Microbio Lab 3 Flashcards
pure cultures
contains only a single kind of an organism, whereas a mixed culture contains more than one kind of an organism; can study morphological and physiological characteristics of an individual organism
streak plate
physical dilution of cells over the plate surface until a single cell is deposited in an area and grows to produce an isolated bacterial colony (quadrant streak method and radiant streak) Requires more skill but less time and materials
pour plate
separating one species of bacteria from another by diluting one loopful of organisms across a series of tubes of liquified nutrient agar in such a way that one of the plates poured will have an optimum number of organisms to provide good isolation requires less technique but requires more time and materials
colony
identical progeny of the original cell and can be picked and used for further study of the bacterium
simple staining
the use of a single stain to color a bacterial cell (methylene blue, basic fuchsin, and crystal violet)
basic dyes
dyes that contain color bearing ionic groups (chromophores) that are positively charged (cationic); stain negative exterior of cell
acidic dyes
dyes that have anionic chromophores; repelled by bacterial cells and stain background of slide
bacillus
rod shaped cells bacilli, coccobacillus, fusiform
cocci
spherical shaped cells diplococci, tetrads, streptococci, staphylococci
spirals
corkscrew shaped rods comma, spirillum, spirochaetes
fusiform bacteria
rod shaped bacteria with tapered ends
pleomorphism
pertains to irregularity of form; demonstrating several different shapes
metachromatic granules
distinct reddish-purple granules within cells that show up when the organism are stained with methylene blue; they are masses of volutin, a polymetaphosphate
palisade arrangement
parallel arrangement of rod-shaped cells
flagella
major organelles of motility in bacteria; allow cells to move toward nutrients in the environment or move away from harmful substances; rigid helical structure
chemotaxis
movement toward nutrients or away from harmful substances
wet mount
A drop of viable cells is placed on a microscope slide and covered with a cover glass; observed using phase-contrast ; dry out easily
hanging drop
a drop of cells is placed on a cover glass, which is then placed over a special slide that has a concave depression in its center; the coverslip is held in place with vaseline and it creates an enclosed chamber which prevents drying
Brownian motion
cell movement caused by currents under the glass; movement due to molecular bombardment of cells causing cells to shake or ‘jiggle’ but not move in any specific direction
monotrichous
lophotrichous
peritrichous
amphitrichous
Robert Koch
Father of medical microbiology; developed isolation methods for obtaining pure cultures of bacteria
Define the term “colony” as it relates to bacterial growth on solid media?
A single pure colony is the identical progeny derived from a single cell. One colony is equal to approximately one billion cells.
What colony characteristics can be used for differentiation of bacterial species? As an example, compare the properties of colonies of Serratia marcescens and Micrococcus luteus on your streak plate.
Useful colony characteristics for differentiation of bacterial species include size, color, shape, texture, opacity, and odor. For example, Serratia marcescens colonies are red, irregular in shape, and have a strong odor. Micrococcous luteus, on the other hand, are yellow, opaque, round, and dome-shaped.
Why is dilution a necessary part of pure culture preparation?
When working with a culture that may contain millions of cells, dilution on a solid medium is essential for separating the cell with enough space so that they can grow into isolated colonies.
What advantages does the streak plate method have over the pour plate method?
Streak-plate method is more economical in materials and time.
What advantages does the pour plate method have over the streak plate method?
Pour-plate method requires less skill, has optimization built it, and will most likely produce the desired result.
Before inoculating and pouring molten nutrient agar into a plate, why must the agar first be cooled to 50 degrees Celsius?
So that microbes added to the medium will not be killed by excessive heat, but it must not be cooled too much because it will solidify before the cells can be dispersed and poured. If too hot when poured, excess moisture will form on the lid of the plate.
Explain why plates should be inverted during incubation?
Plates are inverted so that moisture does not accumulate on the lid and drop to the agar surface. This will cause the organisms to spread and negate the dilution effect. Also agar plates tend to dehydrate faster in the upright position.
Describe the difference between the appearance of surface and subsurface colonies in a pour plate. Why do these differences occur?
Subsurface colonies are small and embedded in the agar. They do not have the identifying characteristics of surface colonies such as edge, surface characteristics, and in some cases, pigment. Subsurface colonies must grow under limited oxygen conditions, which would affect growth and some characteristics.
Flagella structure
A rigid filament that occurs in the form of a helix (constitutes the main part of the flagellum structure). The filament is connected to a hook that is attached to a shaft that is inserted into a series of rings. Gram positive cells possess S & M rings and gram negative cells possess S,M,L, and P rings
How do flagella generate motility?
proton motive force (basal body transports protons across cell membrane)
Which arrangement of flagella would be more likely to be associated with a highly motile species?
lophotrichous; confirm by looking at how far it travels
Differentiate between directional motility, Brownian movement, and water current movement?
Directional motility is movement in random directions, and caused by flagella
Brownian movement is caused by molecular bombardment (jiggling)
Water current movement is movement in the same direction
Between wet mounts and hanging drop slide preparations, which is more resistant to evaporation? Which works best with phase-contrast microscopy?
Hanging drop slides are more resistant to evaporation, although wet mount slides work better with phase-contrast microscopy.
What concentration of agar is used in a semisolid medium for motility determination? How does that compare to a typical solid medium?
A concentration of 0.4% agar is used to make semisolid media, which when stabbed, allow motile bacteria to swim but hold nonmotile in place. Typical solid medium contains 1.5% agar, which when stabbed, would not allow movement of motile bacteria.
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 media because their is no Brownian movement or water current.
If SIM medium was used for motility determination for Proteus vulgaris, what noticeable change to the medium was observed?
SIM is a semisolid medium that will not only show motility (M) of P. vulgaris, but also sulfide production (S), which is visualized as a balck precipitate that forms in the medium when H2S complexes with iron salts
colony not on streak lines
contamination
staphylococcal
cocci in clusters
streptococcal
cocci in clusters
tetrad
four
diplococcus
pairs
motility test
Use semisolid media (0.3 or 0.4% vs 1.5% agar-allows motile bacteria to move through agar)
Contains tetrazolium dye that turns red when there is growth
