Direct cord reading agar in routine mycobacteriology.

A group of 2,081 sputum specimens were planted on Direct Cord Reading Agar. A total of 330 (16%) of these specimens produced positive cultures, 312 strains of Mycobacterium tuberculosis and 18 strains of atypical mycobacteria. The strains of M. tuberculosis showed visible cords on plates in 283 (90.8%) of the isolates and no atypical mycobacteria showed cording. The specimens from the newly admitted patients yielded, in 12 days, 59% of their total positives; 97.6% of these strains, identified as M. tuberculosis with the standard methods recommended by the National Communicable Diseases Center, exhibited cording visible directly on the agar. It is suggested that, for practical purposes, a colony exhibiting cording could be tentatively reported as "M. tuberculosis to be confirmed."