Tuberculosis (TB) remains a deadly infectious disease affecting millions of people worldwide; 95% of TB cases,
with 98% of death occur in developing countries. The situation in South Africa merits special attention.
A total of 21,913 sputum specimens of suspected TB patients from three provinces of South Africa routinely
submitted to the TB laboratory of Dr. George Mukhari (DGM) Hospital were assayed for Mycobacterium tuberculosis
(MTB) growth and antibiotic susceptibility. The genetic diversity of 338 resistant strains were also
studied. DNA isolated from the strains were restricted with Pvu II, transferred on to a nylon membrane and
hybridized with a PCR-amplified horseradish peroxidase 245 bp IS6110 probe. Of the 338 resistant strains,
2.09% had less than 5 bands of IS6110, and 98% had 5 or more bands. Unique restriction fragment length
polymorphism (RFLP) patterns were observed in 84.3% of the strains, showing their epidemiological independence,
and 15.7% were grouped into 22 clusters. Thirty-two strains (61.5%) from the 52 that clustered
were from Mpumalanga, 16/52 (30.8%) from Gauteng, and 4/52 (9.6%) from Limpopo province. Clustering
was not associated with age. However, strains from male patients in Mpumalanga were more likely to be
clustered than strains from male patients in Limpopo and/or Gauteng province. The minimum estimate for
the proportion of resistant TB that was due to transmission is 9.06% (52-22=30/331). Our results indicate
that transmission of drug-resistant strains may contribute substantially to the emergence of drug-resistant
tuberculosis in South Africa.