Effect of storage for three months at different temperatures on the sensitivity to streptomycin and isoniazid of cultures of tubercle bacilli.
Devaki, V.; Mohan, K.; Gangadharam, P.R.J.
Indian Journal of Medical Research; 1967; 55; 1150-1158.
Maintenance of bacterial strains by repeated subcultivation is both, expensive, laborious and time-consuming; moreover, there is always the possibility of contamination or of differential selection of sub-strains with specific properties. In consequence, several methods, such as freeze-drying or storage at low temperatures, have been introduced by which bacterial cultures can be kept alive for long periods with their reproductive and metabolic activity at an extremely low level. However, information is rather sparse on such methods for the storage of tubercle bacilli. For instance, Corper and Gauss (1923) found that tubercle bacilli remained viable in Petroff's egg medium or glycerol agar after storage in the incubator or refrigerator for 4 to 8 months. Later workers (Heckly, 1950; Stern and Tompsett, 1951; Jones, 1957; Tsukamura, 1965) suggested preservation of cultures by freezing them in various diluents. More recently, Tarshis (1961) compared storage of cultures in various diluents at - 20°C and concluded that, with minor exceptions, most types of mycobacteria (including tubercle bacilli) can be stored for at least 3 years without any major change in their viability or drug resistance. However, these procedures are time-consuming, expensive and require special equipment and are, therefore, not very practicable in developing countries with limited resources.
Our attention was drawn to this problem of storage of cultures during the course of the first drug resistance survey undertaken by the Indian Council of Medical Research (in preparation). In this survey, the Central Laboratory at Madras had to undertake bacteriological examinations, including drug sensitivity tests, on a total of 2700 specimens of sputum sent from each of the 9 centres distributed in various parts of India. Sensitivity tests were set up on nearly all the positive cultures within 2 or 3 days of their becoming positive. However, the organizational problems encountered were considerable and often acute. This experience prompted the present investigation on the effect of storage at different temperatures on the viability and sensitivity to streptomycin and isoniazid of cultures of tubercle bacilli. The period of storage was chosen to be 3 months as this represents, in our opinion, a reasonable period in which an equitable distribution of the work-load can be arranged in any large-sized laboratory.
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