Improved isolation of mycobacteria other than Mycobacterium tuberculosis on isoniazid-containing Löwenstein-Jensen medium

The early bactericidal activity of isoniazid related to its dose size in pulmonary tuberculosis

Collections of sputum from 105 patients with newly diagnosed pulmonary tuberculosis were made before and at 1 and 2 d after the start of chemotherapy with isoniazid (INH) alone given to groups of patients in doses of 600 mg, 300 mg, 150 mg, 75 mg, 37.5 mg, 18.75 mg, and 9 mg daily, as well as from an untreated group. Counts of colony forming units (cfu) of Mycobacterium tuberculosis in the collections were set up on plates of selective 7H10 medium. The early bactericidal activity (EBA) of INH was defined as the decrease in log10 cfu/ml sputum/day during the first 2 d of treatment. A smooth curve relating EBA to log dose was obtained, with 600 mg INH yielding the highest mean EBA of 0.539, and 18.75 mg INH yielding the lowest EBA (0.111) that could be distinguished from the bactericidal activity of the untreated group. The ratio of the usual dose of 300 mg INH to the lowest dose, of 18.75 mg, that produced a detectable EBA, termed the therapeutic margin, was therefore 16, in contrast to the lower therapeutic margin of 4 for rifampin. The EBA was related to the INH acetylator genotype of patients treated with 600 mg or 9 mg INH.

Detection of 2-eicosanol by gas chromatography-mass spectrometry in sputa from patients with pulmonary mycobacterial infections

A total of 96 sputum specimens from patients with suspected or known mycobacterial and nonmycobacterial pulmonary infections were analyzed by gas chromatography-mass spectrometry for the presence of 2-eicosanol. This secondary alcohol was detected in all of the 25 sputum specimens culture positive for Mycobacterium tuberculosis, in 7 of the 9 sputum specimens culture positive for M. avium complex, and in all 3 of the studied sputum specimens associated with M. malmoense. The alcohol was not detected in any of the 45 culture-negative sputum specimens or in 14 sputum specimens culture positive for Staphylococcus aureus, Pseudomonas aeruginosa, Haemophilus influenzae, and Streptococcus pneumoniae. The ratio of tuberculostearic acid to 2-eicosanol was much lower in sputum samples culture positive for mycobacteria than in the corresponding in vitro-grown cultures. The present findings indicate that 2-eicosanol may be useful as a chemical marker for rapid diagnosis of pulmonary infections caused by the M. avium complex, M. malmoense, and M. tuberculosis.

Bronchoscopic diagnosis of pulmonary infections in a heterogeneous, nonselected group of patients

Fiberoptic bronchoscopy with bronchoalveolar lavage and protected specimen brush technique has become an established method for etiologic diagnosis in severe forms of pulmonary infections during recent years. In this study, including 62 bronchoscopies in 53 patients, a standardized program, covering all important pulmonary pathogens, has been evaluated in a heterogeneous group of patients. Results providing therapeutic guidelines were obtained in 53 percent (16/30) of the immunocompromised patients (including 5 bronchoscopies on HIV-positive patients), but only 19 percent (6/32) of the immunocompetent patients (p < 0.001). We conclude that bronchoscopy is of great value for diagnosing pulmonary infections in immunocompromised patients. In immunocompetent patients, the diagnostic yield is lower and the indication for bronchoscopy must be established for each individual patient based on clinical importance, resources, and risk. When bronchoscopy is performed, we believe that a standardized program like ours reduces the risk of missing important pathogens.