Week 1

• Prokaryote


  • unicellular
  • no membrane-bound organelles/nucleus
  • divide by binary fission
  • genetic material typically single, haploid, circular chromosome
• Eukaryote


  • multicellular
  • membrane-bound organelles and nucleus
  • divide by mitosis/meiosis
  • genetic material in chromosomes
• Gram positive


  thick cell wall of peptidoglycan, made of NAG and NAM
• Gram negative


  thin cell wall, extra outer membrane with LPS

  
• gram stain

  Stains peptidoglycan of the cell wall purple
• Acid Fast


  Stains mycolic acid in cell envelope
• Flagella


  • Aid motility and adherence
• Pili/fimrae/adhesins


  • Aid motility and adherence
• Capsule


  • Aid motility and adherence
• Spirochetes have endoflagella in periplasmic space
• Common Virulence Factors


  • Endospores
  • Flagella
  • Pili/fimrae/adhesins
  • Capsule
• Endospores


  • Nutrient reserve, protection from phagocytosis
  • Cryptobiotic state of dormancy
  • Can produce toxins during germination/sporulation (ie: Clostridium and Bacillus)

  
• Endotoxins


  Produced by the bacteria, highly antigenic

  Have specific targets/effects

  
• Secretion systems


  The way bacteria introduce proteins to the host cells
• Biofilm


  • Clusters attached to a surface in a self-produced matrix. Contain proteins, polysaccharides, and released DNA
  • Protective organization, often using quorum sensing

  
• Quorum sensing


  • Cell-cell communication using signal molecules
  • Once a defined density is reached, pheromone concentration signals expression of genes that make the colony act as a unit
• Transfer of virulence factors


  1. Horizontal transfer of genetic material (this is a major cause of resistance)

  2. Transformation: free release and capture

  3. Transduction: using a phage

  4. Conjugation: using pilus (think conjugal visits)
• Bacterial Growth


  1. Lag phase

  2. Exponential growth phase

  3. Stationary phase (max capacity)

  4. Decline (death)
• Bacterial Growth Factors


  • nutrients
  • pH
  • temperature
  • gaseous requirements (O2, CO2)
  • Osmotic pressure/ionic strength

  
• Types of pathogens


  • Obligate
  • Primary
  • Opportunistic
  • Non-pathogenic
  • Saprophyte
• Virulent


  causing disease; virulence: level of severity of disease
• Intra/extracellular


  most are extracellular; some species may be obligate or facultative intracellular
• Host-Pathogen Interactions


  1. have a susceptible host and environment within it - exposure

  2. compete with microbiota and adhere to host cells - adhesion

  3. overcome host defenses - invasion and colonization

  4. express virulence factors that cause disease - toxicity and tissue damage
• Outcomes of infection


  • healthy
  • Elimination via immune system
  • Subclinical infection
  • Clinical disease
• Diagnostics Phases


  • Pre-analytical: test selection, sample collection, storage, and transport
  • Analytical: detection of agent or immune response, sample processing in the lab
  • Post-analytical: interpretation of results, treatment plan
• Gold standard: culture isolation and identification.
• Culture medium types


  • General purpose media (ex: TSA)
  • Selective media: only certain kinds will grow (ex: PEA, MacConkey, SDA)
  • Differential media: certain bacteria cause change in agar (ex: MacConkey differentiates lactose fermentation, Blood Agar differentiates on hemolysis)
• Detection of Antigen


  • Direct microscopy
  • Antigen detection (FAS, ELISA, agglutination)
  • Molecular techniques (PCR/rtPCR)
• MacConkey Agar


  Selective for Gram negs, and differential for lactose fermentation
• The bacteria on the left are Gram negative and DO ferment lactose
• The bacteria on the right are Gram negative and do NOT ferment lactose
• Antibody titer


  expressed as highest dilution with a positive reaction (ex: titer of 50 means it took a dilution of 1:50 to stop testing positive)
• Seroconversion


  a four-fold increase in Ab titer 2 weeks apart means antibody development occurred after exposure (evidence of infection)
• Other humoral testing methods


  • ELISA
  • immunofluorescence
  • precipitation
  • agglutination
• Humoral response serology


  Pros: Rapid tests available, useful for screening

  Cons: False positives and false negatives
• Tuberculin skin test


  Tests for Mycobacterium bovis

  Procedure: Day 1: Two injections - M. bovis and M. avium (control)

  Day 4: check site - if over 4mm reaction animal is positive
• Interferon Gamma test


  Whole blood test for Mycobacterium group, results in 24h
• Antimicrobials


  Any substance of natural, semisynthetic, or synthetic origin that either kills microbes or prevents their multiplication. (Includes: antibiotics, antivirals, antiparasitics, and antifungals)
• Bactericidal


  kills bacteria and reduce total number
• Bacteriostatic


  inhibits bacterial growth and replication, allowing the host immune system to catch up