Pathogens Flashcards
What have been a major cause of mortality and morbidity throughout history
Infectious disease
The virulence of the organisms differ with
Strains
Species
How pathogen is identified
The set of virulence genes that carries and expresses
Measure of the ability to cause damage tot he host depends on
Invasiness
Toxigenecity
What is invasiness
The ability of the microorganism to become established in the host, to overcome the host defenses and to spread in the tissues
What is toxigenicity
The capacity of the microorganism to produce substances known as toxins that damage specific tissues of the host
Explain the process of the microorganism pathogenisity in the body
Infection process include
1) exposure
2) adherence
3) invasion
4) multiplication
The disease phase
toxicity and invasiveness cause the tissues or systematic damage
What virulence factors are used to invade host tissues
- Adhesins
- Capsules
- Enzymes that destroy host tissues
- Invasins
- Type 3 secretion systems and type 4 secretion systems
What do adhesins do
Promote specific attachment to the host cell surfaces
One adhesin type is usually able to attach to
One or a few cell types, dedtermining the site of colonization
What are afimbrial adhesins
Glyco/lipo proteins (not filaments) mediate close attachment
What are fimbriae/pilli adhesins
Polymers, mediate loose attachment
What is the role of the capsule in bacteria
Prevents the pathogen from being destroyed by host immune cells (phagocytes)
Mediates attachment to host cells and to other bacteria
for what type of bacteria capsule is the essential virulence factor
Streptococcis pneumoniae
Haemophilus influenzae
Capsule is not only ___
Virulence factor (non pathogenic microorganisms may have a capsule too)
What makes the colonies of S.pneumoniae mucoid
The capsule
How the penetration of epidermis happens
Use a breach in the skin (wounds, surgery, catheter)
How does the penetration of the mucosa happen
Destruction of the mucosa: destruction of the single-cell layer or invasion of cells
What is invasion
Enter host tissues, multiply, and spread->destruction of host tissues
What is hyaloronidase
An enzyme that degrades hyaluronic acid, a sticky polysaccharide that holds host cells together, a component of ECM
What type of bacteria secrete hyaloronidase
Staphylococci
Streptococci
Clostridia
What is collagenase
Enzyme that degrades the protein collagen present in connective tissues(muscle, cartilage)
Who secretes collagenase
Clostridia
What is lecithinase enzyme
Degrades lecithin (phosphatidylcholine) in cell membrane -causes the lysis of red blood cells and destroys tissue cells
Clostridium perfingens are (aerobes/anaerobes)
Strictly anaerobe
What is gas gangrene
Done by Clostridium perfingens
Infection of a deep wound. Uses lecithinase to lyse host cells, collagenase and hyaluronidase to destroy ECM
Describe invasion with hyaluronidase
the activity of hyaluronidase causes host
cells to slough apart, allowing pathogens at an initial colonization
site to spread between host cells to attack subsurface tissues
What are hemolysins
Cause lysis of red blood cells and a variety of cell types.
What included in hemolysins
Some are enzymes (lecithinase, phospholipase), some are cytolysins(pore-forming)
What is alpha-toxin in Staphylococcal
Staphylococcal a-toxin is a pore-forming
cytotoxin that is produced by growing Staphylococcus aureus cells. Released as
monomers, seven identical protein subunits oligomerize in the cytoplasmic membrane
of target cells. The oligomer forms a pore, releasing the contents of the cell.
What is leucocidin
Causes lysis of leucocytes- white blood cells
Leucocidin is produced by
Staphylococci, streptococci and a few Gram-negatives
What are proteases
Degrade complement proteins and/or antibodies, produced by several bacteria
What is coagulase
Causes insoluble fibrin to be deposited on bacterial cells and cloaks the bacteria from the immune system
Coagulase produced by
Virulent staphylococci
After the bacteria formed a coat of insoluble fiber inside the cut, how do they get dispersed
They secrete streptokinase that dissolves clot and release pathogen in to the bloodstream
What are invasins
Surface proteins, or injected proteins, that allow microorganisms to enter cells (invade host cell)
What is the major virulence factor of intracellular pathogens
Invasins
What organisms use invasins
Mycobacterium
Salmonella
Listeria
Chlamydia
What is the advantage of invasins
Invasion of host cells, including phagocytes, protect the bacterial pathogens against the host immune system; good source of nutrients
To grow inside host cells, what should be modified
- Block phagosome maturation (block digestion)
- Increase size of the vacuole
- Acquire nutrients
- Block detection of intracellular infection and response (host defense)
Who uses T3SS and T4SS
Gram-negative pathogens
Explain how T3SS functions
Forms a channel through the bacterial cytoplasmic membrane, the periplasm, the outer membrane, and the host cell membrane so bacterial proteins can be injected into the host cell cytosol
Function of T3SS and T4SS
- Invasion of host cells
- Block phagosome maturation
- Take control of host cells
The other name for T3SS and T4SS
injectosomes
what is the difference between T4SS and T3SS
T4SS does not have needle-like structure on the tip that is injected in host membrane
Is the production of the toxins is necessary for the organism to be highly virulent?
No
If the organism does not produce toxins, so how the damage can be made
By the host’s own immune system or be a result of the large number of pathogens present
Bacterial pathogens are associated with two distinct categories of disease
- Infectious diseases (e.g.pneumonia, meningitis, syphilis): result from the pathogen’s growth
- Intoxication (e.g. food poisoning): result from the presence of a specific toxin
Two types of toxins
Exotoxins : secreted into the surrounding as the bacterial pathogen grows
Endotoxins: part of the bacterial pathogen
Characteristics of exotoxins
- Soluble
- Usually proteins, usually heat-labile (destroyed by heat)
- Highly immunogenic (antibody response inactivates exotoxins)
When exotoxins are secreted
When the organism is lysed
Exotoxins are extremely ___
Potent, amongst the most lethal substances known
How exotoxins are categorized
By the target -Neurotoxins -Enterotoxins(GI tract) -Nephrotoxins (kidney) -Hepatotoxins(liver) Etc.
What is the power of C. botulinum toxin
1 mg neurotoxin can kill 10^6 guinea pigs. 1 pound is enough to kill the entire human population
Exotoxins include
Extracellular enzymes (hyaluronidase, etc.) AB toxins
What are AB toxins
Modify host cells
How AB toxins work
Composed of 2 subunit ->enzymatic subunit(A) and binding /cell entry (B)
Subunit A modifies a target inside the host cell leading to damage to the host
Subunit B binds to specific cell receptors providing tissue/ cell type specificity
What is the example of A-subunit modification
ADP-ribosyltransferase
What does the toxin from Clostridium botulinum do
Neurotoxin
- Blocks acetylcholine (no normal muscle contraction) release in neuromuscular junction
- Flaccid paralysis
“Botox”
- Reduces wrinkles/frown
- Muscle spasms
- Hyperhydrosis(excessive sweating)
Clostridium botulinum toxin affect
Humans, cattle horses, ducks
Clostridium tetanii found in
Soil (spore form)
What is happening with Clostridium tetanii
The bacteria is able to infect puncture wounds and produce the toxin TeNT. The toxin diffuses away, enters the blood stream and acts on neurons
Tetanus toxin cause
Spastic paralysis: bowed spines, clenched arm and leg muscles, and locked jaws
How does Tetanus toxin
Muscle relaxation is normally
induced by glycine (G) release from inhibitory interneurons. Glycine acts on the motor
neurons to block excitation and release of acetylcholine (A) at the motor end plate.
(b) Tetanus toxin binds to the interneuron to prevent release of glycine from vesicles,
resulting in a lack of inhibitory signals to the motor neurons, constant release of
acetylcholine to the muscle fibers, irreversible contraction of the muscles, and spastic
paralysis. For the purpose of illustration, the inhibitory interneuron is shown near the
motor end plate, but it is actually in the spinal cord.
Infection by Vibrio cholerae is characterized by
Severe diarrhea, massive loss of fluid from the intestinal tract
What A and B toxins do in Vibrio cholerae
There is 5 B parts and 1 A part
B:bind to intestinal cells
A: activate adenylate cyclase, produce cAMP
How cholera enterotoxin works
Normally, Na+ from lumen goes to the blood and there is no net loss of Cl- movement
Colonization and toxin production by V.cholerae.
Activation of epithelial adenylate cyclase by cholera toxin (cAMP)
Na+ movement blocked, net Cl- movement to lumen
Massive water movement to the lumen; cholera symptoms.
What are endotoxins
Lipid A of LPS from Gram-negative bacterial pathogens
When endotoxins are released
During multiplication or lysis of bacterial cells
Endotoxins comparing to endotoxisn are (temperature)
Heat stable-> cannot be innactivated
Is there antobody response against endotoxins?
No, weakly immunogenic
What is the effect of endotoxins
Very effective activator of the immune system, produce general systemic effects: fever, shock, weakness, inflammation, diarrhea; septic shock
What is the important cause of syptoms in all Gram-negative bacteria
Endotoxins
What do exotoxins do with the immune system
They are highly antigenic: stimulates the host defense systems to produce antibodies that can neutralize the toxin
How vaccines for exotoxins are made
-A toxin should be inactivated by heat or formaldehyde
And then inactivated toxoids are injected to induce antibody response
WHat are toxoids
Toxins that do not have any toxicity , but still cause antibody response
The example of the vaccine that is done though toxoids
diphteria toxin (DTaP)
Is there a vaccine against endotoxin?
No, because they cannot be inactivated by heat or formaldehyde and converted to taxoid
What is pathogenicity islands
Section of the chromosome encoding virulence factors
Several genes that encode these virulence factors are found clustered together on the chromosome as pathogenicity islands
The type of fimbriae, enzymes for penetration encoded on the choromose
In what bacteria pathogenicity islands are found
Salmonella enterica and related gram-negative pathogens such as pathogenic strains
of Escherichia coli
