Journal of Clinical Pathology, 4, 183
- W., J. E. Southall
- Fisher, M. W.
One of the difficulties in the rapid laboratory diagnosis of tuberculosis is the time required for a satisfactory growth of the tubercle bacillus to appear on artificial medium. This delay is even more important when it is also desirable to determine the sensitivity of the organism. While in some cases it may not be of paramount importance to obtain a rapid growth of the tubercle bacillus for routine diagnosis, the result of the sensitivity test to be of any great value to the clinician must be available in the shortest possible time. Therefore, the ideal to be aimed at should be the rapid isolation of the organism and the simultaneous determination of its sensitivity. The medium used for isolating M. tuberculosis in many laboratories is that of LowensteinJensen. This medium is satisfactory, but growth of the organism is not usually obtained in less than 14 to 28 days. Slide culture in saponated blood (Giammalvo, Natsios, and Elton, 1949) is more rapid, but the method is too laborious and requires considerable skill. Tarshis and Frisch (1951a and b) and Frisch and Tarshis (1951) demonstrated the value of human blood in culturing the tubercle bacillus. For sensitivity determinations the serial dilution tube method (M.R.C. Report, 1948) has been widely used but again it is time consuming, and it is necessary to have a culture of the organism already growing. The slide culture method, although accurate, also takes too much time, and is potentially dangerous in a busy laboratory. The incorporation of antibiotic in solid medium is used but requires specially prepared medium and duplicates, both for control purposes and in testing a range of concentrations. The diffusion method of Tinne and Henderson (1950) is convenient but it is essential to keep the bottle upright during the whole period of the test. A more convenient reservoir of the antibiotic is the compressed tablet (Hoyt, 1951), the filter paper strip (Fairbrother and Southall, 1951), or the filter paper disc (Gould and Bowie, 1952). This paper describes a method whereby the isolation and sensitivity of the tubercle bacillus can be determined simultaneously by adopting the filter paper disc technique and a saponated human blood agar medium. This medium was suggested by Dr. W. M. Levinthal, of the Bacteriology Department, Astley Ainslie Institute, Edinburgh, and, after development by one of us, was found to give more rapid results than the Lowenstein-Jensen medium. Media Saponated Blood Agar.--To 95 ml. of citrated group 0 human blood, 5 ml. of 10% saponin is added, and the mixture heated to 550 for five minutes. Equal quantities of saponated blood and a 4% agar solution (not nutrient) are then mixed at 45'. If kept in the refrigerator this medium will remain suitable for 10 days. Lowenstein-Jensen Solid Medium (Mackie and McCartney, 1948).-This medium was sloped in 10 ml. amounts in 1 -oz. "universal " containers, the containers being held horizontal during solidification. Petri dishes containing 5-mm. thicknesses were also used. Dubos Fluid Medium (Dubos and Davis, 1946).This was kept in I-oz. containers.