Which other Mycobacterium species grows on MacConkey agar in 5 days?

Which other Mycobacterium species grows on MacConkey agar in 5 days?

• A. M. kansasii
• B. M. bovis
• C. M. tuberculosis
• D. M. chelonei

Answer: (D)

Rapid-growing non-tuberculous mycobacteria can appear on MacConkey agar within a few days, whereas the classic slow-growing TB complex species and other slow growers need specialized media and much longer incubation. Mycobacterium chelonae is one of those rapid growers that readily produces colonies on MacConkey, typically within a few days (about five days in this scenario). The other listed species—Mycobacterium kansasii, Mycobacterium tuberculosis, and Mycobacterium bovis—are slow growers and generally do not form colonies on MacConkey in such a short time; they require media like Löwenstein-Jensen or Middlebrook and longer incubation. So the best answer is the rapid-growing Mycobacterium chelonae.

Rapid-growing non-tuberculous mycobacteria can appear on MacConkey agar within a few days, whereas the classic slow-growing TB complex species and other slow growers need specialized media and much longer incubation. Mycobacterium chelonae is one of those rapid growers that readily produces colonies on MacConkey, typically within a few days (about five days in this scenario). The other listed species—Mycobacterium kansasii, Mycobacterium tuberculosis, and Mycobacterium bovis—are slow growers and generally do not form colonies on MacConkey in such a short time; they require media like Löwenstein-Jensen or Middlebrook and longer incubation. So the best answer is the rapid-growing Mycobacterium chelonae.