 Dr. O'Hare, everybody, Dr. O'Hare. Quick video, I just want to cover the atypical cell walls, so I've covered the gram-positive and gram-negative cell walls in another video. But when I think of atypical cell walls, I generally think of two things. Number one would be wall-less bacteria, so there actually are some bacteria that don't need cell walls. Now, they're very rare. The only real important genus to mention is the mycoplasma, and the reason they can get away with not having a cell wall appears to be two-fold. Number one, they're tiny. They're actually the smallest known bacteria that can reproduce outside of a host cell. So they're almost blurring the lines between a bacteria and something closer to a virus, I guess you would say. And the second thing is these mycoplasma have some sterols inside their plasma membrane. See, we have sterols in our plasma membranes, which is the reason we don't need cell walls. Our sterol is cholesterol, so they don't have cholesterol, but they have a cousin of it, and it does seem to function the same way. So between the fact that they're tiny and they have these sterols, they're wall-less bacteria. So, but the most important one would be these here, and this would be the acid-fast bacteria. You see, this image has them labeled as gram-positive, and it is true. Now, they would not stain with the gram stain because of this Waxi-Mycolic acid layer, but if you were to remove that Waxi covering, they would stain gram-positive. So you can call them gram-positive acid-fast bacteria, but I like to just call them acid-fast bacteria. So the two genus, the two examples we care about would be the mycobacterium and then any pathogenic strains of nocardia, but those are like exceeding the rare. The mycobacterium, what we care about mainly because of one, mycobacterium tuberculosis, the causative agent of TB, but you do also have mycobacterium lepre, which causes leprosy or Hansen's disease. So what you see here, and this picture doesn't do it justice, is this Mycolic acid. So up to 60% of the cell membrane surrounding acid-fast bacteria is going to be Mycolic acid. It is a Waxi hydrophobic water-fearing covering that's going to cover this organism. That's why it doesn't stain with the gram stain. So let's see, I think that's about it for that. So the two key atypical cell walls would be the walless organisms, think the mycoplasmas, and then the acid-fast bacteria, which have this Waxi Mycolic acid covering around their cell walls. That should do it for cell walls. I hope this helps. Have a wonderful day. Be blessed.