Sass

1. The microbe is found in all cases of the disease but is absent in healthy individuals

2. The microbe is isolated from the diseased host and grown in pure culture

3. When the microbe is introduced into a healtjy susceptible host the same disease occurs

4. The same strain of microbe is obtained from newly diseased host

• Louis pasteur developed the first vaccines based on attenuated (weakened strains)

• Principle of immunization: stimulation of an immune response by deliberate inoculation with an attenuated pathogen

• 1929 Alexander Fleming discovered penicillium mold

• 1941 howard florey and Ernst chain pufified penicillin: first commercial antibiotic

Bacilli=rods

Spirochetes=spirals

Cocci=spheres

• generates dark image of an object over lught background

• To increase resokution: - use shorter wavelength light - lessen contrast - use immersion oil - use wider lens closer to specimen - higher numerical aperature (NA)

• Light interacts with an object

A: Absorption: photons energy is acquired by the absorbing object

B: Reflection: Waverfront bounces off the surface of an object

C: Refraction: Bending of light as it enters a substance that slows its speed

Refractive index (n) of the medium containing the light cone, multiplied by the sine of the angle of the light cone (theta)

-> higher NA allows higher resolution

-> wider lens closer so specimen

Prevents light rays from bending away from the objective lens

-> more light is collected NA increases & resolution improves

Cells are made to adhere to a slide in a fixed position

Cells are given a distinct color

-> most stains have conjugated double bonds or aromatic rings and one ore more positive chearges

Adds a dark color to cells but not the surrounding tissue/medium

E.g. methylene blue

Stains one kind of cell but not another

E.g. Gram stain

• 1884 by Christian Gram

• Gram+: retain crytal violet stain (thicker cell wall)

• Gram-: dont retain crystal violet stain

Carbolfuchsin used to stain Mycobacterium species

Malachite green used to detect spores of Bacillus & Clostridium

Colors the background, which makes capsules more visible

• the specimen absorbs light of a defined wavelenght (excitation wavelenght) & emits light of lower energy thus longer wavelength (emission wavelength)

• Used to view bacteria or localize structures/protein

Filters are used to limit:

• incident light to the wavelength of excitation

• Emitted light to the wavelength of emission

• a fluorophore is a fluorescent chemical compound

• Cell specifity can be determined in three ways: - chemical affinity - DNA haybridization - labeled antibodies/proteins

Can be used to view low contrasr live cells and cellular organells (so stain necessary)

Superimposes refracted light & transmitted light shifted out of phase

The light from the specimen & the transmitted light are fully out of phase: specimen apears dark

• electrons pass through the specimen

• Reveals internal structures (2D)

• electrons scan the specimen surface

• Reveals external features in 3D

• Sample must absorb electrons: coated with heavy metals -> unable with living cells

• measures the van der waals forces between electron shells of adjacent atoms of the cell surface & the sharp tip

• It can be used to observe live bacteria in water or exposed to air

• phospholipid bilayer

• 50% proteins

• Hopanoids/cholesterol regulate fuidity

• Semipermeable barrier

• Small uncharged molecules (O2/CO2) can pass by diffusion

• Water can pass by osmosis

• Polar molecules & charged molecules require transport protein

• a phospholipid consits of glycerol with ester links to two fatty acids and a phosphoryl head group (Archaea: ether links)

• structural support

• Detection of environmental signals

• Secretion of virulence factors & communication signals

• Ion transport & energy storage

• Hydrophilis & hydrophobic regions that lock the protein in the membrane

Molecules move along their concentration gradient

Molecules move against their concentration gradient

• confers shape & rigidity & helps to withstand turgor pressure

• Made up of peptidoglycan (murein)

• long polymers of N-acetylglucosamine & N-actetylmuramic acid

• Bound to a peptide of four to six amino acids

• Further peptides can from cross-bridges connecting the parallel glycan strands

• Unique to bacteria

Inhinbits the transpeptidase that cross-link the peptides

Prevents cross-bridge formation by binding to the terminal D-Ala-Ala dipeptide

• multiple layers of peptidoglycan threaded by teichoic acids (LTA/WTA)

M. Tuberculosis & M. Leprae have more complex cell envelopes

Unusual membrane lipids (mycholic acids) & unusual sugar (arabinogalatan)

• thin peptidoglycan layer of one or two sheets

• Covered by an outer membrane with defensive abilites & toxigenic properties: - inward facing leaflet includes lipprotein - outward facing leaflet inculdes lipopolysaccharides - porines

Membrane proteins and secreted proteins are synthesized in contact with the membrane

Signal recognition particle (SRP) binds to growing peptide for insertion into the membrane

Forms ring like structure at the future division site

Forms a coil inside rod shaped cells

= nucleotide occlusion system

Helps FtsZ to find the middle of the cell

Inhibitor at DNA areas -> after duplication: inhibitor free zone

Polar exclusion

Detects curvage regions of the cell and prevents FtsZ