Microbiology: Lecture 3

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A Scanning Acoustic Microscope (SAM)

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is a device which uses focused sound to investigate, measure, or image an object (a process called Scanning Acoustic Tomography). It is commonly used in failure analysis and non-destructive evaluation. It also has applications in biological and medical research. The semiconductor industry has found the Scanning Acoustic Microscope useful in detecting voids, cracks, and delaminations within microelectronic packages.

Front 2

Transmission Electron Microscopy (TEM)

Back 2

Ultrathin sections of specimens
Electrons passes through specimen, then an electromagnetic lens, to a screen or film
Specimens may be stained with heavy metal salts

Front 3

Scanning Electron Microscopy (SEM)

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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

Front 4

Scanning tunneling microscopy (STM)

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uses a metal probe to scan a specimen
Resolution 1/100 of an atom
Viewing surfaces at the atomic level. Developed in 1981. STM
When a conducting tip is brought very near to a metallic or semiconducting surface, a bias between the two can allow electrons to tunnel through the vacuum between them. Variations in current as the probe passes over the surface are translated into an image. It requires extremely clean surfaces and sharp tips

Front 5

Atomic force microscopy (AFM)

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uses a metal- and-diamond probe inserted into the specimen.
Produces three-dimensional images.

Front 6

basic dye

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chromophore is a cation

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acidic dye

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chromophore is an anion

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negative staining

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Staining the background instead of the cell

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Simple stain

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Use of a single basic dye

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mordant

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may be used to hold the stain or coat the specimen to enlarge it

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Gram stain

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differentiates between Gram positive and Gram negative bacteria. Classifies bacteria into gram-positive or gram-negative
Gram-positive bacteria tend to be killed by penicillin and detergents
Gram-negative bacteria are more resistant to antibiotics

Front 12

Acid-fast stain

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differentiates between bacteria that have a waxy covering over their cell wall and those who do not. Binds strongly to bacteria that have a waxy material in their cell walls; specifically the genus Mycobacterium, but also pathogenic strains of Nocardia. Mycobacterium tuberculosis and Mycobacterium leprae (causes leprosy) are two important pathogens.
A smear is covered with red carbolfuchsin and gently heated for several minutes. This heating enhances penetration and retention of the dye.
The slide is cooled, washed with water and treated with acid-alcohol (decolorizer) that removes the stain from non acid-fast bacteria.
The smear is counterstained with methylene blue.

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Special Stains

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Used to distinguish parts of cells
Capsule stain
Endospore stain
Flagella stain

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Endospore stain

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(endospores are resistant, dormant structures formed within a cell) Only a few genera of bacteria produce them, including Clostridium and Bacillus.