The stimulatory effect of carbon dioxide (CO2) on the growth of tubercle bacilli was reported by a few authors. A study was done to see the effect of CO2 on primary isolation of mycobacteria on Lowenstein Jensen medium in terms of (1) positivity rate (2) improvement in the rate of growth in cultures and (3) contamination rate.

One thousand and five clinical specimens were inoculated, after processing by modified Petroff's method, onto LJ medium and incubated with or without addition of 10% of 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. 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 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 stimulating effect on mycobacterial growth.