Comparison of MGIT and Myco/F Lytic Liquid-Based Blood Culture Systems for Recovery of Mycobacterium tuberculosis from Pleural Fluid

Abstract

Tuberculosis (TB) is the most frequent cause of exudative pleural effusions in areas of high TB incidence. Studies have shown that Mycobacterium tuberculosis is the causative agent in up to 44% of HIV-seronegative people hospitalized with a pleural effusion (1–3), and the percentage is higher in HIV-seropositive people (4). Pleural TB is a paucibacillary disease. The pathogenesis of a tuberculous pleural effusion is likely due to a delayed hypersensitivity reaction to M. tuberculosis proteins (for a review, see reference 5) and not to a large burden of organisms. The scarcity of organisms makes it difficult to isolate M. tuberculosis from pleural fluid samples, leading to low rates of culture confirmation. Rich culture media are generally more sensitive in detecting M. tuberculosis in sputum and other clinical samples (6). Few studies have compared different liquid media and examined their potential role in combination with solid media for the diagnosis of tuberculous pleurisy. In this study, we compared the Bactec 9120 Myco/F lytic blood culture system (Myco/F lytic) to the Bactec mycobacterial growth indicator tube (MGIT) 960 system (Becton Dickinson, Sparks, MD) (with each liquid system used in conjunction with locally prepared Middlebrook 7H11 solid medium) with respect to time to positivity (TTP), sensitivity, specificity, and percent culture yield of M. tuberculosis isolates from pleural fluid.