Chapter 4

• Microbiology


  The study of microbes
• Types of microbes


  • Acellular (viruses, virions, prions)
  • Cellular (bacteria, algae, archaea, protozoa, fungi)
• Cellular microorganisms


  • Eukaryotic (algae, protozoa, fungi)
  • Prokaryotic (bacteria, archaea)
• Virus replication


  Viruses must invade live host cells to replicate
• Some viruses, called oncogenic viruses or oncovirus, cause specific types of cancer
• Properties distinguishing viruses from living cells

  • Possess either DNA or RNA, unlike living cells which possess both
  • Unable to replicate on their own; replication is directed by viral nucleic acid in a host cell
  • Do not divide by binary fission, mitosis, or meiosis
  • Lack genes and enzymes for energy production
  • Depend on host cell for protein and nucleic acid production
• Classification of viruses


  • Type of genetic material, whether nucleic acid is single or double stranded, whether nucleic acid is positive or negative-sense, shape of capsid, number of capsomers, size of capsid, presence or absence of an envelope, type of host it infects, type of disease it produces, target cell, immunologic or antigenic properties
• Three major theories for the origin of viruses: coevolution theory, retrograde evolution theory, escaped gene theory
• Animal viruses collectively referred to as animal viruses infect humans and animals
• Steps in the Multiplication of Animal Viruses


  1. Attachment (absorption)

  2. Penetration

  3. Uncoating

  4. Biosynthesis

  5. Assembly

  6. Release
• Remnants or collection of viruses called inclusion bodies found in the cytoplasm
• Negri bodies are cytoplasmic inclusion bodies in nerve cells
• Latent virus infections are usually limited by the defense systems of the human body
• Viruses that cause cancer are called oncogenic viruses or oncovirus
• HIV, the cause of AIDS, is a member of the genus of virus called lentiviruses, in a family of viruses
• Ions are usually limited by the defense systems of the human body
• HIV, the cause of AIDS, is a member of the genus of virus called lentiviruses, in a family of viruses called Retroviridae (retrovirus)
• Antibiotics that function by inhibiting certain metabolic activities within prokaryotic and eukaryotic pathogens have no activity against viruses since they are not cells
• Drugs used to treat viral infections are called antiviral agents
• Bacteria can also be infected by viruses, called bacteriophages
• Categories of bacteriophages based on their shapes

  • Icosahedron bacteriophage: an almost spherical shape, with 20 triangular facets; Filamentous bacteriophages: long tubes formed by capsid proteins assembled into a helical structure; Complex bacteriophages: icosahedral heads attached to helical tails, may also possess base plates and tail fibers
• Categories of bacteriophages based on events

  • Virulent bacteriophage - always cause the lytic cycle; Temperate bacteriophage (lysogenic cycle) - do not immediately initiate the lytic cycle, but rather, their DNA remains integrated into the bacterial cell chromosome, generation to generation
• Steps in the Multiplication of Bacteriophage (Lytic Cycle)


  Attachment (absorption), Penetration, Biosynthesis, Assembly, Release
• Mimivirus can "mimic" bacteria
• Plant viruses are usually transmitted via insects, mites, nematodes, infected seeds, cuttings, and tubers, and contaminated tools
• Viroids consist of short, naked fragments of single-stranded RNA that can interfere with the metabolism of plant cells and stunt the growth of plants, sometimes killing the plants in the process
• Prions are small infectious proteins that cause fatal neurologic diseases in animals and humans in which the brain becomes riddled with holes
• Creutzfeldt-Jakob disease & Gerstmann-Straussler-Scheinker syndrome involve loss of coordination and dementia
• The Domain Bacteria contains organisms that are broadly divided into three phenotypic categories: Gram-positive, Gram-negative, those that lack a cell wall
• The three general shapes of bacteria are round (cocci), rod-shaped (bacilli), and spiral-shaped (sometimes referred to as spirilla)
• Cocci may be seen singly or in pairs (diplococci), chains (streptococci), clusters (staphylococci), packets of four (tetrads), or packets of eight (octads)
• Bacilli are often referred to as rods and may occur singly, in pairs (diplobacilli), in chains (streptobacilli), in long filaments, or branched
• Packets of bacteria


  • Four (tetrads)
  • Eight (octads)
• Bacilli


  • Often referred to as rods
  • May be short or long, thick or thin, and pointed or with curved or blunt ends
  • May occur singly, in pairs (diplobacilli), in chains (streptobacilli), in long filaments, or branched
• Staining Procedure


  1. Various staining methods devised to examine bacteria

  2. Fixation serves three purposes: 1. It kills the organisms 2. It preserves their morphology (shape) 3. It anchors the smear on the slide
• Simple Stain


  Sufficient to determine bacterial shape and morphologic arrangement
• Structural Staining Procedure


  Used to observe bacterial capsules, spores, and flagella
• Colony Morphology


  Bacterial colony is a mound or pile of bacteria on the surface of a solid culture medium
• Atmospheric Requirements


  1. Used to clarify bacteria based on their relationship to oxygen (O2) and carbon dioxide (CO2)

  2. Bacterial isolates can be classified into five major groups: obligate aerobes, microaerophilic aerobes, facultative anaerobes, aerotolerant anaerobes, obligate anaerobes
• Nutritional Requirements


  All bacteria need carbon, hydrogen, oxygen, sulfur, phosphorus, and nitrogen for growth