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 add-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. 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.
[1.] McCarter YS, Ratkiewicz IN, Robinson A. Cord formation in
BACTEC medium is a reliable, rapid method for presumptive identification
of Mycobacterium tuberculosis complex. J Clin Microbiol
[2.] Badak FZ, Goksel S, Sertoz R, Guzelant A, Kizirgil A, Bilgic
A. Cord formation in MB/BacT medium is a reliable criterion for
presumptive identification of Mycobacterium tuberculosis complex in
laboratories with high prevalence of M. tuberculosis. J Clin Microbiol.
[3.] Behling CA, Bennett B, Takayama K, Hunter RL. Development of a
trehalose 6,6'-dimycolate model which explains cord formation by
Mycobacterium tuberculosis. Infect Immunol. 1993;61:2296-2303.
Accepted for publication March 15, 2001.
From the Department of Pathology, Beth Israel Deaconess Medical
Center, Harvard Medical School, Boston, Mass.
Reprints: Liron Pantanowitz, MD, Department of Pathology, Beth
Israel Deaconess Medical Center, Harvard Medical School, 330 Brookline
Ave, Boston, MA 02215.