Infection caused by nontuberculous mycobacteria: clinical aspects

Identification of non-tuberculous mycobacteria: 16S rRNA gene sequence analysis vs. conventional methods

In a retrospective study, 45 clinical isolates of non-tuberculous mycobacteria were identified to the species level by biochemical profile, gas liquid chromatography and partial sequence analysis of 16S rRNA, and were found to represent 13 different species. The results of sequence analysis showed 100% identity with conventional tests for 34 isolates (76%) and could identify species such as M. bohemicum which are difficult to characterise with conventional methods. Most of the discrepant results for the remaining 11 isolates resulted in species of the same group of mycobacteria. Based on these findings. we concluded that direct sequence analysis of amplified 16S rRNA gene is a promising rapid and accurate method for species determination of non-tuberculous mycobacteria.

Rapidly growing mycobacterial lung infection in association with esophageal disorders

Esophageal or other swallowing disorders complicated by lipoid pneumonia are reported to be associated with pulmonary infections caused by rapidly growing mycobacteria. Herein we describe a 63-year-old woman with achalasia of the esophagus complicated by lung infection with Mycobacterium chelonae and a 47-year-old man in whom long-term ingestion of mineral oil was complicated by lipoid pneumonia and M. fortuitum lung infection. A MEDLINE search of English language publications from 1966 to 1997 revealed 18 cases of lung infections caused by rapidly growing mycobacteria in patients with esophageal disorders. Of these 18 patients and our 2 patients, 11 were men and 9 were women (mean age, 50 years). Achalasia was present in 11 patients, and 6 had lipoid pneumonia without evidence of esophageal disorders. Three patients had lipoid pneumonia caused by lipoid ingestion in the setting of achalasia or another swallowing disorder. In 14 patients, lung infection was caused by M. fortuitum; in 5, M. chelonae; and in 1, a non-M. fortuitum rapidly growing mycobacterial infection. The most common clinical feature was fever, and the most common roentgenologic abnormality was the presence of unilateral or bilateral and patchy or dense infiltrates. The sputum was the most common source of isolation of rapidly growing mycobacteria. Achalasia and lipoid pneumonia are important risk factors for the development of lung infections caused by rapidly growing mycobacteria. Treatment of the esophageal disease might prevent occurrence of and facilitate recovery from these infections.

PCR assay based on DNA coding for 16S rRNA for detection and identification of mycobacteria in clinical samples

A PCR and a reverse cross blot hybridization assay were developed for the detection and identification of mycobacteria in clinical samples. The PCR amplifies a part of the DNA coding for 16S rRNA with a set of primers that is specific for the genus Mycobacterium and that flanks species-specific sequences within the genes coding for 16S rRNA. The PCR product is analyzed in a reverse cross blot hybridization assay with probes specific for M. tuberculosis complex (pTub1), M. avium (pAvi3), M. intracellulare (pInt5 and pInt7), M. kansasii complex-M. scrofulaceum complex (pKan1), M. xenopi (pXen1), M. fortuitum (pFor1), M. smegmatis (pSme1), and Mycobacterium spp. (pMyc5a). The PCR assay can detect 10 fg of DNA, the equivalent of two mycobacteria. The specificities of the probes were tested with 108 mycobacterial strains (33 species) and 31 nonmycobacterial strains (of 17 genera). The probes pAvi3, pInt5, pInt7, pKan1, pXen1, and pMyc5a were specific. With probes pTub1, pFor1, and pSme1, slight cross hybridization occurred. However, the mycobacterial strains from which the cross-hybridizing PCR products were derived belonged to nonpathogenic or nonopportunistic species which do not occur in clinical samples. The test was used on 31 different clinical specimens obtained from patients suspected of having mycobacterial disease, including a patient with a double mycobacterial infection. The samples included sputum, bronchoalveolar lavage, tissue biopsy samples, cerebrospinal fluid, pus, peritoneal fluid, pleural fluid, and blood. The results of the PCR assay agreed with those of conventional identification methods or with clinical data, showing that the test can be used for the direct and rapid detection and identification of mycobacteria in clinical samples.