Host-Parasite Relationship

Question 1

Symbiosis/Mutualism

Answer 1

• Organism 1(initiates) benefits

- Organism 2 benefits

Question 2

Commensalism

Answer 2

• Organism 1 benefits

- Organisms 2 neither benefits nor is harmed

Question 3

Parasitism

Answer 3

• Organism 1 benefits

- Organism 2 is harmed

Question 4

Normal flora beneficial to healthy individuals

Answer 4

• colonization resistance: all the good spots are taken, fewer nutrients and physical locations for pathogens to set up residence
• nutrition:some gut bacteria produce nutrients

Question 5

Normal flora can cause disease

Answer 5

• commensals belong in particular sites on the body. If injury or poor hygiene carriers them elsewhere, they may cause symptoms at the new site
• immunosuppression can place host at risk of runaway infection by previously harmless organisms
• a commensal in the mother’s reproductive tract can be a pathogen in the neonate after vaginal delivery

Question 6

Skin commensals

Answer 6

• S. epidermidis and C. albicans are usually harmless, S. aureus will cause disease if not contained
• opportunistic pathogen: commensalism on the skin assumes that the skin is not broken

Question 7

Respiratory tract commensals

Answer 7

• Nose and throat-wide variety including strep, staph and Neisseria. Problems with overgrowhth of S. pyogenes, N meningitidis, S. aureus
• Mouth: Actinomyces and Kingella kingae. S. mutans in plaque causes cavities, can lead to heart valve trouble if dental hygiene is poor. Anaerobic bacteria in grooves in teeth can cause trouble when aspirated
• opportunistic pathogen- commensalism in the nose and throat assumes that the host is immunocompetent
• opportunistic pathogen- commensalism requires containment in the appropriate compartment

Question 8

Intestinal tract

Answer 8

• stomach is often clear of bacteria
• small intestine hosts strep, lactobacilli, yeasts
• colon is totally full of a huge variety of bacteria
• 20% by mass of stools
• most anaerobes
• most will cause serious problems if colon is punctured- the adjacent blood and organs are supposed to be sterile
• bacteroides, bifidobacterium, eubacterium, coliforms, enterococci, bactobacillil, clostridrium
• some mutualism in GI tract

Commensalism in the gut assumes that the gut is uninjured, can be thrown off by antibiotics

Question 9

Genitourinary tract

Answer 9

• vagina in women of menstruating age requires lactobacilli for maintenance of low pH
• candida overgrowth follows rising pH
• uropathogenic E. coli may set up stubborn colonizations of the area leading to recurring UTIs
• 15-20% of women carry group B strep, can cause sepsis and meningitis in newborns if delivered vaginally without antibiotics
• 5% colonized by S. aureus, predisposes to toxic shock syndrome

commensalism in the vagina- can be thrown off by changes in the vaginal pH, does not necessarily equate to commensalism in a neonate

Question 10

Innate Immunity and Colonization Resistance

Answer 10

-when bacteria first enter the body there are several options for their eventual fate:
successful colonization- nonPathogen-becomes pathogen; pathogen-causes dissease
failed colonization- pathogen cleared; nonpathogen cleared
-preventing pathogens from successfully colonizing the body is one function of innate immunity (including colonization resistance)
-once colonization with a pathogen has taken place, preventing it from killing the host is the role of adaptive immunity

Question 11

Innate immunity

Answer 11

• physical barrier (unbroken dry skin, mucus, cilia, nose hair, cough reflex)
• chemical barrier ( low vaginal pH, lysozyme, complement, fever, interferon)
• microbiologic barriers: colonization resistance
• immunochemical defenses- fever
• innate cellular defenses- complement, phagocytosis

Question 12

Koch’s Postulates

Answer 12

• gold standard proof-of-causality for an infectious agent causing a disease
• steps:
  i) observe a potential pathogen in sick animal
  ii) grow a pure culture of the pathogen
  iii) infect a new animal from the culture
  iv) observe the same disease in the new animal
  v) culture the same potential pathogen from the new animal
  vi) if fufilled, can say with certainity that the pathogen causes the disease

This is different from how patients are typically treated:

i) Patient reports symptoms
ii) tests uncover potential pathogen
iii) patient is treated for that pathogen
iv) if patient gets better, that way probably the problem
v) Do NOT mistake this process for proof