"Cord formation" in smear specimen prepared from sputum for a more rapid method of presumptive identification of Mycobacterium tuberculosis

Cord formation of Mycobacterium tuberculosis complex is very uncommon in smear specimen prepared directly from sputum, although such a finding is well known in solid or liquid media and has recently been evaluated as a rapid method for presumptive identification in special liquid media (BACTEC or MGIT). We examined 308 (Mycobacterium tuberculosis 271 and Nontuberculous mycobacteria 37) positive smear specimens prepared directly from sputum in our hospital. These specimens all showed a "modified Gaffky scale" as +2 or more and this cord formation was found in four cases (five specimens). Each of these specimens was from a patient with severe lung tuberculosis showing cavity formation and each patient was complicated severe diabetes mellitus. The morphology of cord formation on smear specimens prepared directly from sputum was similar to that in liquid or solid media, and consequently the relevant bacilli were identified as Mycobacterium tuberculosis complex by PCR examination. In this study, we assessed "cord formation" in smear specimen prepared directly from sputum as a more rapid presumptive identification of Mycobacterium tuberculosis complex based on microscopic morphology, as well as cord formation in liquid or solid media.