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Applied and Environmental Microbiology, April 2006, p. 2343-2350, Vol. 72, No. 4
0099-2240/06/$08.00+0     doi:10.1128/AEM.72.4.2343-2350.2006
Copyright © 2006, American Society for Microbiology. All Rights Reserved.

Distribution of Environmental Mycobacteria in Karonga District, Northern Malawi

Benson Z. Chilima,1,2,{dagger} Ian M. Clark,1 Sian Floyd,2 Paul E. M. Fine,2 and Penny R. Hirsch1*

Rothamsted Research, Harpenden, Hertfordshire AL5 2JQ, United Kingdom,1 London School of Hygiene and Tropical Medicine, London WC1E 7HT, United Kingdom2

Received 28 September 2005/ Accepted 13 January 2006

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.

* Corresponding author. Mailing address: Plant Pathogen Interactions Division, Rothamsted Research, Harpenden, Hertfordshire AL5 2JQ, United Kingdom. Phone: (44) (0) 1582 763133. Fax: (44) (0) 1582 760981. E-mail: penny.hirsch{at}bbsrc.ac.uk.

{dagger} Present address: National Public Health Reference Laboratory, Community Health Sciences Unit, Private Bag 65, Lilongwe, Malawi.

Applied and Environmental Microbiology, April 2006, p. 2343-2350, Vol. 72, No. 4
0099-2240/06/$08.00+0     doi:10.1128/AEM.72.4.2343-2350.2006
Copyright © 2006, American Society for Microbiology. All Rights Reserved.



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