Bacterial Pathogenesis

  1. what are strict "true" pathogens
    • must infect a host organism as part or all of their life cycle
    • can cause disease in healthy individuals with competent immune systems
    • are typically associated with specific diseases (anthrax, syphilis, plague)
  2. what are opportunistic pathogens
    do not require a host for survival but can infect a host in immunocompromized individuals or disrupted healthy microbiomes
  3. what are three examples of opportunistic bacteria that are part of the healthy microbiome
    • staphylococcus spp
    • clostridium dificile
    • e. coli
  4. what are some examples of opportunists that are from the environment
    • pseudomonas aeruginosa: usually infects burn victims
    • vibrio cholerae
    • clostridium tetani
  5. what are virulent bacteria
    promotes their own growth within a host at the expense of the host's tissue or organ function, causing disease
  6. what are virulence factors
    molecules and structures of both strict and opportunistic pathogens that allow organisms to infect a host
  7. what are mobile genetic elements
    • virulence factors from bacteria that transfers to another bacteria
    • located in pathogencitiy islands and plasmids
  8. what are avirulent bacteria
    • bacteria that are unable to infect a  host
    • may be caused by mutations
  9. what is the difference between virulent and avirulent strains of streptococcus pneumoniae
    • virulent: smooth, contains a polysaccharide capsule.
    • avirulent: rough, no capsule
  10. what are pathogenicity islands
    • mobile genetic elements
    • large chromosomal regions containing sets of genes that encode virulence factors. Contains repetitive sequences that allow the entire region to move within a chromosome or between organisms by horizontal gene transfer
  11. what are plasmids
    • a mobile genetic element
    • can be transferred between bacteria through conjugation
  12. what are the environmental factors that influence the movement of pathogenicity islands and plasmids between bacteria
    • low pH (stomach acid)
    • temperature
    • oxidative stress (reaction to immune system cells)
  13. describe the immune response that bacteria cause
    • inflammatory immune response: body recruits immune cells to site of bacterial invasion in response to eradicating invaders
    • includes redness, swelling (edema), heat (release of pyrogens or fever agents), pain
  14. what happens the longer the bacterium remains in the body
    • the greater the bacteria proliferates, the greater its ability to spread and its potential to cause tissue damage and disease.
    • it also causes a larger host reponse
  15. how does bacterial load affect disease
    • the inoculum size and bacterial strain affect the onset of disease.
    • different numbers of bacteria are required to initiate infection depending on the strain
    • ex) 200 cells of shigella required to induce shigellosis, 10^8 cells of vibrio cholerae required to cause GI tract infection
  16. how can host factors affect disease
    • changes in host resistance: whether the host is already immunocompromized, nutritional deprivation, obseity, pregnant
    • external factors: trauma, medical treatment, overuse of antibiotics
    • modification of healthy host microbiome
  17. how do antibiotics affect drug resistant bacteria
    • in a group, some bacteria are already drug resistant
    • when antibiotics kill the bacteria causing the illness, it leaves some of the drug resistant bacteria
    • the drug resistant bacteria then proliferate and can transfer their resistance to other bacteria, causing more problems
    • presence of antibiotics puts selective pressure on bacterial cells to acquire antibiotic resistance
  18. how do bacteria enter a host to cause infection
    • tears in skin
    • tumor or ulcer in bowel
    • internal wound
    • sexual transmission
    • bug bite
    • inhalation
    • trauma
    • injestion
  19. what are the host's natural defenses against bacterial entry
    • skin
    • mucous membranes
    • ciliated epithelium
    • secretions containing antibacterial substances
  20. how do bacterial adhere to host tissue (4)
    • adhesins
    • pili
    • biofilms
    • capsules
  21. what are adhesins
    molecules on surface of cells that bind to receptors on host tissue and keep bacteria from being washed away
  22. what are pili
    projections from bacterial cells that often have adhesins on their ends and keep bacteria anchored to host tissues
  23. what are biofilms
    • sticky matrix of polysaccharides, proteins, and nucleic acids that bind bacterial cells together and to surfaces.
    • f(x): protects bacteria from host defenses and antibiotics
  24. what are capsules
    slime layer around the outside of cells that help bacteria stick to host cells and evade immune detection
  25. what are some adherence factors (7)
    • ligand
    • adhesin
    • lectin
    • S-layer
    • capsule
    • lipopolysaccharide
    • lipoteichoic acid
  26. what is an S-layer
    • a proteinaceous layer forming the outermost structure of the cell envelope of some bacteria
    • f(x): faciliates adhesion, colonization, and immune evasion
  27. what are lipopolysaccharides
    • on the outermost part of the outer membrane of G (-) bacteria. May faciliate adherence to host tissues
    • can be a PAMP as an endotoxin
  28. what is lipoteichoic acid
    • cell wall component of G(+) bacteria that may facilitate adherence to host tissues 
    • may be recognized by host immune system as a PAMP
  29. what are teichoic acids
    • species specific polymers covalently attached to the cell wall of G(+) bacteria
    • lipoteichoic acids (LTAs) are bound to cell membrane
  30. what are functions of wall teichoic acids and lipoteichoic acids
    • directing cell division machinery
    • shape molecular surface properties (allows sticking to surfaces)
    • mediating biofilm formation
    • serving as phage receptors
    • mediating interactions with host receptors
    • controlling susceptibility and/or resistance to antibiotics
  31. how do bacteria spread into deeper host tissues
    using factors such as invasins that include spreading factors and enzymes to facilitate the spread of bacteria
  32. what are spreading factors (invasins) by bacteria that affect the physical integrity of tissue matrices and intercellular spaces and their f(x) (3)
    • hyaluronidase: degrades hyaluronic acid found in connective tissue
    • collagenase: breaks down collagen
    • neuramidase: degrades neuraminic acid (coats mucous layer in gut)
  33. what are the enzymes (invasins) used by bacteria that directly cause host cells to lyse
    • phospholipiases: hydrolyze phospholipids in cell membranes
    • lecithinase: destroys lecithin in cell membranes
    • hemolysins: any enzyme that lyses RBCs
  34. how do pathogenic bacteria affect tissues?
    • bacteria causes tissue destruction by releasing byproducts during growth and metabolism (acids, gas, enzymes, toxins)
    • ex) lipases, nucleases (DNAse), proteases, pore forming proteins
  35. what are examples of bacteria that damage tissues (3)
    • clostridium perfringes: opportunistic anaerobic pathogen that destroys tissue releasing enzymes (phospholipase C, collagenase, protease, hyaluronidase) and metabolic byproducts (toxins, acid, gas)
    • staphylococci: modify host tissue with hyaluronidase, fibrinolysin, and lipase
    • streptococci: produce streptolysins S and O, DNAses, and streptokinases
  36. what are toxins
    • proteins produced by bacteria that interfere with normal host functions
    • includes (degradative enzymes that lyses cells, receptor binding proteins that initiate toxic reactions, promotes immune reaction)
  37. where are toxins encoded on?
    • plasmids 
    • pathogenicity islands
  38. how do toxins spread in the body
    by the circulatory system or body fluids
  39. what type of symptoms do toxins produce in the body
    food poisoning (S. aureus, B.cereus, C. botulinum)
  40. do toxins require bacterial growth to cause disease?
  41. what are exotoxins
    • proteins produced by microbes and released into their surroundings
    • produced by both G(-) and G(+)
    • ex) cytolytic enzymes
  42. what do cytolytic enzymes include
    • membrane disrupting enzymes (alpha toxin/phospholipase C)
    • hemolysins
    • pore formin toxins (streptolysin O)
  43. what are A-B toxins, what does it target, and symptoms
    • a type of extoxin that have two subunits (A and B)
    • targets ribosomes, transport machinery, intercellular signaling
    • symptoms: diarrhea, neuronal loss of function, death
  44. describe the components of A-B toxin and the function of each component
    • A subunit: enters into the cell and performs cytotoxic action
    • B subunit: binds to host cell surface receptor
  45. what are endotoxins
    • the lipid A portion of LPS on the outermembrane of G(-) bacteria
    • stimulates: fever, vasodilation, edema, inflammation
  46. what are superantigens
    • exotoxins that induce a cytokine storm (large activation of T cells without requiring an antigen) that cause life threatening fever, shock, rash, and autoimmune like response.
    • can lead to death
  47. how do endotoxins illicit an immune response
    binds to receptors on antigen presenting cells, stimulating release of acute phase cytokines
  48. what is sepsis
    when G(-) bacteria release high amounts of endotoxins in blood causing shock, hpotension, DIC (blood clots), or death
  49. what is the most powerful immune stimuli
    LPS: an endotoxin, that activates almost every immune mechanism including clotting pathway
  50. what disease symptoms does LPS induce (7)
    • shock
    • DIC, thrombosis
    • fever
    • hypoglycemia
    • incrs vascular permeability
    • incrs acute phase proteins
    • hypotensiondecrs iron
  51. how do capsules allow bacteria to evade immune system
    • capsules are virulence factors
    • shield bacteria from immune and phagocytic cells
    • mask bacteria as self mimicking human conenctive tissue
    • capsule is difficult to grasp for phagocytes
    • protect bacteria from destruction within a phagolysosome of a macrophage
    • contribute to biofilm formation
  52. what are the three ways bacteria can escape antibody respondes
    • antigenic variation: bacteria modifies their surface proteins to avoid begin detected by antibodies
    • antibody inactivation: by proteolytic degradation of antibodies/binding to antibodies to prevent their function
    • intracellular growth: when bacteria proliferate inside host cells to avoid being detected by immune cells
  53. how can bacteria evade phagocytic immune cells (5)
    • use enzymes to inhibit or lyse phagocytic cells
    • inhibit engulfgment of phagocytes
    • prevent lysosome phagosome fusion
    • exit the phagosome into the phagocytic cell cytoplasm
    • resist bactericidal lysosome compounds
Card Set
Bacterial Pathogenesis
how bacteria cause diseases