Abstract:
Sub-Saharan Africa accounted for about 28% of the estimated 9.6 million of all notified tuberculosis (TB) cases in 2014. Due to high incidence of TB caused by Mycobacterium tuberculosis complex (MTBC) in developing countries, TB control activities have centered on MTBC to the neglect of non-tuberculous mycobacterial (NTM) infections. MTBC and NTM infections differ clinically, however, microscopy which is the mainstay of TB diagnosis in Ghana cannot distinguish between them. The inability to characterize acid fast bacilli (AFB) has led to improper treatment resulting in susceptible MTBC strains having an increased risk of developing resistance to first-line anti-TB drugs. In Ghana, very few studies have reported on the incidence and prevalence of TB due to specific MTBC species and their drug susceptibility test (DST) to first-line anti-TB drugs in Ghana. However, these studies did not have nationwide coverage. On the other hand, there is lack of national data on the species of NTM causing pulmonary infections as well as their DST patterns. This study sought to use World Health Organization (WHO) approved line probe assay (LPA) to differentiate MTBC and NTM isolates obtained from population-based TB prevalence survey in Ghana and to determine their DST patterns to isoniazid (INH) and rifampicin (RIF); and macrolides and aminoglycosides, respectively.
A retrospective study was conducted whereby a total of 361 mycobacterial isolates were differentiated and their drug susceptibility patterns determined using GenoType Mycobacterium Assays: MTBC and CM/AS for differentiating MTBC and NTM as well MTBDRplus and NTM-DR for DST patterns of MTBC and NTM, respectively.
All the isolates were obtained from sputum of participants aged between 15-100 years comprising 159 males and 202 females. Out of 361 isolates, 165 (45.7%) were MTBC
while 196 (54.3%) were NTM. The MTBC comprised 161 (97.6 %) Mycobacterium tuberculosis and 4 (2.4%) Mycobacterium africanum. Eighteen (10.9%) and 2 (1.2%) of the MTBC isolates were INH and RIF monoresistant respectively while 11 (6.7%) were multi-drug resistant (MDR). RIF resistance was associated with D516V (46.7%), H526Y (23.1%) and S531L (15.4%) mutations in rpoB whiles INH resistance was frequently associated with S315T (82.8%) mutation in katG. Mutations in the promoter region of inhA (34.4%) also resulted in isoniazid resistance. Fourteen different NTM species were identified, majority (21.4%) being M. fortuitum. NTM-DR enabled the DST of thirty six NTM isolates belonging to the M. avium complex and M. abscessus complex. These isolates were all susceptible to macrolides (clarithromycin, azithromycin) and aminoglycosides (kanamycin, amikacin, and gentamicin).
In conclusion, M. tuberculosis is still the dominant species causing TB in Ghana whiles M. fortuitum is the most frequently isolated NTM species from sputum. Also, resistance to isoniazid is high compared to rifampicin. The study showed the usefulness of the GenoType Mycobacteria assay series as appropriate tools for simple and rapid differentiation and DST of mycobacterial isolates to enhance adequate and prompt treatment of mycobacterial infections in Ghana.