Molecular characterization of isolates from pulmonary tuberculosis patients in Khartoum, Sudan.

BACKGROUND

The aim of this study was to characterize the drug resistance profile, and the specific lineages of Mycobacterium tuberculosis (MTB) strains isolated from patients with pulmonary TB in the state of Khartoum in Sudan.

METHODS

Consecutive sputum samples and clinical data were collected from 406 smear-positive TB patients with pulmonary TB in 2007-2009. The samples were cultured, and drug susceptibility testing (DST) was performed using the proportion method (PM) on solid Löwenstein-Jensen medium, and species were identified using biochemical methods at the National Reference Laboratory (NRL) in Khartoum. Extracted deoxyribonucleic acid from a total of 120, 60 suspected multidrug-resistant isolates (MDR), and 60 non-MDR isolates were subsequently sent to the WHO supranational reference laboratory (SRL) in Stockholm at the Public Health Agency of Sweden, for confirmation of the drug resistance profile, examinations by line probe assay (LPA), and molecular epidemiology analysis with Spoligotyping.

RESULTS

LPA results correlated 100% for non-MDR and 62% for the suspected MDR strains when compared to the DST results obtained by PM at the NRL. Two strains were initially using the PM identified as MDR-TB but later shown by Hain GenoType Mycobacterium CM/AS to belong Mycobacterium avium complex (Mycobacterium intracelluare). These two strains were excluded from the study material for further analysis. The remaining 58 MDR strains were analyzed using LPA, and 36 strains were confirmed as MDR, 10 as rifampicin monoresistant, and eight as isoniazid-monoresistant. Spoligotyping for all the 118 MTB isolates revealed a total of 115 patterns in which four patterns represented major clusters with a total of 108 (91%) of the strains. The CAS1_Delhi/family was the predominant type and detected in 62 isolates (52%), of which 26 were MDR and 36 were susceptible. It was followed by H3/family with 19 (16%) strains, and 11 Latin American Mediterranean3/family, 16 T2/T1, and two strains each of the Beijing and S lineage.

CONCLUSION

Comparison of DST results obtained using PM and LPA showed 100% agreement for the non-MDR strains but only 62% for the MDR strains. Taking in consideration the time, risk of contamination and the cost of labour to identify MDR TB, the LPA have clear advantages in early detection of MDRTB than the PM. Additionally in this study material Spoligotyping revealed the CAS1 Delhi as the most predominant family. We could not see no major difference in lineages between MDR and non-MDR strains.