Observation on the bacteriophage typing of mycobacterium tuberculosis isolates from the socialist people's Libyan Arab Jamahiria

Strains of Mycobacterium tuberculosis isolated from Libyan patients suffering from pulmonary tuberculosis were studied to determine strain variation. Susceptibility to mycobacteriophages was chosen as the principal method. Strains of mycobacteria were collected from a Libyan population in two batches at an extended interval, isolates from the first batch being made in 1976-77 and the second batch in 1979. Several bacteriophage types were recognised in each batch. The first group of isolates consisted principally of Type A strains of M.tuberculosis with only a few strains of Type B or Type Intermediate (I). The second batch, though showing high susceptibility to bacteriophage Type A (53% of isolates) also showed quite a high percentage to Type B (21%) and Type I (25.8%). A considerable change in bacteriophage susceptibility between the strains of the first and second batch was therefore demonstrated. The change was clear-cut in Tripoli, Zawia and Tarhuna, where both Type B and I increased. No correlation was observed between in-vitro drug resistance of the strains of bacteriophage types. Strain resistance to isoniazid was observed amongst all three bacteriophage types. No correlation -2-was demonstrable between the strains isolated from new and previously-diagnosed cases. A small study of M.tuberculosis strains isolated from patients in the expatriate group in the region under study revealed that bacteriophage Type A and I strains predominate among Algerians, Tunisians and Chadians, while Type I is the commonest among strains from Sudanese and Pakistani expatriates. Seventy-five per cent of the strains isolated from Egyptain expatriates were found to be susceptible to the bacteriophages lytic for Type B strains. It is concluded that bacteriophage Type B is rare in most of North Africa, with the exception of Egypt, while Type A is the most common.The increase of pulmonary tuberculosis among expatriates is suggested as a possible factor in the exchange of M.tuberculosis strains between the local population and the expatriate groups. This exchange hypothesis, formulated on the basis of the frequency c of different bacteriophage types, is discussed.