Effect of carbon dioxide on the primary isolation of Mycobacteria

Chauhan, M.M.; Sreenivas, T.R. and Chaudhuri, K. (1991) Effect of carbon dioxide on the primary isolation of Mycobacteria. Indian Journal of Tuberculosis, 38 (2). pp. 81-85.

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Abstract

To study the effect of carbon dioxide on the primary isolation of mycobacteria, 1005 clinical specimens were inoculated on Lowenstein Jensen’s medium and incubated in an atmosphere with or without additional 10% carbon dioxide. Of the total positive cultures, 30.8% grew only under 10% carbon dioxide and in 58.3% growth was first seen in that atmosphere. Of the positive cultures by either method, 13.4% were positive during the first week when grown with 10% carbon dioxide. Of the culture positives, 21.4% and 15.1% were obtained with 10% carbon dioxide incubation and without additional carbon dioxide respectively. The results of this study show that (1) 10% carbon dioxide increases the yield of mycobacteria in primary culture, (2) it stimulates the temporal growth rate resulting in a reduction of lag period by one week, (3) the increase in yield is largely from smear negative specimens and (4) there is no significant increase in the contamination rate to offSummary : To study the effect of carbon dioxide on the primary isolation of mycobacteria, 1005 clinical specimens were inoculated on Lowenstein Jensen’s medium and incubated in an atmosphere with or without additional 10% carbon dioxide. Of the total positive cultures, 30.8% grew only under 10% carbon dioxide and in 58.3% growth was first seen in that atmosphere. Of the positive cultures by either method, 13.4% were positive during the first week when grown with 10% carbon dioxide. Of the culture positives, 21.4% and 15.1% were obtained with 10% carbon dioxide incubation and without additional carbon dioxide respectively. The results of this study show that (1) 10% carbon dioxide increases the yield of mycobacteria in primary culture, (2) it stimulates the temporal growth rate resulting in a reduction of lag period by one week, (3) the increase in yield is largely from smear negative specimens and (4) there is no significant increase in the contamination rate to offset the stimulatory effect on mycobacterial growth. CO2 on an egg based medium6,7,8 and some of their studies have shown that CO2 stimulates and enhances growth on LJ medium.7,8 In earlier studies, an atmosphere of 2 to 5% CO2 had been used but later studies9 indicated that 10% CO2 was the optimum concentration for the growth of tubercle bacilli isolated from clinical specimens while a concentration of 40% may be lethal to mycobacteria. The present study was undertaken to evaluate the effect of 10% CO2 on the primary isolation of mycobacteria grown on LJ medium in terms of : (1) positivity rate, (2) improvement in the rate of growth in cultures and (3) the increase in yield is largely from smear negative specimens and (4) there is no significant increase in the contamination rate to offset the stimulatory effect on mycobacterial growth.

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