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25 terms

Microbiology Chapter 3

STUDY
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simple microscope
microscope has only one lens.
compound
In this microscope the image from the objective lens is magnified again by the ocular lens.
Total magnification = objective lens x ocular lens
Resolution
the ability of the lenses to distinguish two points.
Limit of Resolution for the light microscope is 0.2 mm.
A microscope with a resolving power of 0.2 mm can distinguish between two points ≥ 0.2 mm.
brightfield illumination
Dark objects are visible against a bright background.
Light reflected off the specimen does not enter the objective lens.
darkfield illumination
Light objects are visible against a dark background.
Light reflected off the specimen enters the objective lens
phase-contrast microscopy
Accentuates diffraction of the light that passes through a specimen.
differential interference contrast microscopy
Accentuates diffraction of the light that passes through a specimen; uses two beams of light.
fluorescence microscopy
Uses UV light. Fluorescent substances absorb UV light and emit visible light. Cells may be stained with fluorescent dyes (fluorochromes).
confocal microscopy
Uses fluorochromes and a laser light. The laser illuminates each plane in a specimen to produce a 3-D image.
electron microscopy
Uses electrons instead of light. The shorter wavelength of electrons gives greater resolution.
Transmission Electron Microscopy (TEM)
Ultrathin sections of specimens. Light passes through specimen, then an electromagnetic lens, to a screen or film.
Specimens may be stained with heavy metal salts. 10,000-100,000x; resolution 2.5 nm
scanning electron microscopy (SEM)
An electron gun produces a beam of electrons that scans the surface of a whole specimen. Secondary electrons emitted from the specimen produce the image.1000-10,000x; resolution 20 nm
Smear
A thin film of material containing microorganism on the slide.
Fixation
Process to preserve microbe and attach it to the slide. (Heat)
Staining
addition of a dye to add color to the microorganism.
Stains
consist of salts with a positive and negative ion.
Bacteria have slight negative charge at pH=7. Therefore, Basic dyes commonly used to stain bacteria.
Some basic dyes: Crystal Violet, Methylene blue, Malachite Green, Safranin.
basic dye
In a ---, the chromophore is a cation. Bacteria have slight negative charge at pH=7. Therefore, this type of dye is commonly used to stain bacteria. ex: Crystal Violet, Methylene blue, Malachite Green, Safranin.
acidic dye
In an ----, the chromophore is an anion.
Simple Stain
Use of a single basic dye to highlight entire microorganism is called a ----.
Differential Stains
React differently with different species of bacteria, therefore can be used for identification. (ex. Gram stain, Acid-Fast stain)
mordant
A ---- may be used to hold the stain or coat the specimen to enlarge it.
Gram-positive
bacteria tend to be killed by penicillin and detergents.
Gram-negative
bacteria are more resistant to antibiotics.
Acid-Fast stain
binds strongly to bacteria with waxy lipids in cell wall.
Mycobacterium tuberculosis and Mycobacterium leprae are two important pathogens identified.
Primary stain - Carbolfuchsin (Red)
Acid-fast microbes retain red primary stain.
Counterstain - Methylene Blue
Non Acid-Fast cells are blue
Special Stains
are used to color and isolate specific parts of microbes.
1. Capsule - Gelatinous covering of microbe.
2. Endospore - A special dormant structure that survives adverse environmental conditions.
Primary stain - malachite green.
Counterstain - safranin.
Endospores appear green within red/pink cells.
3. Flagella - Structure of locomotion.