High Mycobacterium bovis genetic diversity in a low prevalence setting

The genetic diversity among South African Mycobacterium bovis isolates from cattle was determined by genetic fingerprinting. The restriction fragment length polymorphism (RFLP) markers IS6110 and polymorphic GC-rich sequence (PGRS) as well as spoligotyping and determination of variable number of tandem repeats (VNTR) were used to characterize sub samples of 91 M. bovis field isolates. PGRS RFLP was the single most discriminatory method and combinations of typing methods, which included IS6110 and/or PGRS had the highest discriminatory power, able to reveal 29 distinct genotypes among 35 farms with no epidemiological link. Three of the farms were co-infected with two genetically unrelated strains. In contrast to reports from European and also other colonised countries on the African continent our findings are suggestive of a high genetic diversity of M. bovis in South Africa's cattle population, implying a variety of unrelated ancestor strains. Despite effective intervention through test-and-slaughter campaigns no indication of a 'founder effect' was apparent in the panel of isolates derived from all infected provinces.