Introduction

• Prokaryotic


  Single-celled, microscopic organisms
• Three basic shapes of bacteria

  • Coccus (spherical)
  • Bacillus (rod)
  • Spirillum (spiral)

  
• Other bacterial shapes


  • Sheath
  • Stalked
  • Filamentous
  • Square
  • Star-shaped
  • Spindle-shaped
  • Lobed
  • Trichome-forming
  • Pleomorphic

  
• Cell morphology


  Cell shape and arrangement
• Cell morphology


  • 3 major cell morphologies
  • Few unusual shapes
  • Many variations on basic morphological types – not solely on morphology
• Coccus


  Spherical cell shape

  
• Coccus arrangements


  • Diplococcus (pairs)
  • Streptococcus (chains)
  • Tetrad (squares of 4)
  • Sarcina (cubes of 8)
  • Staphylococcus (irregular grape-like clusters)

  
• Bacillus/Rod


  Rod-shaped cell
• Bacillus/Rod arrangements


  • Bacillus (single)
  • Streptobacillus (chains)
  • Coccobacillus (oval)
• Spiral


  Spiral-shaped cell
• Spiral arrangements


  • Vibrio (curved or comma-shaped rod)
  • Spirillum (thick and rigid spiral)
  • Spirochete (thin and flexible spiral)
• Microorganisms


  • E.coli
  • Giardia lamblia
  • Plant cell
  • Budding yeast cell
  • Red blood cell
  • Fibroblast cell
  • Eukaryotic nerve cell
  • Rod cell from the retina
• Prokaryote size


  0.2 to >700 µm in diameter
• Eukaryote size


  10 to >200 µm
• Typical rod-shaped bacteria size

  0.5 to 4 µm wide; <15 µm long

  
• Large prokaryotes


  • Epulopiscium fishelsoni (contains multiple copies of genome)
  • Thiomargarita namibiensis (store inclusions of sulfur)
• Significance of small cell size

  • Less energy requirements
  • Does not need to 'hunt'
  • Easier transportation of metabolites
  • Survive at low level of substrates – autotrophs (sunlight or chemical reactions)
• Three selective pressures on cell size and shape

  • Nutrient acquisition – shape is physical response
  • Motility – solid surface vs viscous fluids
  • Predators – escaping the shape of 'just right'
• Caulobacter crescentus


  • Stalked bacteria

  
• Gram staining


  Differential stains used to characterize bacteria into Gram-positive (purple) and Gram-negative (red) groups
• Gram staining is a major approach highly used to differentiate bacteria
• Bright-field microscopy


  Uses visible light to illuminate cells
• Types of light microscopy

  • Bright-field
  • Phase-contrast
  • Dark-field
  • Fluorescence
• Principles of light microscopy

  • Magnification – ability to make an object larger
  • Resolution – ability to distinguish two adjacent objects as separate and distinct
  • Staining improves contrast for observations
• Phase-contrast microscopy


  Improves contrast without staining
• Dark-field microscopy


  Movement of light makes dark background
• Fluorescence microscopy


  Cells fluoresce naturally or are stained with dye, DAPI; widely used for bacterial enumeration

  
• Differential interference contrast (DIC) microscopy

  Uses polarizer to create two distinct beams, emphasizes cellular structures like endospores, vacuoles, and granules
• Confocal scanning laser microscopy

  Able to focus the laser on single layers of the specimen, create multiple layers that can be compiled, smallest resolution of 0.1 µm
• Electron microscopy


  Uses a beam of electrons instead of light, produces higher-resolution images
• Types of electron microscopy

  • Scanning electron microscopy (SEM)
  • Transmission electron microscopy (TEM)
• Scanning electron microscopy (SEM)

  Specimen is coated with a thin film of heavy metal, electron beam scans the object and scattered electrons are collected by a detector, image magnification of 15× to 100,000×
• Transmission electron microscopy (TEM)


  Electromagnets function as lenses, allows high magnification and resolution, visualization at molecular level
• Microorganisms


  Microscopic living organisms
• Robert Hooke


  • Built his microscope in 1655
  • Illustrated the fruiting structures of molds
  • Introduced the word 'cells'
• Anton van Leeuwenhoek


  • Made single-high quality lens
  • First person to discover bacteria
  • Described red blood cells in 1676
• Ferdinand Cohn


  • Discovered that some bacteria formed endospores
  • Described the life-cycle of the endospore-forming bacterium Bacillus
  • Laid groundwork for a system of bacterial classification
  • Devised effective methods for preventing contamination of culture media
• Bacterial cell shapes


  • Circular (Coccus)
  • Rod-shaped (Bacillus)
  • Curved Forms
  • Diplo- (in pairs)
  • Coccobacilli (oval)
  • Vibrio (curved rod)
  • Helicobacter (helical)
  • Strepto- (in chains)
  • Streptobacilli
  • Spirilla (coil)
  • Corynebacterium (club)
  • Staphylo- (in clusters)
  • Mycobacteria
  • Spirochete (spiral)
  • Streptomyces (filaments)
• Louis Pasteur


  • Refuted spontaneous generation theory - swan-necked flasks
  • Developed vaccines – anthrax, rabies, smallpox and cholera
• Pasteurization, ultra-pasteurization, and homogenization

  1. High temperature short time - 72°C for 15 s

  2. Ultra-pasteurization - Raw milk is heated to 280 degrees for approximately 4-5 seconds

  3. High temperature pasteurization - Raw milk is heated to 161 degrees for 15 seconds, and then rapidly cooled

  4. Low temperature pasteurization - Raw milk is heated 145°F for 30 minutes and then rapidly cooled

  5. Raw Products - Have not been heat treated to kill off any harmful bacteria