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Types of microscopes and their utility (e.g., to observe stained vs. unstained objects, to observe motility, etc).
Brightfield: to observe stained material, general microscopy
Darkfield: background is dark, object is bright; especially good for motile cells
Phase Contrast: detailed examination of internal structures in living microorganisms, 3D, shows detail of non-stained cells
Fluorescent: uses UV light, fluorescent stained cells or structures will glow with color
Transmission electron microscope: shows internal cellular organelles greatly magnified, can also be used to observe viruses in sections
Scanning electron microscope: shows 3-D surface structures of cells or viruses highly magnified
What are fomites?
Any inanimate object or substance capable of carrying infectious organisms and hence transferring them from one individual to another
Examples: cloth or mop head, skin cells, hair, clothing, and bedding
Normal flora vs. transient flora: which ones does hand washing get rid of?
Normal flora: resident, live naturally and permanently on our skin, not readily removed by mechanical friction
Transient flora: microbes that are temporary also called non-colonizing or contaminating flora; easily removed by mechanical friction/hand washing
Terms associated with microscopes: resolution vs. magnification
A. Resolving power or resolution is defined as the closest distance two objects can be, where we can still see them as separate objects
Resolving Power= Wavelength/(2 X Numerical Aperture)
Numerical aperture is inscribed on the barrel of the objective lens
4X Scanning= (4 X 10) Magnification
10X Low Power= (10 X 10) Magnification
40X High Dry= (40 X 10) Magnification
100X Oil Immersion= (100 X 10) Magnification
Purpose of various types of medium: selective, enriched, and differential medium
Selective: only allows certain species to grow and inhibits others
EMB agar—inhibits gram-positive bacteria and select gram-negative species
Enriched: contains added nutrients to enhance the growth of those finicky bacteria with a gourmet appetite
Blood agar—used for growing certain pathogenic microbes
Differential: has a diagnostic test built into it that changes colors with different species of microbes
Lactose broth will turn from red to yellow for species that can ferment lactose but not for those that can't
Shapes of bacteria and examples
-Coccus (plural: cocci, meaning berries)=spherical
Bacillus (plural: bacilli, meaning little staffs)=rod-shaped
Spiral or coiled
Cocci are usually round but can be oval, elongated, or flattened on one side
Diplococci—cocci that remain in pairs after dividing
Streptococci—cocci that divide and remain attached in chain-like patterns
Staphylococci—divide in multiple planes and form grapelike clusters
Staphylococcus aureus (abscesses)
Tetrad—cocci that divide in 2 planes, remain in groups of 4
Sarcinae—cocci that divide in 3 planes, cube-like groups of 8
Bacilli are not usually subdivided by arrangement, only subdivided by other properties (e.g. Gram stain)
Vibrio cholerae (cholera)
Escherichia coli (urinary tract infections)
Bacillus anthracis (anthrax)
Rigid helix (twisted twice or more along its axis, like a corkscrew)
Campylobacter jejuni (diarrhea)
Flexible spirals (spirochetes)
Treponema pallidum (syphilis)
Structural components of bacteria and their function: capsule (role in pathogenesis), cell wall, flagella (what is an axial filament?), fimbria, and endospores.
Capsule—external to cell wall, organized and firmly attached to the cell wall, protect pathogenic bacteria from phagocytosis by the cells of the host; gummy consistency that gives colonies sticky (mucoid) characteristic)
Two types of Streptococcus pneumoniae
Cell wall—prevents cell from blowing up by hypotonic solution, gram-positive and gram-negative, major target for drugs
Flagella—major function is motility
Axial filaments—spirochetes are flexible because of this (periplasmic flagella), contractile filaments, length of spirochete, flagella enclosed in the space between the cell wall and cell membrane
Fimbriae—hollow tubes of protein, not for locomotion
Shorter, numerous, for adhesion
Endospores—called endospore when still inside rod, made when essential nutrients are depleted, function for survival in heat, drying, chemical disinfectants, and radiation
Cell wall is a good target for what anti-microbial drugs? What molecule on a Gram-negative bacterial cell wall acts as a deadly virulent factor?
Penicillin—blocks amino acid cross bridges in peptidoglycan
Lysozyme—digests bonds between NAG & NAM in peptidoglycan
Lipopolysaccharide (LPS) of the outer membrane of gram-negative bacteria is a large complex molecule that contains lipids and carbohydrates
When gram-negative bacteria die, they release lipid A, which functions as an endotoxin
A toxin that is a structural molecule of the bacteria that is recognized by the immune system
What are the reagents used in the steps of Gram stain?
Crystal violet (primary stain): stains all bacteria purple
Gram's Iodine (mordant): causes a stain to become more tightly bond to the cell by intensifying the ionic chemical bond between the crystal violet and the bacteria
Ethyl alcohol (decolorizer): removes the stain from gram-negative bacteria, which now becomes colorless
Safranin (counterstain): stains any colorless cells, stains gram-negative bacteria red
Hypertonic vs. hypotonic solution (what happens to cells in each of these solutions?)
Hypertonic—solution has more solutes than the cell, plasmolysis (shriveling)
Hypotonic—solution has very little solutes, Plasmoptysis (swelling up of cell)
Eukaryotic cell components and functions: Cell membrane (phospholipid bilayer), RER (rough endoplasmic reticulum)
Cell membrane—two layers of phospholipids with proteins embedded and sterols (confer stability)
RER—site of protein synthesis, ribosomes
Viral structural components (envelope, nucleocapsid, peplomer, etc.)
Envelope—membrane that encloses virus, protein and lipid-sometimes called viral membrane
For enveloped viruses, this is the virion or virus particle
Nucleocapsid—capsid (viral protein) + genome (RNA or DNA)=nucleocapsid
For non-enveloped viruses this is the virion or virus particle
Peplomer—viral glycoproteins embedded in the envelope, receptor for virus
What determines the host specificity of a virus? (Why doesn't hepatitis virus infect muscle cells?)
Specificity normally resides at the cell surface virus receptor level
Human cells do not have receptors for viruses that infect cats
Muscle cells do not have receptor for hepatitis, the liver does
How do interferons protect a viral infection?
Interferons are natural compounds produced in the body during a virus infection. They inhibit virus replication and virus infection of adjacent cells. Cells make interferons even before immunity kicks in, part of the first line of defense. Can be made by every cell (except RBC); make proteins to chop virus
Definitions of phototroph, chemotroph, autotroph, heterotroph: pathogens are?
Phototroph—photosynthetic, sunlight as energy source
Chemotroph—organic chemicals as energy source
Autotroph—CO2 as carbon source
Heterotroph—organic chemicals as carbon source
Chemoheterotroph=man, animals, most bacteria: pathogenic bacteria
Definitions of aerobic, anaerobic, facultative aerobic (bacteria)
Aerobic—grows in the presence of oxygen
Anaerobe—grows best without oxygen
Facultative anaerobe—use oxygen if its available, but they can also survive without it, grow all throughout the medium
What are halophiles? Saprobes (such as fungi)?
Halophiles: are organisms that require a high salt concentration for growth. Live in habitats with a high solute concentration, like the ocean
Saprobes: are organisms that obtain its nutrients from dead organic matter
Temperture range for: psychrophiles, mesophiles, thermophiles
Psychrophiles—cold loving, 0-20 C
Mesophiles—moderate temperature loving, 20-45 C
Thermophiles—heat loving, 45 and up C optimum growth temperatures
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