ABSTRACT
This study included 163 tuberculous patients and 43 persons of their healthy contacts. Seventy one strains of mycobacteria were isolated from sputum and only one strain from urine samples. Out of these; 46 strains have been identified as M. tuberculosis and 11 strains as M. bovis based on the results of niacin production, nitrate reduction and TCH susceptibility tests. Ten strains of M. tuberculosis were subjected to the invivo virulence assay of Mitchison. All tested strains were found to be highly virulent. Thus the prevalence of south Indian or low virulent variants of M. tuberculosis in Egypt is not a possibility. The results of tuberculin testing with PPD-B, in the patients and contacts under study, showed a very low prevalence of sensitization to environmental mycobacteria [26. 9% among patients and 27. 9% among contacts]. Accordingly. these findings suggest that the two hypotheses proposed to be among the important causes of failure of protective effect of BCG in the south Indian trial are not present in the Egyptian population sample studied