Mycobacterial culture and sensitivity

Why is mycolic acid resistant to staining?

Mycolic acids make the cell wall extremely hydrophobic and enhance resistance to staining with basic aniline dyes so mycobacteria are not visible with the Gram stain. Under certain conditions arylmethane dyes are able to form stable complexes with the mycolic acids within mycobacterial cell walls.

What makes Mycobacterium resistant to staining? Mycobacterium has a waxy cell wall that contains mycolic acid, a complex lipid that prevents stains from penetrating the cell .

tuberculosis has an unusual, waxy coating on its cell surface primarily due to the presence of mycolic acid . This coating makes the cells impervious to Gram staining, and as a result, M. tuberculosis can appear weakly Gram-positive.

Acid-fast bacteria, of which there are very few---the major genus Mycobacterium, have a high concentration of mycolic acid, a lipid, in their walls . Although difficult to stain, once the stain goes into the wall, the cell will not de-stain or decolorize easily.Aug 1, 2021

Is Mycoplasma Gram-positive?

Mycoplasma are the smallest of all prokaryotic microbial cells, Figure 5.10(A) and (B). Figure 5.10. (A) Mycoplasma pneumoniae cells (Gram stain). The signet-ring-shaped cell of Mycoplasma is gram-negative , and the size of the cell is 0.2–0.3 μm and is normally smaller than 1.0 μm.

Mycobacteria are Gram-positive , catalase positive, non-motile, non-spore forming rod-shaped bacteria (0.2–0.6 μm wide and 1.0–10 μm long).

While Mycobacteria do not seem to fit the Gram-positive category from an empirical standpoint (i.e., they do not retain the crystal violet stain), they are classified as acid-fast Gram-positive bacteria due to their lack of an outer cell membrane . M.

In fact, it is very difficult to stain any mycobacterium . There is one specific technique to stain mycobacterium: the Ziehl-Neelsen stain, named after the two German doctors who first described it. When stained with a Ziehl-Neelsen stain, the mycolic acids take on the color quickly and retain them inside the bacillus.

Does Mycobacterium stain Gram-positive or negative?

Mycobacteria are Gram-positive , catalase positive, non-motile, non-spore forming rod-shaped bacteria (0.2–0.6 μm wide and 1.0–10 μm long). The colony morphology of mycobacteria varies with some species growing as rough or smooth colonies. Colony colour ranges from white to orange or pink (Iivanainen, 1999).

The Ziehl-Neelsen stain uses basic fuchsin and phenol compounds to stain the cell wall of Mycobacterium species. Mycobacterium does not bind readily to simple stains and therefore the use of heat along with carbol-fuschin and phenol allows penetration through the bacterial cell wall for visualization .