Photometry of Mycobacteria and its application in sensitivity-testing of chemotherapeutic agents (author's transl)

Using photometry in measuring the growth of mycobacteria in liquid medium 7 H 9 Middlebrook slightly modified, we could achieve a 5 to 8 fold increase of extinction values within 8 days. The reproducibility of these results were investigated by tenfold assay of the laboratory mycobacterial strain H37Rv and about 10 strains recently isolated from patients. As antituberculous chemotherapeutic agents require different pH for their optimal activity, the experiments were performed at pH 5.5, pH 6.8 and pH 7.3. By daily measuring the extinction values of all strains showed less growth at pH 5.5 compared to their behaviour at pH 6.8 and 7.3. Yet growth at pH 5.5 was sufficient to estimate the inhibitory effect of Pyrazinamide as later experiments could show. The variation coefficient at pH 5.5 revealed to be significantly lower than at pH 6.8 and pH 7.3. Isoniazid, Prothionamid and Rifampicin were tested at pH 6.8, Streptomycin, Ethambutol and Tetracyclin at pH 7.3 and Pyrazinamide at pH 5.5. The results of our calculations were expressed as growth percentages in relation to growth in the control tubes. Usüally the measurements of the last day of incubation were chosen for this evaluation. Inhibition of growth in 50% or more of the extinction values of the control tubes was the criterion for regarding a strain as sensitive to a given drug. All drugs were tested in two concentrations. In case of only one concentration effecting inhibition of growth in 50% ore more, the strain was reported to give a borderline result. Sensitivity testing with photometry was compared to conventionally performed tests on Loewenstein-Jensen-Medium which were in good agreement between 80 and 100%. Results being available within 8 days in an advantage of the photometric method of sensitivity testing. Furthermore Pyrazinamide and Tetracyclin can be tested without difficulties while these drugs give unsatisfactory results when tested on Loewenstein-Jensen-medium.