Micro lab exam

Stage - a stage holds the slide.

Substage condenser – Above the light source is a substage condenser which has several lenses that concentrate light on to the slide.

Iris diaphragm – The condenser has an iris diaphragm that controls the amount of light reaching the slide

Objective lenses ( magnification powers) – A revolving nose holding four objective lenses. The magnification is 4, 10, 40, 100. Multiply each lens x 10 to get magnification since the ocular has a magnification of 10.

Coarse adjustment – is used for focusing with low power objectives (4x or 10x)

Fine adjustment – focuses the high power and oil immersion objectives.

Total magnification (powers of each lens) – is 10 x 4 = 40, 10x10=100, (40-45)x10=400, 10x(97-100) = 1000

Oil Immersion lens – The most important lens in microbiology is the oil immersion lens. It has the highest magnification and must be used with immersion oil. The purpose of the immersion oil is to decrease refraction of light while increasing the amount of light directed into the nose piece lens. Immersion oil also enhances the resolution of the image being viewed.

Most bacteria take up a stain that has positive charge.

Positive stains include Methylene blue, safranin, crystal violet, basic fuchsin and gentian violet.

Cocci – refers to round bacteria which can have a variety of arrangements.

Diplococci – round bacteria which appear in pairs

Streptococci – round bacteria which appear in chains of four or more cells.

Tetrads – describes four cells in a square or boxlike arrangement.

Sarcinae – eight cells in a cubicle package

Staphylococci – irregular grape like clusters.

Bacilli – Rod shaped bacteria.

Negative stain (definition/function) – does not stain bacteria but provides a background to view them. This technique reduces the amount of distortion of bacterial cells. This technique is used to examine cell morphology and size. It can be used for the identification of bacterial capsules, spores and difficult to stain bacteria.

The only staining procedure in which neither heat fixing nor strong chemicals are used is Negative Staining.

Negative stains include Nigrosin, india ink and congo.

Differential staining – Procedure was first described in the 1880’s by Hans Christian Gram. It is a differential staining technique which uses two stains or dyes. It allows for classification of many bacteria as gram positive or gram negative.

The primary stain of Gram staining is Crystal Violet.

The mordant of Gram staining is Iodine.

The decolorizing agent of Gram staining is ethyl alcohol.

The second stain of Gram staining is Safranin

Gram positive vs. Gram negative- Those bacteria which are not decolorized are stained purple and called gram positive. The decolorized bacteria that take up safranin are stained read and classified as gram negative. Gram positive bacteria have thick walls which are composed of proteins and cross-linked mucopeptides. Gram negative bacteria cell walls are complex multilayered structured that contain lipids in addition to proteins and mucopeptides.

Acid fast staining technique is an important diagnostic procedure for identification of pathogenic members of Mycobacteria.

Ziehl-Neelson method - most widely used procedure for acid fast staining.

The primary stain of acid fast staining is carbolfuchsin

The counterstain of acid fast staining is methylene blue.

Acid-fast vs. Non acid-fast – Bacteria which retain the primary stain are called acid fast while those that are decolorized and take up the counterstain are referred to as non acid fast. Bacteria which are acid-fast resist staining by other techniques due to th presence of a wax-like lipid mycolic acid, in the cell wall which makes it impermeable to there stains. The cell was of acid-fast bacteria prevents the stain form leaving the cell.

Most common staining technique for viewing spores --Schaeffer-Fulton

Positive staining for spores --Schaeffer-Fulton

Negative stain for spores --Crystal Violet

2 positive staining procedures for viewing capsules --Anthony's and Hiss'

Monotrichous – a single flagellum extends from the cell

Lophotrichous – several flagella project from one pole of the bacteria

Amphitrichous – flagella extend out from both poles of the cell.

Selective media – are designed to promote the growth of certain groups of bacteria while inhibiting the growth of undesired bacteria

Differential media – A media my be differential if their nutrient makeup allows for distinguishing between bacteria on the basis of their metabolic properties.

Examples of dual purpose media (selective and differential) for examination of gram negative bacteria -MacConkey and Eosin-methylene blue (EMB)

Examples of dual purpose media (selective and differential ) for examination of gram positive bacteria -Mannitol salt agar

Enriched media – Are generally formulated to enhance the growth of difficult to grow or fastidious bacteria.

blood agar

• Apha
• Beta
• Gamma

Alpha hemolysis – incomplete lysis of RBC with a green, cloudy zone around the bacterial colony.

Beta hemolysis –complete destruction of the RBC and a clear edge around the colony

Gamma hemolysis - a lack of any hemolytic activity.

Aerobes – need oxygen for growth.

Obligate aerobes – can only grow in the presence of oxygen

Anaerobes –bacteria that can not survive in the presence of oxygen.

Strict or obligate anaerobes – Can not survive in the presence of oxygen.

Facultative anaerobes – Can grow with or without oxygen

Aerotolerant anaerobes – Can not use oxygen but can tolerate it fairly well

Microaerophilic – grow best in decreased concentrations of oxygen.

Capnic – bacteria that have an increased need for carbon dioxide. Require 3–10% of CO₂

They infect a host cell and use its metabolic components to produce more virus particles. Ultimately, the bacterial cell is destroyed by lysis and mature virions are released. Some bacteriophages are temperate. They do not destroy their host but become prophages which enter a lysogenic cycles with the host. These prophages replicate with the host cell and are passed on to succeeding generations. If certain conditions change however, the prophages can be induced into a lytic cycle and cause destruction of the host cell.

Temperate – These viruses do not cause lysis and eath of the host cell. They break the cell wall. Proceeds through the lytic cycle, but only incorporate their DNA into the host cell’s DNA – the phage remains inactive

Prophages – Is when a cell has DNA from a cell and virus.

Lysogenic cycle – This cycle does not lyse the cell