Micro

• Culturing Virions


  Growing viruses in the laboratory

  
• Culturing of Microbes


  1. Growing bacteria on agar

  2. Some are intracellular parasites which would need eukaryotic cells (Rickettsia)

  3. Fungi can grow on agar (high sugar)

  4. Virions require cells to replicate because they are intracellular parasites
• Epidemiology


  The study of the frequency and distribution of disease and other health-related factors in defined human populations
• Figure 13.9 shows the pattern of virion abundance in lytic cycle
• Disciplines involved in epidemiology

  • Microbiology
  • Anatomy
  • Physiology
  • Immunology
  • Medicine
  • Ecology
  • Psychology
  • Sociology
  • Statistics
• Culturing Virions in Bacteria

  1. Phages grown in bacteria in liquid cultures or on agar plates

  2. Lysis of bacteria produces plaques

  3. Allows estimation of phage numbers by plaque assay
• Culturing Virions in Plants and Animals

  1. Numerous plants and animals have been used to culture virions

  2. Laboratory animals can be difficult and expensive to maintain

  3. Ethical concerns
• Robert Koch's standard for determining the etiologic agent

  • The suspected causative agent must be found in every case of the disease and be absent from healthy hosts
  • The agent must be isolated and grown outside the host
  • When the agent is introduced into a healthy, susceptible host, the host must get the disease
  • The same agent must be re-isolated from the diseased experimental host
• Paul Ehrlich


  Father of Chemotherapy
• Culturing Virions in Embryonated Chicken Eggs

  1. Inexpensive

  2. Fertilized chicken eggs are often used

  3. Embryonic tissues provide ideal site for cultivating virions

  4. Some vaccines prepared in chicken cultures
• Stanley Falkow's Molecular Postulates

  • The phenotype or characteristic in question should be associated with all pathogenic members of a genus or pathogenic strains of a species and absent from non-pathogenic strains
  • Inactivation of the suspected virulence gene(s) should result in a reduction in pathogenicity or virulence which can be measured in an animal model
  • Reversion or allelic replacement of the mutated gene should lead to restoration of pathogenicity
• Paul Ehrlich's discoveries


  • Discovered the first antibiotic "salvarsan" in 1907
  • Arsenic derivative effective against trypanosome and Treponema pallidum
  • Nasty side effects like liver damage, rashes and possible death
  • Replaced mercury and iodine for effectiveness
  • Nobel Prize in 1908 for immunology
• Cell Culture


  • Cells isolated from an organism and grown on a medium or in a broth
  • Primary cell cultures
  • Continuous cell cultures
• Selective toxicity concept


  Only targets the pathogen without harming the patient
• Epidemic


  A sudden acute disease outbreak affecting many people
• Viral Replication


  The process by which viruses replicate and reproduce inside the living cells of other organisms

  
• Magic bullets


  Targeted the pathogen and killed with a toxin
• Bacteriophage


  A virus that infects and replicates within bacteria

  
• Pandemic


  A worldwide epidemic (across geopolitical boundaries)
• Virions


  • Have different "tropisms"
  • Hosts and host cells
  • Bacteriophage need bacteria, animals virions need animal cells even the correct species
• Monoclonal antibodies (Mabs)


  • Conjugated to toxins
• Replication of Animal Viruses

  • Same basic replication pathway as bacteriophages
  • Differences result from presence of envelope around some viruses
  • Eukaryotic nature of animal cells
  • Lack of cell wall in animal cells
  • Nucleocapsid always enters the cell

  
• Endemic


  Chronic occurrence of a disease in a geographical region
• Alexander Fleming


  • Discovered penicillin released from Penicillium
  • Shared 1945 Nobel Prize

  
• Primary organs of the lymphatic system

  • Bone marrow
  • Thymus
• Pattern of virion abundance

  • Lytic cycle
  • Persistent infections

  
• Most of our knowledge of virions has been learned in the last 60 years
• Sporadic


  Random small outbreaks of a disease
• Gerhard Domagk


  • Discovered sulfanilamide
  • 1939 Nobel Prize
• Secondary organs of the lymphatic system

  • Tonsils/adenoid
  • Spleen
  • Lymph nodes
  • Appendix
  • Mucosal associated lymphatic tissue (MALT)
• Selman Waksman


  • Discovered over 20 antibiotics
  • Coined the term antibiotic
  • 1952 Nobel Prize
• Types of epidemics


  • Common-source
  • Point source
  • Propagated source
• Pluripotent hematopoietic stem cells


  The source of blood cells found in the bone marrow
• Assembly and release of animal viruses

  1. Many DNA viruses assemble in nucleus

  2. Most RNA viruses develop solely in cytoplasm

  3. Enveloped viruses cause persistent infections

  4. Naked viruses are released by exocytosis or lysis

  
• Mechanisms of action of antimicrobial drugs

  • Inhibition of cell wall synthesis
  • Inhibition of pathogen's attachment or entry into host cell
  • Inhibition of DNA or RNA synthesis
  • Inhibition of general metabolic pathway
  • Disruption of cytoplasmic membrane
  • Inhibition of protein synthesis
• Blood cells derived from pluripotent hematopoietic stem cells


  • White blood cells
  • Red blood cells
  • Platelets
• DNA Viral Replication


  1. dsDNA viruses use host DNA polymerase and viral genome is replicated in the nucleus, using RNA machinery of the host

  2. Viral proteins are made in the cytoplasm

  3. Hepatitis B uses an RNA intermediary and reverse transcriptase

  4. Poxvirus replication occurs in the cytoplasm and requires DNA polymerase

  
• Morbidity rate


  The number of persons afflicted with infectious diseases
• Virions


  • Extracellular state of viruses
  • Includes nucleic acid, capsid, and sometimes envelope

  
• Examples of antimicrobial agents for each mechanism


  • Penicillins, Carbapenems, Cephalosporins, Vancomycin, Bacitracin, Isoniazid, Ethambutol, Echinocandins (antifungal)
  • Arildone, Pleconaril, Enfuvirtide
  • Actinomycin, Nucleotide analogs, Quinolones, Rifampin
  • Sulfonamides, Trimethoprim, Dapsone
  • Polymyxins, Polyenes (antifungal)
  • Aminoglycosides, Tetracyclines, Chloramphenicol, Macrolides, Antisense nucleic acids