Lecture 5

• Pathogen

  always causes infection (ebola virus, neisseria gonerrhea), never colonizes
• Potential pathogen

  does not always lead to infection but always has the possibility to. Needs to be right place and right time (e. coli, MRSA)
• Non-pathogen

  most organisms can cause infection in the right setting, these normally DO NOT cause one except in very RARE situations (lactobacillus in soft cheeses and yogurt)
• Virulence factors

  factors that help organisms infect or avoid immune responses (capsule, toxic secretion)
• normal flora/microbiota


  organisms that are normally fond at certain body sites (can cause disease if found in other places on body)
• Mucosal membranes


  surfaces that are lined with mucus are have bacteria that are present

  *bacterial are in all ecological niches (mouth, nose, genital tract, GI tract)

  BUT, this is also entry points for potential pathogens
• Skin flora

  colonized by gram positive bacteria above the gut (staphylococci, bacilli and cocci). below the gut is gram negative (focuses on how we wash)

  *can cause infectious colonies (staphylococcus aureus) but most common one is coagulase negative staphyloocci predominate
• Respiratory tract flora


  colonized by around 1,000,000,000 bacteria/mL. determined by oral flora. Most of the time lungs are sterile. Teeth are main collectors of bacteria, why babies has good breath before teeth grow in
• Gastrointestinal tract flora


  is dependent on location (upper or lower tract?). Upper tract has facultative aerobes. Lower tract has anarobes (only grows without oxygen). few gram positive organisms, mostly enterococci
• genitourinary tract

  urine keeps this clean (sterile bladder). vaginal flora changes with age (pH lowers with puberty and menopause). women of child bearing age has more bacteria (main being lactobacillus)
• Upsetting the normal flora

  normal flora is here to help protect us, if we disturb it, we are at risk of catching something. Stops colonization of things. Things like C. difficile can get worse with antibiotics so it is up to flora
• C. difficile


  makes spores that are stable in environment allowing it to spread. Can make toxins in kids that are deadly or cause big infection in colon. main cause of antibiotic related diarrhea. Causes changes in GI flora. Paired with ulcerative clotitis
• Genital flora


  disruptions in microbiota of vaginal tract can is associated with bacterial vaginosis
• Non-specific host defense?

  non-specific non innume host defence. Barriers are natural non-specific (structures, pH, enzymatic), works with normal flora to prevent infections and protect against pathogens
• Non-specific host responses


  first line of defence that immune system sends (innate responses)
• types of non-specific host responses

  Urination washes urethra to keep sterile bladder.

  mucociliary elevator: ciliated cells move material towards larynx to be swallowed and removed by digestive system (or towards mouth/nose to be released there).

  Lysozyme: breaks peptidoglycan to destroy cells

  lactoferrin: binds free iron and limits bacterial from collecting it

  Secretory IgA: antibodies secretion (Saliva)

  Inflammation and cellular recruitment to site of damage (Neutrophils and ROS (toxic to cells)
• What does damaged cites do?

  sends out signals to immune system to get help

  
• Innate (nonspecific) immunity?


  first line of defenses

  • skin
  • mucous membranes
  • secretions
  • reflexes
  • Normal microbiota

  Second line of defense

  • inflammation
  • phagocytes
  • Fever
  • Complement system
  • interferon
• Acquired (specific) immunity


  special responses to special danger. Third line of defense:

  • T cell lymphocytes
  • B cell lymphocytes
  • Antibodies

  *takes a couple weeks
• Innate immunity


  rapid response, no memory
• Adaptive immunity


  initial slow response, subsequent rapid response and long term memory (once developed, will stay in blood to make response quicker next time it is needed)
• Innate immune system

  inflammatory response, cellular recruitment to site of infection.

  phagocytosis (eats bacteria, puts into vacuoles/pockets, and either absorbs or releases parts after)
• Humoral response or antibody-mediated response

  Humoral = Immunoglobulins (antibodies). These respond to antigens (Anti -> antibody; gen -> generator)

  • IgG (transferable from mom to baby, lasts 6months-30 years)
  • IgM (early body response)
  • IgA
  • IgE
  • IgD

  precipitate, agglutinate promote factors that help immunoglobulins
• Cell-mediated immunity


  *only kills own body cells that are infected

  Important as a defence in combination with antibody but may also be important alone
• Types of cell-mediated immunity?

  Regulatory T cells, T-cells, Cytotoxic, natural killer cells (kills body cells that do not behave properly)

  
• Cytotoxic T cells


  destroy changed cells by noticing different protein sequences on the cell surface
• Cytotoxic cells


  detect changes in the types of peptides shown on the cell. Expand into large population of clones and then will contract once the pathogen has been cleared. Small proportion o fcells will become memory cells
• Memory cells


  immune response that once they attack a specific antigen so if that antigen comes back, it will remember it and start attacking it again quicker than last time