MICR130 Week 9 - Host-parasite Relationships

Symbiosis, mutualism, commensalism, parasitism

Symbiosis: a type of organism-organism relationship where at least one relies on the other

Types of symbiosis:

1. Mutualism: both benefit

2. Commensalism: one benefits, one unaffected

3. Parasitism: one benefits to the other’s harm

Nosocomial vs iatrogenic infections

HAIs (hospital-associated infections)

Nosocomial: acquired in hospital settings

Iatrogenic: acquires from medical procedures (a catheter, an infected wound)

Local infection

Invading microbe limited to a small area (a boil or abscess)

Systemic infection

Infection that spread via blood/lymph

Focal infection

An infection confined to one area that can spread to others via lymph/blood (eg. oral infections that spread to heart)

Sepsis

Inflammatory infection from spread of microbe, can lead to septicemia (blood poisoning)

Bacteremia, toxemia, viremia

Bacteria in blood

Toxins in blood

Viruses in blood

Primary infection

An acute, initial illness

Secondary infection

Aka superinfection

Opportunistic pathogen that arises after the primary infection weakens the body’s immune defenses (eg. Pneumocystis pneumonia after AIDs)

Subclinical infection

Asymptomatic

Pneumonia

A severe complication of the bronchi (air passage tubes from windpipe in lower respiratory system)

Meningitis

Inflammation of meninges (membrane surrounding brain and spinal cord)

Hepatitis

Inflammation of liver

Gastroenteritis

Inflammation of stomach + intestines

Exceptions to Koch’s postulates

• HIV, AIDS

  • Cannot be inoculated in animals

• Mycobacterium leprae (leprosy)

  • Cannot grow on artificial media in pure culture

• Treponema pallidum (syphilis)

  • Cannot grow on artificial media in pure culture

Ideal areas of body for microbial colonization

Mouth

• Moisture, warmth, presence of food

Stomach + intestines

• Moisture, nutrients

• Large intestine contains largest numbers of normal resident microbiota

Protein G and A

Cell wall protein in Streptococus pyogenes and Staphylococcus aureus that bind to antibodies to prevent normal function and evade phagocytosis

Bind to Fc region to flip the antibody backwards and appear “invisible”

Coagulase

Forms clots in organisms, enzyme present in Staph aureus

Streptokinase

Enzyme produced by Streptococci that dissolves blood clots, then purified for medical use

Hylaruonidase, collagenase

Dissolves hylaruonic acid + collagen

Siderophores

Scavenge free iron in environment then transport to cells, useful for treating iron deficiency

IgA protease

Digest certain types of antibodies - N. gonorrhae

Leukocidin

Cytotoxin produced by bacteria that kills leukocytes (white blood cells), esp Staph

Hemolysin

Bacterial proteins that break down red blood cells (esp in Strep)

Superantigen

Antigen that provokes an intense immune response, can lead to cytokine storm

Diptheria toxin

Phage with tox gene (lysogenized)

Inhibits protein synthesis in eukaryotes

Botulinum toxin

Neurotoxin, leads to flaccid paralysis

Cholera toxin

Choleragen

Stimulates adenyl cyclase in enterocytes (large intestine cells), which then dump water and electrolytes into small intestine

Erythrogenic toxin

Streptococcal superantigens, can cause scarlet fever and TSS

Complement system

In blood plasma, components produced by liver to stimulate release of histamine and attract phagocytes to promote phagocytosis