The genus Mycobacterium includes
many species that are commonly found in the environment
(in soil and water or associated with plants and animals),
as well as species that are responsible for two major human
diseases, tuberculosis (Mycobacterium tuberculosis)
and leprosy (Mycobacterium leprae). The distribution
of environmental mycobacteria was investigated in the context
of a long-term study of leprosy, tuberculosis, Mycobacterium
bovis BCG vaccination, and the responses of individuals
to various mycobacterial antigens in Karonga District, northern
Malawi, where epidemiological studies had indicated previously
that people may be exposed to different mycobacterial species
in the northern and southern parts of the district. A total
of 148 soil samples and 24 water samples were collected
from various locations and examined to determine the presence
of mycobacteria. The detection method involved semiselective
culturing and acid-fast staining, following decontamination
of samples to enrich mycobacteria and reduce the numbers
of other microorganisms, or PCR with primers specific for
the mycobacterial 16S rRNA gene, using DNA extracted directly
from soil and water samples. Mycobacteria were detected
in the majority of the samples, and subsequent sequence
analysis of PCR products amplified directly from soil DNA
indicated that most of the products were related to known
environmental mycobacteria. For both methods the rates of
recovery were consistently higher for dry season samples
than for wet season samples. All isolates cultured from
soil appeared to be strains of Mycobacterium fortuitum.
This study revealed a complex pattern for the environmental
mycobacterial flora but identified no clear differences
between the northern and southern parts of Karonga District.
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bio-degradation of wastes.
