An acid-fast staining method was performed on a bacterial smear using the dyes carbol fuchsin and methylene blue. The resulting stained slide contained only cells that appeared blue when visualized using a microscope. Which of the following could explain why only blue cells were present? a. No acid-fast bacteria are present on the slide
b. Methylene blue was not used
c. Carbolfuchsin was not used
d. Acid-alcohol was not used

Only blue cells where present because No acid-fast bacteria are present on the slide. The correct option is A.

Explanation:

Acid fast staining method also called Ziehl-Neelsen (Zn) technique is used in the laboratory to stain samples suspected to contain Mycobacterium species. The Mycobacterium species which includes the M. tuberculosis, M. ulcerans, and M. leprae, do not stain well by the Gram technique, which is a common routine stain in the laboratory. This is because of waxy coating on its cell surface primarily due to the presence of mycolic acid.

The acid fast stain consists of:

--> A primary dye which is the carbol

fuchsin

--> A decolorizer which is the acid alcohol

--> A counter stain which is the methylene blue.

In it mechanism of action on the bacterial smear, when the primary dye is applied,the whole cell will appear red. But after decolorizing with acid alcohol, only acid fast bacteria will retain the red colour of carbol

fuchsin while the red dye from the background cells are removed. Then the counterstain (methylene blue) is applied which is picked up by non-acid-fast bacteria making the cells appear blue under the microscope.

Therefore when the bacteria smear is viewed under the microscope and only blue cells are seen, it means No acid-fast bacteria are present on the slide.