Abstract:
Background: Determination of the prevalence and drug susceptibility of the M. tuberculosis strains is important in
tuberculosis control. We determined the genetic diversity and susceptibility profiles of mycobacteria isolated from
tuberculosis patients in Mbarara, South Western Uganda.
Methods: We enrolled, consecutively; all newly diagnosed and previously treated smear-positive TB patients aged
≥ 18 years. The isolates were characterized using regions of difference (RD) analysis and spoligotyping. Drug
resistance against rifampicin and isoniazid were tested using the Genotype® MDRTBplus assay and the indirect
proportion method on Lowenstein-Jensen media. HIV-1 testing was performed using two rapid HIV tests.
Results: A total of 125 isolates from 167 TB suspects (60% males) with a mean age 33.7 years and HIV prevalence
of 67.9% (55/81) were analyzed. Majority (92.8%) were new cases while only 7.2% were retreatment cases. All the
125 isolates were identified as M. tuberculosis strict sense with the majority (92.8%) of the isolates being modern
strains while seven (7.2%) isolates were ancestral strains. Spoligotyping revealed 79 spoligotype patterns, with an
overall diversity of 63.2%. Sixty two (49.6%) of the isolates formed 16 clusters consisting of 2-15 isolates each.
A majority (59.2%) of the isolates belong to the Uganda genotype group of strains. The major shared spoligotypes
in our sample were SIT 135 (T2-Uganda) with 15 isolates and SIT 128 (T2) with 3 isolates. Sixty nine (87%) of the 79
patterns had not yet been defined in the SpolDB4.0.database. Resistance mutations to either RIF or INH were
detected in 6.4% of the isolates. Multidrug resistance, INH and RIF resistance was 1.6%, 3.2% and 4.8%, respectively.
The rpob gene mutations seen in the sample were D516V, S531L, H526Y H526D and D516V, while one strain had a
Δ1 mutation in the wild type probes. There were three strains with katG (codon 315) gene mutations only while
one strain showed the inhA promoter gene mutation.
Conclusion: The present study shows that the TB epidemic in Mbarara is caused by modern M. tuberculosis strains
mainly belonging to the Uganda genotype and anti-TB drug resistance rate in the region is low.
