RE: Microbiology #1 : The Notoriously Pathogenic Mycobacterium tuberculosis and its Mycolic Acid fortress
sugary arabinogalactan. They can be classified under the gram positive bacteria category but they do not stain like them
Yeah, staining them is a PITA.
Mycobacterium only flowers in rich media and multiplies every 16-20 hours, which is sluggish as compared to other bacteria
The slow growth rate has been postulated as to why it took so long for them to be isolated. A lot of plates are incubated for 24 to 72 hours. For a lot of bugs, this is a ton of doubling times (as in your E. coli example, this is 72 to 216 doublings - far enough time for visible colonies. For Mycobacterium, that could be as few as 6 doublings in about a week. We now think that earlier bacteriologists may have done everything right for isolation, but just simply assumed nothing was growing.
Thanks for the detailed info. They do grow very slowly huh. I bet this caused a lot of hassle especially to diagnose tuberculosis especially many years ago. Staining works but I don't think the sensitivity rate is as high as culturing. Furthermore, we need the culture results for the antibiotics susceptibility testings as some mutated strains are resistant to certain common anti-tb drugs.