The Addition of Para-aminobenzoic Acid or Catalase to Löwenstein-Jensen Medium and the Effect of Prolonged Incubation in the Culture of Tubercle Bacilli

The culture of tubercle bacilli from sputum is one of the most important methods of assessing response in controlled trials of the chemotherapy of tuberculosis. If the method of culture employed in such trials fails to allow growth of any particular type of tubercle bacillus, for example those resistant to isoniazid, or is influenced by the chemotherapy given to a particular group of patients, such as those receiving PAS, serious bias can be introduced in the evaluation of the efficacy of the experimental regimens. In consequence, during the course of two controlled trials at the Tuberculosis Chemotherapy Centre, the method of culture on Löwenstein-Jensen medium was studied in comparison with culture on Löwenstein-Jensen medium to which PABA or catalase had been added, to see whether it was proving adequate both for culture of tubercle bacilli from patients receiving PAS and isoniazid, and also for culture of isoniazid-resistant tubercle bacilli from patients receiving either PAS and isoniazid, or isoniazid alone. In both these trials there was an appreciable incidence of smearpositive, culture-negative specimens, but evidence has been presented that it was justifiable to conclude that the bacilli in these specimens were non-viable (Tuberculosis Chemotherapy Centre 1959, 1960b). The method of culture employed differed from that of Fruhlinger and Bala (1953), Yegian, Budd and Bala (1955), and Duerr (1957) in that, after treatment with sodium hydroxide, the centrifuged deposit was washed with a large volume of water before addition to the culture medium. In addition to these investigations a sample of the cultures which were negative after 8-9 weeks were incubated for a further period of 8 weeks (a total of 16-l7 weeks incubation), to investigate whether any further positive cultures could be obtained, as has been suggested by Duerr (1957)