IMP

• Microorganisms


  Unicellular organisms that can be only seen by light microscope
• Eukaryotic cells


  Cells with a "true" nucleus enclosed in a nuclear membrane
• Bacteria


  Unicellular prokaryotic organisms that can be visualized by light microscope

  
• Viruses


  Made up of nucleic acid (either DNA or RNA) and protein, lack ribosomes so cannot generate energy, obligate intracellular parasites that can only replicate in association with a host cell
• Prokaryotes (microorganisms)


  • No membrane bound nucleus
  • No mitochondria
  • No other membrane bound organelles (endoplasmic reticulum, Golgi body, phagosomes, lysosomes)
• Microorganisms


  • Bacteria
  • Mycoplasma
  • Rickettsia
  • Chlamydia

  
• Bacterial morphology


  • Bacillus
  • Coccus
  • Spiral (spirilla and spirochetes)

  
• Bacterial arrangement


  • Diplo or chain when cleavage occurs in one plane
  • Grape-like clusters when cleavage occurs in all planes
• Bacterial size


  • 0.2-1.2um in diameter
  • 0.4-14um in length

  
• Differential stain


  Distinguishes between different types of bacteria
• Gram's stain


  Divides bacteria into gram positive (violet) and gram negative (red) based on cell wall structure

  
• Gram positive bacilli


  • Corynebacterium diphtheria (causes diphtheria)
• Gram negative cocci


  • Neisseria meningitidis (causes meningitis)
• Ziehl-Neelsen stain


  Identifies Mycobacteria (acid and alcohol fast) like M. tuberculosis, which have a waxy cell wall
• Bacterial motility


  Determined by observing living organisms

  
• Bacterial ultrastructures


  • Cytoplasmic region (nucleoid, ribosomes, inclusions, mesosomes)
  • Cell envelope (cell wall, plasma membrane, capsule/glycocalyx/slime layers)
  • Appendages (flagella, pili)

  
• Bacterial nucleoid


  Double-stranded DNA, 1 mm long, replicated in coordination with mesosomes during cell growth and division
• Bacterial ribosomes


  Site of protein synthesis
• Bacterial inclusions


  Energy reserves like glycogen, fat granules, and phosphate stored as volutin granules for ATP synthesis
• Bacterial mesosomes


  Folded invaginations in the cell membrane, support respiratory enzymes, involved in cell division and spore-formation

  
• Bacterial cell envelope


  Cell membrane where respiration occurs, surrounded by rigid cell wall to protect against osmotic lysis
• Gram negative cell envelope


  Additional outer membrane, periplasmic space between inner and outer membranes where degradative enzymes are stored
• Bacterial cytoplasmic membrane


  Thin elastic membrane surrounding the cytoplasm, made of two phospholipid layers

  
• Functions of bacterial cytoplasmic membrane

  • Selective transportation of nutrients
  • Respiration
  • Excretion of extracellular enzymes
  • Bacterial multiplication
  • Chemotactic system
• Bacterial cell wall


  Surrounds cytoplasmic membrane, provides shape, supports membrane, involved in multiplication, responsible for staining differences

  
• Peptidoglycan (PG)


  Basic structure of cell wall, resists lysozyme action
• Cell wall-deficient (CWD) bacteria


  1. forms produced when treated with antibiotics that interfere with peptidoglycan synthesis, Mycoplasma naturally lack cell wall

  
• Bacterial capsule and surface layers

  Composed of polysaccharide, not essential for viability, formed only in vivo, have functions like inhibiting phagocytosis, protecting cell wall, aiding attachment, resisting drying, storing nutrients and waste

  
• Bacterial flagella


  Responsible for motility, respond to chemical attractants and repellents (chemotaxis)
• Bacterial pili (fimbria)


  Hair-like projections that allow adhesion to host epithelial surfaces, some involved in sexual conjugation
• Bacterial endospores


  Resistant to adverse conditions, formed by some bacteria like Bacillus and Clostridium, have dehydrated cytoplasm, calcium dipicolinate, thick cortex and coat

  
• Bacterial spore formation


  Cytoplasmic membrane encloses part of cytoplasm containing chromosome and other materials, surrounded by thick cortex and coat

  
• Bacterial spore viability and resistance

  Resistant to disinfectants, heat up to 100°C, only killed by moist heat at 120°C for 20 min or 134°C for 10 min, stain red with modified Ziehl-Neelsen stain

  
• Bacterial spore germination


  Spores return to good nutritional conditions and produce a single vegetative cell
• Spore


  Bacterial structure that cannot be stained due to the presence of cortex and coat, stained by modified Ziehl-Neelsen stain and appear red
• Spore position


  Used for identification of bacteria, e.g. terminal in Cl. Tetani

  
• Spore germination


  When returned to good nutritional conditions, the spores germinate to produce a single vegetative cell
• Pili or Fimbria


  • Bacterial structure shown in Fig 6
• Endospore


  • Bacterial structure shown in Fig 7

  
• Bacterial requirements for growth include sources of energy and metal ions, optimal temperature, pH and the need or lack of oxygen