suggested that the quantitative rather than the qualitative findings are suitable for determining clinical significance of isolates of coagulase-negative Micrococcaceae from blood cultures.