Flagella Outside cell wall Made of chains of flagellin (vs. tubulin) Certain pathogenic bacteria can be identified by their flagellar proteins. Attached to a protein hook Anchored to the wall and membrane by the basal body animation Figure 4.8
Flagella Usually too small to be seen with a typical microscope – have to study live bacteria to detect mobility. Providing movement (in response to chemicals or light) Chemotaxis (move in response to chemical signals). Positive chemotaxis more runs Negative chemotaxis more tumbles Phototaxis
Axial Filaments Internal flagella In spirochetes Anchored at one end of a cell Rotation causes cell to move Video: Spirochetes the cause Lyme disease Video: Spirochetes the cause Lyme disease Figure 4.10a
Figure 4.11 Fimbriae Fimbriae are small bristlelike fibers that allow attachment E. Coli colonizes the intestine by using the fimbriae to attach to each other and the cells lining of the intestinal track Biofilms! (plaque on teeth or scum in showers).
Pili Pili - usually longer than fimbriae and only one or two per cell. Facilitate transfer of DNA from one cell to another – join bacterial cells together. Sympathy for Bacteria
Glycocalyx (for protection & adherence): Capsules Only certain bacteria are capable of forming capsules (many pathogenic ones – like pneumonia) Chemical composition of each capsule is unique to the strain of bacteria that secreted it Capsules prevent phagocytosis (process of engulfing a microbe) by blocking the mechanism used by the white blood cell to attach. Slime Layer Less tightly bound to the cell wall and is usually thinner than a capsule Protects the cell against drying, traps nutrients and binds cells together (biofilm)
Pathogenicity: Adhesion Adhesion molecules on glycocalyx, pili, fimbriae, and flagella attach directly to host cell receptors Can form biofilms, very complex, many layers thick, resist disinfectants and antibiotics.
Slime Layer/Biofilm: Bacteria growing on tooth enamel
Prevents osmotic lysis (prevents cell rupture) Maintains cell shape Made of peptidoglycan (in bacteria) CLINICAL SIGNIFICANCE: Cell wall composition can contribute to the ability of the cell to cause disease Also the site of action for some antibiotics. Figure 4.6a, b
Components of Bacterial Cell Walls Peptidoglycan: The single most important component! This polymer is made up of two alternating sugar units: 1. N-acetylglucosamine (NAG) 2. N-acetylmuramic acid (NAM) The sugars are joined by short peptide chains that consist of four amino acids (tetrapeptides)
Figure 3.2 Units of Measurement 1 µm = 10 –6 m = 10 –3 mm 1 nm = 10 –9 m = 10 –6 mm 1000 nm = 1 µm 0.001 µm = 1 nm Generally, bacteria are measured in um and can be seen with a light microscope. Viruses are measured in nm and can only be seen with an electron microscope.
If a microbe measures 10 μm in length, how long is it in nanometers? 3-1
Microscopy: The Instruments 3-2Diagram the path of light through a compound microscope. 3-3Define total magnification and resolution.
Light Microscopy Use of any kind of microscope that uses visible light to observe specimens Types of light microscopy Compound light microscopy Darkfield microscopy Phase-contrast microscopy Differential interference contrast microscopy Fluorescence microscopy Confocal microscopy
Figure 3.1b Compound Light Microscopy In a compound microscope, the image from the objective lens is magnified again by the ocular lens Total magnification = objective lens ocular lens
Compound Light Microscopy Resolution is the ability of the lenses to distinguish two points A microscope with a resolving power of 0.4 nm can distinguish between two points ≥ 0.4 nm Shorter wavelengths of light provide greater resolution
Compound Light Microscopy The refractive index is a measure of the light-bending ability of a medium The light may bend in air so much that it misses the small high-magnification lens Immersion oil is used to keep light from bending
Figure 3.3 Refraction in the Compound Microscope
Many things can happen to light as it passes through a specimen on a slide. Reflection: If the light strikes an object and bounces back (giving the object color) Transmission: The passage of light through an object Absorption: The light rays neither pass through nor bounce off an object but are taken up by the object The more light that passes through the specimen (vs. lost), the higher the resolution
The bending of light as it passes from one medium to another of different density The bending of the light ray gives rise to an angle of refraction, the degree of bending Index of refraction: A measure of the speed at which light passes through the material Refraction
When two substances have a different index of refraction, the light is bent and is scattered When two substances have a similar index of refraction (diamonds and oil) then the light is not bent as it passes between the two substances
Refractive index is the light-bending ability of a medium. The light may bend in air so much that it misses the small high- magnification lens. Immersion oil is used to keep light from bending. Microscopy: The Instruments Figure 3.3
Through what lenses does light pass in a compound microscope? 3-2 What does it mean when a microscope has a resolution of 0.2 nm? 3-3
Uses electrons instead of light The shorter wavelength of electrons gives greater resolution ANIMATION Electron Microscopy Electron Microscopy
Figure 3.10a 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
Figure 3.10b 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