Mycobacterium intracellulare among TB suspected patients in Bulgaria - microbiological aspects

Nontuberculous mycobacteria (NTM) are representatives of the genus Mycobacterium with a worldwide distribution, associated mainly with water, soil, and biofilms. Some of NTMs, such as Mycobacterium avium complex (MAC), are etiological agents of human diseases - disseminated or with different localization, most often pulmonary.

In the present study, we analyzed Mycobacterium intracellulare isolates recovered from clinical specimens of tuberculosis (TB) suspected patients in Bulgaria, 2018-2020.

The cultures were grown on solid and liquid media. For species identification, we used immune chromatographic (TB Ag MPT64) test and Line Probe Assay (LPA) from the positive cultures.

M. intracellulare was identified in 32 patients from 82,780 specimens. It was predominantly isolated in females - 62.5% vs. 37.5% in males. The most affected age group was 65 years and over (38%). The distribution of the isolates in Bulgaria was uneven. Most of them (65.6%) were concentrated in two districts of the country: Plovdiv and Sofia-city. All strains were sensitive to macrolides and aminoglycosides except one with macrolide resistance. NTM pulmonary disease was confirmed in 16 patients with M. intracellulare isolate.

Analysing the 32 M. intracellulare isolates identified among TB suspected patients in Bulgaria between 2018 and 2020, we found that only half of them met the American Thoracic Society (ATS) diagnostic criteria for NTM pulmonary disease. For the remaining patients with M. intracellulare isolates we did not have sufficient data to support this diagnosis. Efforts by Bulgarian respiratory and microbiological societies are needed for adherence to the international guidelines.