Host-Microbe Interactions and Pathogenesis - Part 2

what is an infectious dose (ID50)

infectious dose is the number of cells or viruses needed to infect half of the people who are exposed to them

the lower the ID50,

the more virulent the pathogen is

what is a lethal dose (LD50)

the amount of a toxin required to kill half of hosts exposed to it if not treated

the lower the LD50,

the more potent the toxin is

what is an exotoxin?

exotoxins are made in the microbial cell and secreted into environment

what are endotoxins

endotoxins are typically part of the cell’s structures and released when the cell dies

• typically, by the antibiotic treatment or immune response

endotoxins: gram-negative bacteria have a molecule in their cell wall called lipopolysaccharide or …

LPS

LPS triggers a…

powerful body-wide inflammatory reaction

at low endotoxin levels, causes…

fever, chills, and hypotension (low blood pressure)

if endotoxin levels are high, this reaction can cause…

sepsis, which can damage organs and cause organ failure

as the immune system reacts, dying bacteria release…

endotoxin at levels that can cause sepsis if not caught in time

exotoxins come in 3 types:

• type 1 toxins

bind to receptors on the cells of their hosts and triggers an intercellular response

binding to receptors amplify signals inside of the cell that can…

alter cell physiology or lead to cell death

occasionally this may involve…

hyper-activation of B-cells or T-cells

an enterotoxin is a toxin that…

targets the intestines

E.coli enterotoxin is produced either…

during an active infection or during growth of the bacteria in food

when consumed the toxin binds to intestinal cells and causes them to…

leak salts and eater

E. coli bacteria that produce this enterotoxin cause…

food poisoning

food poisoning is specifically caused by…

exposure to enterotoxins

otherwise, the diarrhea, etc. are the result of an…

intestinal infection

staphylococcus aureus enterotoxin works differently, it is something called a…

T-cell superantigen

a superantigen is a toxin that…

hyper-activates adaptive immune cells

superantigens bind to and…

hyper-stabilizes the interaction between MHC and the T-cell receptor

this causes a…

massive cytotoxic T-cell response

this results in food poisoning by…

killing the cells of the lining of the digestive tract

type 2 toxins

break open holes in the membrane of host cells

this can cause the cell’s…

cytoplasm to leak into the tissue

• causes an inflammatory reaction

it can cause…

death of cells

a hemolysin is a toxin that…

destroys the membrane of red blood cells

hemolysins…

punch holes into the host cell’s membrane

• this causes water to rush into the cell by osmosis

• this irreversible flow of water bursts the cell like a popped balloon

hemolysis is detectable on cultures with sheep’s blood and is used to…

classify pathogenic bacteria

type 3 toxins

use a cell receptor to enter the cell

once inside the cytoplasm, they…

cause their toxic effect

these are also called…

A-B toxins because they are made of two parts

binding portion…

binds to receptor

active portion…

enters cell and has a toxic effect

pertussis is an infection of the…

lower respiratory tract and lungs

pertussis produces a variety of toxins, but the most serious is…

pertussis toxin

this toxin…

destroys the ciliated epithelial cells of the lung

leads to the build up of…

mucus and causes severe irritation of the lungs

the combination of irritation and mucus leads to the signature…

whooping cough symptom

botox primarily affects…

the nerve cells that cause muscle contraction, called alpha motor neurons

botox in the neuron…

blocks the release of the neurotransmitter acetylcholine

without acetylcholine signals,

the muscle cell cannot contract

leads to a paralytic condition called…

flaccid paralysis

tetanus intoxication also produces…

paralysis that by a different mechanisms

tetanus toxin…

blocks the release of the neurotransmitter glycine

this neurotransmitter normally causes muscle cells to…

relax

blocking the release of glycine causes a different kind of paralysis called…

spastic paralysis, where the muscle cannot relax

tetanus is often called lockjaw because spastic paralysis typically affects the...

muscles of the face and jaw first

1. the pathogen must…

adhere (stick) to the host’s tissues

• to do this, pathogens make a variety of adherence strucutres

2. the pathogen must…

invade tissues and acquire nutrients

• to do this, pathogens make a variety enzymes and binding proteins

3. the pathogen must…

evade the immune system long enough to replicate or reproduce

• pathogens have a variety of ways of confusing or suppressing the immune system

because they are so small, bacteria are extremely vulnerable to being…

removed by physical forces or fluid flow

bacteria have evolved several different kinds of structures for…

sticking to surfaces and cells

• called adhesion structures

fimbriae

adhesion structures made of protein

adhesins allow bacteria to…

attach to specific proteins on specific kinds of cells