S. Attorri et al., Assessment of morphology for rapid presumptive identification of Mycobacterium tuberculosis and Mycobacterium kansasii, J CLIN MICR, 38(4), 2000, pp. 1426-1429
Mycobacterium tuberculosis often exhibits serpentine cording when grown in
liquid medium, whereas Mycobacterium kansasii can be larger and cross-barre
d, We assessed the use of these morphologic characteristics as a cost-effec
tive method for rapid presumptive identification of isolates from BACTEC bo
ttles. Without specific training, using the Kinyoun acid-fast stain, defini
tive cording was found in 237 of 373 specimens positive for M. tuberculosis
(64%) and cross-barring was recognized within 63 of 76 (83%) of the specim
ens positive for M. kansasii, giving sensitivities specificities, positive
predictive values, and negative predictive values of 63.5, 96, 92, and 79%,
respectively, for M. tuberculosis and 83, 95, 59, and 98%, respectively, f
or M kansasii. With training and experience, these results improved to 74.5
, 98, 96, and 84% and 93, 98, 79, and 98%, respectively. The major improvem
ents were in distinguishing the pseudocording or loose aggregation of Mycob
acterium avium complex from M. tubereculosis and the long bended forms of M
ycobacterium gordonae from M. kansasii. Mycobacterium asiaticum and Mycobac
terium szulgai, which rarely occur, are genetically related to M kansasii a
nd morphologically difficult to distinguish. In defined circumstances, serp
entine cording and cross-barring can be used for rapid presumptive identifi
cation of M. tuberculosis and M. kansasii, respectively, and as guides for
initial probe selection to reduce costs.