Performance and clinical significance of a direct tube coagulase test using serum separator tubes for rapid identification of Staphylococcus aureus from blood culture broth

D. Kwa, T. Schülin-Casonato, P. Sturm

Author address: 

Nijmegen, NL

Abstract: 

Objective: Blood cultures are important in the diagnosis of serious infections. Early administration of effective antibiotics is associated with improved patient outcome. The performance of the direct tube coagulase (DTC) using serum separator tubes (SSTs) for rapid identification of S. aureus from blood culture broth (BCB) was investigated. The clinical significance of rapid identification was assessed. Methods: Consecutive blood cultures with gram-positive cocci in clusters were tested. BCB was collected in SSTs using a subculture-venting unit. After centrifugation, the supernatant was discarded and 1 ml rabbit plasma was added to the remaining pellet of bacteria. Coagulation was evaluated after 2 and 4 hours incubation at 37°C, and after overnight incubation at room temperature. In parallel, a direct tube coagulase test was performed using a 1:10 saline dilution of BCB as described previously. Isolates were identified by standard microbiology procedures. Clinical significance was measured by comparison of antimicrobial prescription based on Gram stain results, direct coagulase results, and culture results. Results: Over a 6-week period, 90 BCBs from 46 patients were tested. S. aureus was present in 22 BCBs. Using the serum separator tube method and the saline dilution method, the sensitivity of the DTC after 2 hours incubation was 91% and 41%, and after 4 hours 100% and 88%, respectively. The specificity of both methods was 100%. Rapid identification of S. aureus resulted in initiation (n = 1) or streamlining (n = 4) of antimicrobial therapy in 5 of 13 patients with S. aureus bacteremia. Rapid identification of coagulase-negative staphylococci resulted in changes in antimicrobial therapy in 1 of 33 patients. Conclusion: The DTC using SSTs for bacterial enrichment is a very reliable, rapid, cheap and easy to perform method for identification of S. aureus from BCB. Implementation of this test can improve antimicrobial therapy.
2006

abstract No: 

P1720

Full conference title: 

16th European Congress of Clinical Microbiology and Infectious Diseases
    • ECCMID 16th (2006)