Question

describe methods to detect bacterial flagella

Answer 1

Ans- The presence of flagella ( tail- like structure) in a bacterium shows that it is motile. There are a number of methods to detect motility ( presence of flagella) in a bacterium. These are described below-:

a) Flagellar staining- A flagellar stain known as Hardy Diagnostics flagellar stain helps in detecting the presence and arrangement of flagella in a bacterial cell. Bacterial flagella can be observed by using crystal violet in an alcoholic solution as the primary stain. During the process, the alcoholic solution evaporates leaving a precipitate around the flagella, increasing the size of the flagellum to be visible to the human eye. This stain also comprises of tannic acid and aluminium potassium phosphate as mordants and phenol as an antifungal agent.

b) Motility test medium- This method demonstrates bacterial motility by their ability to swim in a semi-solid medium. This medium is inoculated with the bacteria in a straight line stab with an inoculating needle. If turbidity ( cloudiness) appears due to bacterial growth away from the line of stab, it shows that the bacteria were able to swim through that medium.

c) Direct microscopic observation- Living bacteria are taken in a wet mount. Most bacteria move back and forth in a wet mount. Such a movement is known as Brownian movement that takes place due to random collisions between the bacterial cells and the water molecules. Confirmation of true motility is observed when the bacteria swim from one side of the microscopic field to the other side.