Motility of bacteria 4

Bacterial motility

Motility
means that microorganism change its position or move from place to place by using the major organelles of motility( flagella), flagellum consists of protein called flagellin
is a rigid helical structure that can extend as much as 10 microns out from the cell .but they are very thin structures ,less than 0.2 microns, and therefore ,they are below the resolution of light microscope
Flagellum

Function of motility : 

Increase the uptake of nutrient materials by continuous movement . Assist the bacteria to move away from harmful substance such as acid in a complicated process called (chemotaxis) Assist the pathogenic bacteria in penetration and invasion Motility and arrangement of flagella around the cell are useful in characterizing them

Classes of motile bacteria

Monotrichous (single polar flagella) e.g. Pseudomonas aeroginosa & vibrio cholerae Peritrichous (many flagella surrounded body cell) e.g. Salmonella typhi & Proteus spp . Lophotrichous (tuft of flagella at one pole of the cell) e.g. Spirillum spp . Amphitrichous (either single flagella or tuft of flagella at the two poles . e.g.Pseudomonas spp .

The flagella pattern is an important feature in identification of motile bacteria.

Site of flagella
Peritrichous (E.coli) Monotrichous ( Vibrio cholerae)


Site of flagella
Lophotrichous (pseudomonas) amphitrichous (Spirillum volutans)

bacteria possess two kinds of movement

True movement: bacteria move by using flagella. Brownian movement : Its an oscillatory movement which possessed by all small bodies suspended in fluid whether living or not.

Motility testing

Motility could be detected by: Flagellar stain. Hanging drop technique. Semi-solid media Inoculation.

1- Flagella stain

Flagella are too thin to be seen by the ordinary light microscope.Flagella should be amplified (enlarged). Use a stain that is specifically precipitated on Flagella thus increasing diameter.Some flagellar stains employ1- rosaniline dyes and a mordant, applied to a bacterial suspension fixed in formalin and spread across a glass slide. The formalin links to, or “fixes,” the flagellar and other surface protein of the cells. The dye and mordant then precipitate around these “fixed” surfaces, enlarging their diameters, and making flagella visible when viewed under the microscope.Another method, a2- ferric-tannate mordant and a silver nitrate solution are applied to a bacterial suspension. The resulting dark precipitate that forms on the bacteria and their flagella allows them to be easily to seen under the microscope. This silver-plating technique is also used to stain the very slender spirochetes.

Rosanalin dye silver nitrate + ferric tannate

2-Hanging drop methodProcedure :
By using concave slide if available, other wise ordinary slide will do . By means of stick dipped in vaseline, a ring or a square (according to the shape of the cove slip) is out lined. With a wire loop, place a drop of broth containing bacteria on a cover slip, take care to avoid contamination of culture by open the mouth of the tube near the flame .



3-Semi solid media
Materials : Semi solid nutrient agar . Young culture of motile bacteria & non motile bacteria . Inoculating wire

Semi solid media

Semi solid media
Motile bacteria
Non-motile bacteria

Semi solid media with tetrazolium chloride (color indicator)

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