Acid-Fast Serpentine Cords of Mycobacterium tuberculosis

A 25-year-old man with a 2-month history of weight loss and night sweats complained of recent-onset left thigh pain and hyperesthesia. Radiologic investigation identified a large abscess within his left psoas muscle that extended from the left renal vein to the inguinal region. A smaller fluid collection was also noted within the right psoas muscle. These lesions were accompanied by bony destruction and sequestration of the fourth lumbar vertebra. Purulent fluid was drained from the left abscess, from which oxacillin-sensitive Staphylococcus aureus was isolated. The patient was treated with oxacillin, continuous pigtail drainage of the abscesses, and local debridement. Two weeks later, mycobacteria were recovered in culture from involved vertebral tissue. A Kinyoun-stained smear prepared from the BACTEC MGIT broth culture revealed serpentine cords (Figure 1). These ropelike aggregates consisted of numerous acid-fast bacilli (Figure 2). DNA hybridization studies definitively identified these bacteria as being Mycobacterium tuberculosis complex. Cord formation in liquid media and fluid samples is a reliable and predictive marker for M tuberculosis, whereas nontuberculous mycobacteria tend to orient randomly.1,2 The cord factor (trehalose 6,6′-dimycolate) responsible for this morphological phenomenon contributes significantly to the virulence of M tuberculosis.3 These toxic surface glycolipids evoke cytokine-related host weight loss and play a fundamental role in the genesis and persistence of granulomas. The cord factor also inhibits phagocytosis and hinders phagosome-lysosome fusion within activated host macrophages.