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Learn the toughest concepts covered in Microbiology with step-by-step video tutorials and practice problems by world-class tutors.

9. Microscopes

Differential Staining



Differential Staining

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in this video, we're going to begin our lesson on differential staining. And so differential staining is actually a staining process that is going to be using multiple dies at once in order to distinguish or as its name implies, differentiate different groups of bacteria. Now the two most common examples of differential stains are the gram stain and the acid fast stain. Now the gram stain is going to differentiate bacteria based on differences in their cell wall. And so the gram stain will help to group some bacteria as gram positive bacteria and other bacteria as gram negative bacteria. And once again, gram positive and gram negative bacteria are going to be differing in terms of their cell walls. And later in our courts, we're going to talk a lot more details about the steps of the gram stain. Now the acid fast stain is another example of the differential stain that is going to identify acid fast bacteria which are bacteria that have a waxy material called my colic acid in their cell walls. And so if we take a look at our image down below what we're showing you are two examples of differential stains on the left. What we're showing you is the example of the gram stain. And on the right, what we're showing you is the example of the acid fast stain. Now the gram stain is going to help differentiate the gram positive bacteria from the gram negative bacteria. And this is because the gram positive bacteria are going to remain a purple color. And so all of these purple bacteria that you see in here are going to be grand positive cells. Now the gram negative bacteria on the other hand, are going to take on a pink color such as estrogen Nicola is an example of a gram negative bacteria. And so all of these pink bacteria that you see throughout here are going to be gram negative and staphylococcus aureus is an example of a gram positive bacteria now over here on the right hand side, what we're showing you is another example of a differential stain called the acid fast stain. And the acid fascinating helps to identify acid fast bacteria, which are bacteria that contain that waxing material, my colic acid in their cell walls. And so mycobacterium tuberculosis bacteria is an example of an acid fast bacteria. And so when using the acid fast stain, this particular bacteria is going to turn a dark purple color as you can see here in this image. And bacteria that are not acid fast are going to not take on this dark purple color. And so really these differential stains help to group bacteria based on specific features that they may or may not have. And so this year concludes our brief introduction to differential standing. And once again, later in our course, will be able to talk a lot more details about the gram stain itself. So I'll see you all in our next video.

A scientist is examining more than one species of bacteria under a microscope at the same time. The scientist decides to differentiate the bacterial cells based on their cell wall/cell envelope structure. Which staining technique should she use?


A scientist has a sample containing a variety of different bacteria species. She wishes to identify which bacteria in her sample are of the genus Mycobacterium. Mycobacterium have a wax-like, nearly impermeable cell wall which contains mycolic acid. Which type of staining technique should the scientist use to identify the Mycobacterium?