Which organism pair is most characteristically associated with culture-negative infective endocarditis requiring special serology or PCR for diagnosis?

• A Streptococcus gallolyticus and Enterococcus faecalis
• B Coxiella burnetii and Bartonella species ✓
• C Staphylococcus lugdunensis and Streptococcus anginosus
• D Haemophilus aphrophilus and Actinobacillus actinomycetemcomitans

Explanation

Coxiella burnetii (Q fever) and Bartonella species are the leading causes of true culture-negative endocarditis and are diagnosed by serology (phase I IgG titre for Coxiella) or PCR. Option D lists HACEK organisms, which are fastidious but grow within 5 days in modern continuous-monitoring blood culture systems, so they are no longer classified as culture-negative. S. gallolyticus, enterococci and S. aureus all grow readily in routine cultures.

Reference: Harrison's Principles of Internal Medicine, 21st ed.

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