Portals of entry for microorganisms
Skin, mucous membranes, placenta, parenteral route (pretty much the same as portals of exit); ear, conjunctivae of eye, nose, mouth, broken skin, insect bite, urethra, vagina, penis, anus
Why should you not exfoliate?
You cause a little bit of damage and increase chances of bacteria accessing lower layers of skin and
Access through Skin
usually through broken skin, hair follicles, sweat glands; some can penetrate the skin
Protective mechanisms of skin
Sweat (enzymes, salt); barrier (tight); sloughs of dead skin cells; sebaceous glands (antibacterials, oils, lower pH); multiple layers (dead - few nutrients); dehydrated
Why are mucous membranes a portal of entry?
Living cells, thin layer, moist, warm; bacteria can exist there unless they can’t bind
Defensive mechanisms in mucous membranes
Mucous traps bacteria; Cilia move mucous; normal microflora; pH (of stomach); barrier (junctions); projectile vomiting; cells slough off; peristalsis
placenta
Usually microbes cannot cross placenta (cannot diffuse); only some (lysteria, some viruses) manage across and can cause abortion, birth defects
parenteral route
bypassing normal portals of entry; direct entry to tissues via nail, thorn, needles, cuts, bites
Opportunistic pathogens
ready and waiting to jump at the chance of infecting; ex. ones that infect immediately after taking antibiotics when normal microflora are gone
Manifestations of infectious disease
Signs, symptoms, syndrome
Symptoms
Subjective characteristics of disease
Signs
Objective manifestations - something shows up
Syndrome
Collection of symptoms and signs
Asymptomatic or subclinical
No signs or symptoms - spread more easily
Etiology
Study of the cause of a disease; must satisfy Koch’s postulates (but there are exceptions)
Exceptions to Koch’s postulates
Inability to culture organism; Disease caused by a combination of pathogens and/or physical, genetic, or environmental cofactors (e.g., liver cancer, meningitis, pneumonia); Some pathogens are ignored (don’t know they are there); Ethics and Koch’s third postulate (can’t infect a human)
Solution to exceptions of koch’s postulates
Use epidemiology; ex. we can’t inject HIV to prove it causes AIDS, but if HIV is found in every cause of the disease it makes a good case
Explain at a molecular level why we many not be able to fulfill Koch’s third postulate by using a different host animal
Could react differently because there are no receptors in the host so there is no binding
How could just binding to a cell cause disease?
Receptor mediated Endocytosis and get inside the cell; if it doesn’t enter, it may secrete toxins which enter cells
Adhesins
proteins on fimbrae that bind to complementary receptors on host cell
Gaining access after attachment
Enzymes: some break intercellular junctions (ex. collagenase); coagulase forms clot and bacteria are protected and break free later (quorum sensing)
Botulism and tetanus
Botulism inhibits muscles by completely relaxing them; tetanus inhibits muscles by completely contracting them
Toxemia
toxins enter the blood stream and cause a reaction elsewhere
Exoenzyme vs. toxin
Both are secreted and toxins are often enzymes, but toxins cause reactions elsewhere
