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Diagnostic challenges in detecting coagulase-negative Staphylococcus aureus by coagulase testing
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Background: Staphylococcus aureus is a major human pathogen whose identification in clinical laboratories often relies on the detection of coagulase activity. While rabbit plasma has long been considered the gold standard for the tube coagulase test, discrepancies in test results between plasma sources have been reported, raising concerns about diagnostic accuracy.
Methods: A total of 64 clinical isolates of S. aureus from human skin, along with the reference strain ATCC 25923, were tested for coagulase activity using human and rabbit plasma. Tube coagulase tests were performed at 4 and 24 hours, and slide coagulase tests were conducted in parallel. Positive results were defined by visible clot formation in the tube tests or clumping within 30 seconds in the slide tests.
Results: With human plasma, 32.8% of isolates were coagulase-positive at 4 hours, increasing to 51.6% after 24 hours. In contrast, only 4.7% of isolates tested positive with rabbit plasma at both 4 and 24 hours. Slide coagulase testing with human plasma demonstrated 100% positivity, whereas the same assay with rabbit plasma yielded only 10.9% positivity.
Conclusion: Coagulase detection in S. aureus is strongly influenced by the plasma source and incubation time. Sole reliance on rabbit plasma may result in significant underdiagnosis, particularly for human-adapted strains. Incorporating multiple plasma sources, extending incubation, and employing confirmatory methods can enhance diagnostic accuracy and prevent misclassification of coagulase-negative S. aureus.
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Từ khóa
Staphylococcus aureus, coagulase test, human plasma, rabbit plasma, diagnostic accuracy, false-negative
Tài liệu tham khảo
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