Question

QUESTIONS 1) Are acid fast cells gram positive or gram negative? Explain why it might be difficult to determine the Gram reaction of acid fast cells.

Answer 1

Acid-fast bacteria are gram-positive. These Acid-fast organisms contain large amounts of lipid called mycolic acid. Mycolic acids resist staining by ordinary Gram stain methods. Therefore, it might be difficult to determine the Gram reaction of acid fast cells.

Mycolic acids make the organism more resistant to dehydration and chemical damage. They limit the effectiveness of biocides and hydrophilic antibiotics.

Carbol fuchsin is more soluble in the cells wall lipids that is mycolic acids. Therefore, acid fast bacteria will not be destained and retain the color red, while nonacid fast bacteria will be destained and finally appear as blue/green with the counterstain.

When count the number of colonies on a plate, one colony comes from one cell that divides exponentially. A pure culture is a culture that is derived from one bacterial cell so it contains only one species. Yes, the components from the mixed culture just need to be separate first. This can be done by doing a streak plate or diluting the mixture and using a spread-plate technique.