Lab 3 Report- Exercise 17

Describe the structure of a flagellum. How do flagella generate motility?

-Bacterial flagellum = fibrous appendage composed of protein subunits and anchored in the membrane. -Flagella rotate counterclockwise to propel the cell forward and clockwise to tumble and change direction.

Why are semisolid media sometimes preferred over slide techniques for evaluating bacterial motility?

Exposure of individuals to pathogens is more likely when making wet slides as opposed to stabbing a semisolid medium where the bacteria are contained. There are also fewer false positives when using semisolid medium b/c there is no brownian movement or water current.

Between wet mount and hanging drop slide preparation, which is more resistant to evaporation? Which works best w/ phase contrast microscopy?

Hanging drop = resistant to evaporation Wet mount = better w/ phase contrast

Brownian movement

Jiggling motions without vectorial movement indicate Browman movement.

If you compared two motile species and determined one was considerably more motile than the other, which arrangement of flagella would you expect to be associated w/ the highly motile species? How would you confirm this supposition?

Peritrichous flagela = numerous arrangements across entire cel surface (motile= Proteus) Confirm w/ flagellar arrangement w/ flagella stain

Directional motility

Rapid swimming and directional change indicate true motility

If SIM medium was used for motility determination for Proteus Vulgaris, what noticeable change to the medium was observed?

SIM = semisolid medium that shows motility of P. Vulgaris & sulfide production (Black preoccupation that forms when H2S complexes w/ iron salt)

What concentration of agar is used in a semisolid medium for motility determination? How does that compare to a simple solid medium?

Semisolid = 0.4% agar Solid = 1.5% agar

water current movement

Sweeping motion indicates water currents.