Module 1: Introduction to microbiology

Naming of bacteria

• established in 1735

• Two names: genus & specific epithet

• Honor a scientist or identify a habitat

• Genus capitalized, specific epithet lower case

The first microscope`

Made by Van Leeuwenhoek; x300, only one lens

Compound light microscopy

• Image from the lens is magnified again by the ocular lens

• Total magnification = objective lens x ocular lens

• Resolution; ability to distinguish two points, shorter wavelenghts of light provide greater resolution

• Refractive light; light-bending ability of medium, staining changes refractive index of specimen/ increase images contrast, immersion oil keeps light from bending in air

Brightfield microscope

• visable light as source of illuminations

• for various stained organisms

  • can’t see <0.2μm

Darkfeild

• uses special condenser with opaque disk

• only light reflected off the specimen enters the objective lens

• used to veiw microbes invisible in brightfiels or unstainable

Phase-Contrast Microscopy

• light passes through ring diagram

• splits into 2 sets of rays

• accentuants diffraction of the light that passes through a specimen

• no stain needed

Differential interference contrast microscopy

• light passes though prism

• split into 2 beams of light

• no need to stain

Fluorescence microscopy

• uses UV light

• cells are stained with fluorescent dyes

• fluorescent substances absorb UV light and emit visable light

• Useful for identifying microbes in clinical samples

Confocal microscopy

• Uses laser light and fluorescent dyes

• laser illuminates each plane in a specimen to produce a 3-D image

Scanning acoustic Microscopy (SAM)

• Measures sound waves reflected back from an object

Electron microscopy

• Uses electrons instead of light

• ultrathin sections of specimins are seen

• Greater resolution

• TEM, SEM

Transmission Electrom Microscopy (TEM)

• Specimins may be stained with heavy metal salts

• examine different layers of specimen

Scannine electron microscopy (SEM)

• Scans surface of a whole specimen

• Magnification 1000-10000x

• 3-D picture

Gram staining steps

1- primary stain; Crystal violet

2- Mordant; Iodine

3- Decolorizing agent; Alcohol-acetone

4- Counterstain; Safranin

Gram-positive color

Purple

Gram-negative color

Pink

Eukaryotes

• Complax

• Simple polysaccharide in cell wall

• Multiple chromosomes

• True membrane bound organelles

• Mitosis

• Histones present

• No antibiotic sensitivity

Prokaryotes

• Simple

• Complex peptidoglycan cell wall

• Single chomosome

• No true nucleus

• No membrane bound organelles

• Binary fission

• No histones

• Antibiotic sensitivity

Glycocalyx

• sugar coat

• external to cell wall

• also called capsule

• identified through negitive staining

• protects against phagocytosis and dehydration

Flagella

• Long filamentous appendage

• Organ of movement

• filament - hook - basal body

• attract or repel from stimuli

• more complex in eukaryotes than prokaryotes

• carry H antigens

Axial filaments

• also known as endo-flagellae

• fibrils are anchored to one end, located beneath the sheath, siral, and move in a spiral fashion

Fimbriae

• hair- like appendages

• few to sevral hundrend on a single bacterial cell

  • allow attachment/colonization to mucous membranes

Pili

• large

• 1-2/ cell

• used to transfer DNA from one cell to another

bacterial cell wall

• complex, rigid structure surrounding bacteria

• maintain cell shape

• anchorage to flagella

• protects interior of cell

• prevents osmotic lysis

• made of peptidoglycan

peptidoglycan

macromolecular network formed by repeated disaccharides, linked by polypeptides

gram-positive cell wall

• thick peptidoglycan

• contains teichoic acids

• no outer membrane

Gram-negative cell wall

• thin peptidoglycan

• No teichoic acids

• outer membrane

Acid-fast stain mechanism

• acid-fast bacteria contain mycolic acid

• carbolfuchsin (primary red stain) penetrates cell wall & binds to cytoplasm