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.
We evaluated cord formation in MB/BacT broth as a rapid method for presumptive identification of the Mycobacterium tuberculosis complex. Kinyoun acid-fast-stained smears from 370 positive MB/BacT bottles were examined for the presence of serpentine cording. The smears were examined independently by two observers. Observer 1 (the supervisor of the mycobacteriology laboratory) examined all of the smears while observer 2 (a clinical microbiologist not familiar with acid-fast bacillus [AFB] microscopy) examined 148 randomly chosen smears that were read by observer 1 without knowledge of which smear was which. The sensitivity, specificity, and positive and negative predictive values of cording for the presumptive identification of M. tuberculosis read by observer 1 were 88.2, 97.4, 99.2, and 69.7%, respectively. These values were reported at 90.6, 52.3, 82.8, and 69. 7%, respectively, by observer 2. Our laboratory prevalence of M. tuberculosis among positive cultures was 78% during the time this study was conducted. At the time of positive signal of the MB/BacT bottles, the broth of the bottles had sufficient cell mass to allow for observation of the presence or absence of serpentine cording. The presence of cords in MB/BacT broth is a reliable criterion for rapid, predictive identification of the M. tuberculosis complex for laboratories with a high proportion of the M. tuberculosis complex when the smears are examined by a microbiologist who has experience with AFB staining.
Badak
F Z
FZ
Department of Clinical Microbiology, Ege University Medical School, Izmir, Turkey. zarinc@juno.com
Goksel
S
S
Sertoz
R
R
Guzelant
A
A
Kizirgil
A
A
Bilgic
A
A
D015373:Bacterial Typing Techniques; D003311:Cord Factors / Q000378:metabolism*; D003470:Culture Media; D006801:Humans; D007753:Laboratories; D009169:Mycobacterium tuberculosis / Q000145:classification* / Q000254:growth & development* / Q000378:metabolism; D011237:Predictive Value of Tests; D012137:Respiratory System / Q000382:microbiology; D012680:Sensitivity and Specificity; D014376:Tuberculosis / Q000382:microbiology*
D003311:Cord Factors; D003470:Culture Media