microbe-human interactions

normal flora

microbes which engage in mutualistic or commensal associations with humans

includes bacteria, fungi, and protozoa that live on the body without usually causing disease

found on areas exposed to the outside environment, not present in internal organs, and fluids

bacteria, which are normal flora in one location, can become pathogens somewhere else

steps of microbial exposure

finding a portal of entry

attaching firmly

surviving host defenses

causes of damage and disease

exiting host

portals of entry

skin

GI tract

respiratory tract

urogenital tract

placenta/ birth canal

STORCH

infectious dose

the minimal number of microbes required for infection

→ assuming a person is healthy, doesn’t factor in things like immunodeficiencies. compromisation

microbes with small ID are more virulent

lack of ID will not result in infection

mechanisms of adhesion

fimbria

capsules

surface proteins

viral spikes

hooks

surviving host defenses and causing disease

virulence factor: properties that improve a microbes invasiveness

some trait that enables a microbe to cause disease better

3 categories:

-exoenzyme

-toxins

-antiphagocytic factors

exoenzymes

an enzyme secreted out of the cell to perform a function

digest epithelial tissue and permit invasion of pathogens

mucinase

keratinase

collagenase

hyaluronidase

mucinase

digests the protective coating on mucous membranes

keratinase

digests the principal component of skin and hair

collagenase

digests principal fiber of connective tissue

hyaluronidase

digests hyaluronic acid

hyaluronic acid: the glue between cells

toxins

chemicals that have poisonous effects on other organisms

endotoxins

exotoxins

endotoxins

a toxin that is released only after the cell is damaged or lysed (dead)

found in gram-negative bacteria → can be more harmful/ impactful with the use of antibiotics as they kill/ breakdown cells → releasing endotoxins

exotoxins

a molecule secreted by a living microbial cell into infected tissue

antiphagocytic factors

help microbe kill or avoid phagocytes (white blood cells)

ex.

-slime layer

-substances that kill white blood cells (leukocidins)

pattern of infection

localized infection

systematic infection

mixed infection

primary infection

secondary infection

localized infection

microbes enter body and remain confined to a specific tissue

systematic infection

infection spreads to several sites and tissue fluids usually in the bloodstream

most common way to develop is through the bloodstream

systematic = everywhere

mixed infection

several microbes grow simultaneously at the infection site

primary infection

initial infection

secondary infection

another infection by a different microbe

portals of exit

respiratory, saliva

skin

fecal

urogenital

blood

*most are the same as portals of entry, one microbe may enter and exit at the same site

patterns of transmission

direct contact → portal of exit meets the portal of entry

-airborne

-insect bites

-std

indirect contact → something between the portal of exit and entry

-food, water, fomites

nosocomial infections

diseases that are acquired during hospital stays

most involve the urinary tract, respiratory tract, surgical incisions

most common are gram-negative enterics → usually due to poor handwashing

vector

a living thing that carries a pathogen from a reservoir (harbors disease) to a person

mechanical = not infected, just a carrier

biological = infected

epidemiology

study of frequency and distribution of disease and health-related factors in human population

world health organization

center for disease and control prevention

endemic

disease that exhibits a relatively steady frequency over a long period of time in a particular geographic locale

ex. Lyme disease in Northern MN

sporadic

when occasional cases are reported at irregular intervals

ex. food borne illness outbreak

epidemic

when the prevalence of a disease is increasing beyond what is expected

ex. measles outbreak

pandemic

epidemic across continents

ex. covid

most start as an epidemic

benefits of living with microbes

they take up space and nutrients that could otherwise be pathogens

antagonize pathogens by producing substances that inhibit or kill them

provides constant stimulation of the immune system. this is a vital role in the development of our immune systems

normal GI flora makes Vit K and some of the B vitamins, which are absorbed into the bloodstream