The use of monoclonal antibodies to identify mycobacteria grown in culture in Zimbabwe

Abstract

Monoclonal antibodies (Mabs) were used in an ELISA system to identify 462 mycobacterial isolates from clinical specimens in Zimbabwe. Cultures of mycobacteria were either sonicated or mechanically homogenised and used to coat the wells of microtitre plates. The mouse Mabs used reacted to lipoarabinomannan, an antigen common to all species of mycobacteria, to a 16 kDa protein specific to members of the Mycobacterium tuberculosis complex, to a glycolipid found in the cell wall of M. kanasii and to a glycolipid found in the cell wall of members of the M. avium-intracellulare complex. On the basis of serologic reactivity 443/462 (94%) isolates were identified as M. tuberculosis, 6/462 (1%) were identified as M. avium-intracellulare and 7/462 (2%) were identified as M. kansasii. The remaining 16 isolates gave negative reactions with each of the monoclonals, except that reactive with lipoarabinomannan. On the basis of biological tests on the 13 of the isolates that were available, 6 were identified as M. tuberculosis and 3 as M. bovis. In each of these the optical densities in the ELISA with at least one of the Mabs directed against the 16 kDa protein, was within 0.2 units of the cut off value. 4 isolates were not identifiable using biological tests in our laboratory. Each of the available isolates identified serologically as M. avium-intracellulare or M. kansasii gave biological reactions consistent with this identification. This study has shown Mab-ELISA to be a reliable means of rapidly identifying large numbers of mycobacterial isolates in a reference laboratory in Zimbabwe. It is noteworthy that despite the high prevalence of HIV in tuberculosis patients in Zimbabwe, very few were infected with atypical mycobacteria.