Effect of egg yolk on growth of Mycobacterium tuberculosis in 7H12 liquid medium.

Of 92 drug-resistant Mycobacterium tuberculosis strains isolated from sputum specimens, 86 showed growth in two types of 7H12 broth, one with egg yolk and the other without egg yolk. In addition, two strains grew only in plain 7H12 broth without yolk, and four others were recovered only in the medium supplemented with egg yolk. The radiometrically detected growth was higher in the presence of egg yolk, corresponding to a higher number of CFU per milliliter in these cultures. The improvement of growth in 7H12 broth supplemented with egg yolk was most noticeable in cultures isolated from sputum specimens having a low number of acid-fast bacilli in the smear and producing only a few colonies on solid media.