Distribution of Environmental Mycobacteria in Karonga District, Northern Malawi

Abstract

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.

Mycobacteria in water, soil, plants and air: a review

“…The mycobacterial isolates from soil were identified as M. fortuitum, whereas the uncultured sequences obtained from soil DNA fell into a few closely related groups, either M. fortuitum or other fast-growing mycobacteria, like M. tokaiense, or M. austroafricanum and M. heidelbergense. However, the method described in this study based on the sequencing of a 473 bp region of the 16SrRNA gene, cannot be used to discriminate many species that are human and animal pathogens, i.e., M. tuberculosis, M. avium, M. bovis and M. leprae, although sequences belonging to this group were identified (Chilima et al 2006;Lavania et al 2008;Turankar et al 2012).…”

Prevalence of Mycobacterium leprae in the environment: A review

“…This result might be closely linked to climatic changes in the environment, as the bacilli can be removed from the soil and reducing the density of these bacterial population owing to the presence of the excess rainwater. The challenge in the study was the variety of mycobacteria in the soil, which might indirectly influence human health (Chilima et al, 2006). The incidence of leprosy was three times higher in the northern part of the district, which is warmer and more humid than the southern (Fine et al, 1994).…”

Real vaccines in the real world: tuberculosis vaccines move south

“…There are many of them -some more exotic than others -and most do not cause disease except in the immunocompromised [6]. Some are found in soil, others in water -with a limited number of studies performed in Africa [7,8]. Some are probably impossible to cultivate and completely undocumented.…”