Chapter 4

• Acellular microbes


  Microbes that are not truly cellular, including viruses, viroids, and prions
• Cellular microbes (microorganisms)


  Microbes that are truly cellular, including bacteria, archaea, algae, protozoa, and fungi
• Prokaryotic microbes


  Cellular microbes that are bacteria and archaea
• Eukaryotic microbes


  Cellular microbes that are algae, protozoa, and fungi
• Viruses


  • They possess either DNA or RNA, whereas living cells possess both
  • They are unable to replicate on their own
  • They do not divide by binary fission, mitosis, or meiosis
  • They lack the genes and enzymes necessary for energy production
  • They depend on the ribosomes, enzymes, and metabolites of the host cell for protein and nucleic acid production
• Virion


  Complete virus particle
• Viruses


  • Most range from 10 to 300 nm in diameter
  • They infect humans, animals, plants, fungi, protozoa, algae, and bacterial cells
• Oncogenic viruses (oncoviruses)


  Viruses that cause specific types of cancer
• Capsid


  Protein coat surrounding a virus genome
• Capsomeres


  Protein units that make up a virus capsid
• Enveloped viruses


  Viruses with an outer envelope composed of lipids and polysaccharides
• Types of viral genomes

  • Double-stranded DNA viruses
  • Single-stranded RNA viruses
  • Single-stranded DNA viruses
  • Double-stranded RNA viruses
• Multiplication of animal viruses

  1. Attachment

  2. Penetration

  3. Uncoating

  4. Biosynthesis

  5. Assembly
• Latent virus infections


  Viral infections where the virus hides from the host's immune system by entering cells and remaining dormant
• Oncogenic viruses (oncoviruses)


  Viruses that cause cancer, including Epstein-Barr virus, human papillomaviruses, and human T-lymphotrophic virus type 1 (HTLV-1)
• Human immunodeficiency virus (HIV)


  Enveloped, single-stranded RNA virus that causes acquired immunodeficiency syndrome (AIDS)
• Antiviral agents


  Drugs used to treat viral infections that interfere with virus-specific enzymes and virus production
• Bacteriophages


  Viruses that infect bacteria
• Virulent bacteriophages


  Bacteriophages that always cause the lytic cycle, ending in destruction of the bacterial cell
• Lytic cycle of virulent bacteriophages

  1. Attachment

  2. Penetration

  3. Biosynthesis

  4. Assembly

  5. Release
• Viroids


  Short, naked fragments of single-stranded RNA that can interfere with the metabolism of plant cells
• Prions


  Small infectious proteins that cause fatal neurologic diseases in animals and humans called transmissible spongiform encephalopathies
• Phenotypic categories of bacteria

  • Gram-negative with cell wall
  • Gram-positive with cell wall
  • Lack cell wall (Mycoplasma spp.)
• Characteristics used to classify and identify bacteria

  • Cell morphology
  • Staining reactions
  • Motility
  • Colony morphology
  • Atmospheric requirements
  • Nutritional requirements
  • Biochemical and metabolic activities
  • Enzymes produced
  • Pathogenicity
  • Genetic composition
• Cocci


  Round bacteria
• Bacilli


  Rod-shaped bacteria
• Coccobacilli


  Extremely short bacilli
• Vibrio spp.


  Curved bacteria
• Campylobacter spp.


  Curved bacteria
• Helicobacter spp.


  Curved bacteria
• Treponema spp.


  Spiral-shaped bacteria
• Borrelia spp.


  Spiral-shaped bacteria
• Staining procedures for bacteria

  • Simple staining
  • Structural staining (capsule, spore, flagella)
  • Differential staining (Gram, acid-fast)
• Heat fixation


  Technique for fixing bacterial smears, but can distort morphology
• Methanol fixation


  Standardized technique for fixing bacterial smears
• Gram staining


  Divides bacteria into Gram-positive (blue/purple) and Gram-negative (pink/red)
• Gram-positive bacteria


  Have a thick layer of peptidoglycan in their cell wall
• Gram-negative bacteria


  Have a thin layer of peptidoglycan in their cell wall
• Bacterial smears


  Must be fixed prior to staining
• Fixation process


  Serves to kill organisms, preserve their morphology, and anchor the smear to the slide