BACTERIAL METABOLISM, PHYLOGENY,BACTERIAL PATHOGENESIS

• Metabolism


  The sum of all chemical reactions required to support cellular function and hence the life of an organism

  
• Goals of metabolism


  • Energy transfer
  • Matter transport
  • Cellular work
  • Growth and reproduction

  
• Anabolism


  The constructive metabolism that builds up complex molecules from simpler ones
• Catabolism


  The destructive metabolism that breaks down complex molecules into simpler ones
• ATP


  Adenosine triphosphate
• Binary fission


  The process by which a bacterial cell divides into two daughter cells

  
• Generation time


  The length of time required for a single bacterial cell to yield two daughter cells (30 min to 20h)
• Specific environmental factors required for bacterial growth

  • Nutrients (e.g., glucose, nitrates, fatty acids)
  • pH
  • Ionic strength & osmotic pressure
  • Temperature
  • Gaseous requirement (oxygen, carbon dioxide)
• Nutrients are needed for energy production and as molecule sources
• Fermentation


  Anaerobic respiration producing 2-4 ATPs
• Aerobic respiration


  Respiration in the presence of oxygen producing more ATPs than fermentation
• Most pathogenic bacteria grow best at neutral pH (7.0). Some are acid tolerant and can survive the harsh conditions of the stomach.
• Most pathogenic bacteria grow best at osmotic pressures equivalent to physiological saline (0.65% NaCl).
• Most pathogenic bacteria are mesophiles (have an optimal temperature requirement for enzyme-catalyzed metabolic reactions)
• Bacterial oxygen requirements


  • Aerobes
  • Anaerobes
• The carbon dioxide is required for growth. The air levels are sufficient for many bacteria (0.04%). Some require elevated levels of carbon dioxide (5-10%).
• Bacterial growth


  The increase in the size of bacterial populations expressed as the number of cells present
• Bacterial growth curve


  • Increase in cell size, active metabolism of cells but no division
  • Cells multiply at maximum rate
  • Nutrient exhaustion & accumulation of toxic products
  • Progressive death of cells
• Spore formation can occur during the bacterial growth curve
• The result of bacterial (over)multiplication in the wrong place is disease
• Phylogeny


  The study of the evolutionary relationships among organisms
• Phylogenetic tree


  A diagram representing the evolutionary relationships among organisms, based on comparative gene sequence analyses of conserved genes (rRNA genes)
• Taxonomy


  The study of bacterial identification, nomenclature and classification
• Species


  The basic taxonomic unit, comprised of groups of strains that frequently exchange, or could exchange, core genes, but which are relatively restricted from such exchange with other groups
• Polyphasic taxonomy


  Classification of bacteria as evaluated by both genotypic, phylogenetic and phenotypic properties
• Bacterial pathogenesis


  The biological mechanisms that lead to a disease, or "how do bacteria cause disease?"
• Factors influencing disease


  • Susceptible host (breed, age, sex, genotype, physiology, immunity)
  • Environment (housing, management, hygiene, nutrition, disease control)
  • Pathogen (pathogenicity, virulence, infection route, tropism, inoculation dose, virulence factors)
• Obligate pathogen


  A pathogen that must infect a host and cause disease to multiply and be transmitted
• Facultative pathogen


  A pathogen that can infect and multiply in hosts but is also capable of multiplying in the environment
• Opportunistic pathogen


  A microorganism which does not ordinarily cause disease but which, under certain conditions (e.g., impaired host immunity) becomes pathogenic
• Host-pathogen interaction


  1. Exposure

  2. Adhesion

  3. Invasion

  4. Colonization
• Potential outcomes of host-pathogen interaction include commensal interaction, mutualistic relationship, or disease
• Stages of bacterial infection

  1. Exposure

  2. Adhesion

  3. Invasion

  4. Colonization
• Possible infection outcomes


  • No colonization
  • Infection → disease → recovery
  • Infection → subclinical disease
  • Infection → disease → death/disability
  • Infection → disease → persistence (carriers)
• Inflammation


  The biological host response to harmful stimuli such as pathogens and/or their metabolites, characterized by redness, swelling, heat and pain
• Inflammation can result in local tissue damage, toxemia, acute systemic disease, or chronic disease
• Subclinical disease


  Mild illness that is part of the "iceberg" of disease, with severe diseases and death being the visible tip