Lab Midterm Test Questions – Flashcards

The ability to distinguish two adjacent points as separate objects based upon
resolving power.

Function of Three Things:

1. Numerical aperture
2. Wavelength of light

3. Design of condenser

D =                     Wavelength                         

(N A condenser) + (N A of objective lens)

- have negative (-) charge
- ex. Eosin, nigrosin (india ink), congo red
- can not penetrate the bacteria because the repulsion between the charges
- stains the background

-chromophores have negative charge

Function
1. Increases virulence in some organisms by protecting the cell from phagocytosis by
the immune system because antibodies are hidden
2. Prevents dehydration/desiccation due to the attraction of water by the layer
3. Attachment to host cells because of binding reactions between the host tissue and the glycocalyx

Organisms
1. Klebsiella pneumoniae => has a capsule and looks like a figure eight
2. Staphylococcus epidermidis => has no capsule

Differential staining technique that it used to detect the presence
of mycolic acid.

Mycobacterium

TTC is:

- colorless and soluble when oxidized
- red when reduced
- makes it easy to see the results because the red color appears along the growth pattern

Advantage of Motility Test Media:
- technique can be used to test for the motility of Pathogenic organisms

Disadvantages of Motility Test Media:
- requires incubation time
- if technique is not performed properly, non-motile organisms can appear motile

Synthetic or defined media – exact composition is known; has been synthesized; chemical
compounds used are highly purified and defined

Non-synthetic or complex media – the exact composition is not known; utilizes compounds
that include all the nutrients but they are not defined

media that allows only certain organisms to grow

Selection is based on:

a. Absence of certain nutrients which prevent the growth of some but not all bacteria
b. Presence of a toxic or inhibitory substance like salt, acid, base, chemical (crystal
violet or methylene blue), and antibiotic

- selective and differential media

- contains mannitol, 7.5% NaCl, and the pH indicator Phenol red
- in general, organisms can not grow on this amount of salt. Thus, the media is selective for Staphylococcus species.
- Some species of Staph (pathogenic) have the ability to ferment mannitol.
- Acid is produced if mannitol fermentation occurs. Phenol Red can show the decrease in
pH. It is yellow when the pH is below 6.8, red at pH 7.4-8.4, and pink at above 8.4.
- If the organism is nonpathogenic, then it will grow well on MSA, but will not ferment
mannitol.
- If the organism does not grow well, then it is probably not Staph.

- selective and differential media

- select and differentiate members of Enterobacteriaceae

- contains lactose, bile salts, neutral red, and crystal violet
- Gram positive organisms are inhibited by the bile salts and crystal violet
- Some organisms have the ability to ferment lactose to acid
- Indicated by the neutral red which is red at pH below 6.8 and colorless at pH above 6.8.
- Red is indicative of lactose fermenters
- Colorless is indicative of non-lactose fermenters

- is a selective and differential media

- contains peptone, lactose, sucrose, eosin, and methylene blue
- The sugars provide fermentable substrates that promote the growth of fecal coliforms
- Methylene blue inhibits the growth of Gram positive bacteria
- Eosin is an acidic dye that differentiates on the basis of fermentation
- Green metallic sheen to deep purple is indicative of fecal coliforms.
- Pink is indicative of low acid production or slow fermenters.
- Colorless or same color as the media is indicative of nonfermenters.

- is a selective and differential media

- isolate Salmonella and Shigella species from other enterics

- contains peptone, lactose, sucrose, salicin, bile salts, sodium thiosulfate, ferric ammonium
citrate, bromthymol blue, and acid fuchsin
- The sugars (lactose, sucrose, and salicin) provide fermentable substrates that promote the growth
of fecal coliforms
- Sodium thiosulfate acts as a source of sulfur.
- Ferric ammonium citrate reacts with H2S produces by the reduction of sulfur to form a black
precipitate.
- Bile salts inhibit the growth of most Gram positive bacteria
- Bromthymol blue and acid fuchsin dyes act as color indicators to indicate the fermentation of
sugars and production of acids that lower the pH of the medium.
- Enterics that produce acid from fermentation will produce yellow to salmon-pink colonies.
- Bacteria that do not ferment any of the sugars will produce blue-green colonies.
- Bacteria that reduce sulfur to H2S form colonies containing a black precipitate

- grows molds

- has a pH of 5.6 which inhibits
bacterial growth

1. Quantitative Plating (Standard/ Viable Plate Count)

2. Turbidity measurement
(using a Spectrophotometer)

(DF)= Vol added to the dilution blank
               Total volume in the tube

Original Cell Conc.=  number of colonies

                                (volume plated) (FDF)

pipettes that have graduations down to the tip.

Two types of Serological Pipettes
A. TC (“to contain”) – these pipettes expel all the volume down to the tip, then the
last drop must be “blown out” using the pipette pump or syringe
B. TD (“to deliver”) – these pipettes expel all the volume down to the tip, but the
last drop should not be blown out

Virus Infection Units

Smallest unit causing an effect with a host

- Plaque Forming Units

- Efficiency of count from the assay is always less then with an electron microscope because efficiency of infection by viruses is not 100%