Molecular characterization of Mycobacterium tuberculosis complex in Gambella region, Southwest Ethiopia

The information on the genetic diversity of Mycobacterium tuberculosis in certain geographic region is needed for a better understanding of epidemiology of TB and could have implications for development of new diagnostics, drugs, and vaccines. The aim of this study was to provide information on the strains of M. tuberculosis circulating in Gambella region. Cross-sectional study was conducted for six months (November 2012 and April, 2013) in order to generate a primary data on the genetic diversity of M. tuberculosis. Clinical examination, Ziehl Neelsen staining, Mycobacterium culturing and molecular typing were used. M. tuberculosis isolates were characterized using region of difference 9 (RD9) and spoligotyping. The patterns of strains identified by spoligotyping were compared with the patterns registered in the SpoIDB4 database of the Pasteur Institute. Culture positivity was confirmed in 53.49 % (46/86) of the smear positive cases. Upon molecular characterization, 86.95% (40/46) of culture positive samples were M. tuberculosis. The spoligotyping of the 40 isolates lead to the identification of 24 spoligotype patterns. Seven of the patterns were clustered and consisted of 2-3 isolates while the remaining 17 patterns were non-clustered consisting of a single isolate. The most prevalent strain was Spoligotyping International Typing (SIT) 289 with a proportion of 20.0% (8/40). Grouping of the isolates into lineages showed that 32.50% (13/40) were Euro-American, 17.50% (7/40) Indo-Oceanic, and amazingly the remaining 50.0% (20/40) of the isolates could not be grouped into the already known lineages and hence they were new. Findings from this study show that most of strains of M. tuberculosis circulating in the region are different from those reported from the other areas of the country. Hence, TB control program should give attention to the control of TB in Gambella region. In addition, characterizing the strains of M. tuberculosis circulating in the region would play a great role towards the mapping of molecular epidemiology of TB in Ethiopia.