Bacterial pathogenesis Flashcards by Kathleen Carlos

What is immune selection and what is an example?

Bacteria know our immune system better than we do so they use it for their benefit
Relapsing fever is driving force for antigenic variation in Borrelia hermsii

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Pathogenic bacteria are often clonal. How do they differ from nonpathogenic bacteria?

They have additional virulence genes

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Is antibiotic resistance more commonly selected in a population or individual?

Population

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What are Koch’s postulates for?

Guidelines for establishing the cause of an infectious disease

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What are Koch’s postulates?

Microorganism found in all cases of disease and in right spot
Microorganism can be grown outside the host for several generations
Reinoculation of the cultivated microorganism causes the disease
Microorganism can be isolated from experimentally produced disease

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What are two examples of organisms that can’t be cultured?

Treponema pallidum (syphilis) - use rabbit testes
Tropheryma whipplei (Wipple's disease) - use PCR

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Name an organism that does not have an animal model?

Neisseria gonorrheae

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Transmissibility: is it better to have a clinically mild or strong disease?

Clinically mild because a well adapted bug doesn’t want to kill its host

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Why are there clinically symptomatic diseases?

Non-adapted host or pathogen (zoonotic bacteria)
Clinical symptoms that promote transmission
Disease manifestations that are due to host response to pathogen

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5 ways that bacteria can spread in the body?

Direct tissue spread
vascular
lymphatic
within macrophages
ascending/descending within body tracts

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Extracellular bacteria often cause disease via the effect of?

Toxins and enzymes

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Intracellular bacteria are able to do what?

Invade host cells and often cause chronic infections

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What are exotoxins?

Highly toxic proteins secreted by bacteria into the extracellular environment
Often have two subunits (A and B)

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What do the A and B subunits of exotoxins do?

A: active subunit with specific toxin activity
B: binds to specific host cell receptor; involved in entry of exotoxin into cell

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Corynebacterium diptheriae is an example of what? What is the mechanism?

AB subunit exotoxin

Inhibition of protein synthesis, cell death

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What is food poisoning commonly caused by?

staphylococcal enterotoxin or botulinum toxin

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What is usually required for toxin production to occur?

Active bacterial infection

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How does enterotoxin vibrio cholerae cause diarrhea?

It is an AB exotoxin that induces adenylate cyclase activity which increases cAMP which causes increased secretion of cell nutrients, causing diarrhea

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How does neurotoxin clostridium tetani work?

It is a AB subunit exotoxin that blocks inhibitory nt release which causes continuous stimulation by the excitatory nt … causing spastic paralysis

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How does the neurotoxin clostridium botulinum work?

AB exotoxin that blocks the release of ACH from vesicles which causes flaccid paralysis of muscles

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How does bacillus anthracis work?

3 proteins make up 2 toxins
“protective antigen” is the B subunit
The A subunits are: edema factor (an adenylate cyclase) and lethal factor (kills cells)

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superantigens vs exotoxins and fever?

Superantigens cause fever while exotoxins do not

Although some exotoxins are superantigens

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What are superantigens produced by?

bacteria and viruses

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How do superantigens work? Two examples?

Polyclonal stimulation of T cells to divide and produce cytokines
Staph Toxic Shock Syndrome Toxin-1
Strep exotoxins

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What are pyrogenic toxins?

Cause fever unlike other exotoxins

Exotoxins are partially denatured by treatment with what? What does it create?

Formalin, acid, or heat | Creates a toxoid (nontoxic but still antigenic)

What are toxoids used for? 2 examples

Immunization | Diphtheria and tetanus toxoids

Exotoxins are highly _________ and _______ labile

highly antigenic | heat labile

Endotoxin is also known as what? It is an integral part of what?

LPS - lipopolysaccharide | Gram - bacteria cell wall

Describe the LPS cascade that causes septic shock

Endotoxin in the bloodstream binds to receptors on macrophages which signals a cytokine release which activates inflammatory and coagulation cascades

Septic shock can also be caused by gram + bacteria, even though they don't have LPS... why?

Probably due to peptidoglycan even though it is less potent

What part of LPS is the toxic moiety?

Lipid A

Which is more toxic, LPS or exotoxin?

Exotoxin

Exotoxin: gram - or + ?

Both

Endotoxin: gram - or +?

gram -

Exotoxin vs endotoxin, how are they released?

Exotoxin is secreted | Endotoxin is released once cell is lysed

Which is more toxic, endotoxin or exotoxin?

Exotoxin

Which is more antigenic, endotoxin or exotoxin?

Exotoxin

Reaction to heat: endotoxin vs exotoxin

Endotoxin is heat table | Exotoxin is inactivated to form toxoid

Which causes fever, endotoxin or exotoxin?

Endotoxin causes fever and septic shock | However pyrogenic toxins cause fever, and some exotoxins are pyrogenic

Are all bacterial enzymes intrinsically toxic?

How to bacterial enzymes cause tissue damage? What are they destroying?

Connective tissue | Also degrades hyaluronic acid (hyaluronidase)

What is streptokinase?

Fibrinolysin - blood clots

What is coagulase?

Coagulates plasma

What is catalase?

Inhibits oxidative killing | Gram - don't have

What do cytolysins do?

Kill host cells

What is Streptolysin S?

Group A beta-hemolytic streptococci

What is the first step in entry to the host cell and secretion of bacterial proteins into the host cell?

Adherence to host cell

Antibodies against what can block adhesion of bacteria to host cells?

Antibodies against adhesin

What can cause pyelonephritis?

P pilus of E. coli

What is the type III secretion system? Which bacteria type have it?

Used for secreting bacterial virulence proteins into host cells Only in pathogenic gram -

For the secretion of bacterial proteins into host cells, what are their two different functions?

induce/prevent uptake by mammalian cell | induce/prevent death of mammalian cell

What is an example of a bacteria that induces uptake by a mammalian cell? One that prevents uptake?

Salmonella - invades mammalian cells | Yersinia - prevents phagocytosis by macrophages

What is an example of a bacteria that induces cell death? One that prevents it?

Yersinia induces apoptosis of macrophages | Chlamydia prevents apoptosis (intracellular bacteria)

What are three advantages of intracellular localization?

Nutrient rich environment Absence of competing microorganisms Protected from humoral immune system

Intracellular bacteria that survives inside a phagolysosome?

Coxiella

Intracellular bacteria that inhibits phagolysosomal fusion?

Chlamydia

Intracellular bacteria that escapes into cytosol?

Listeria

Diagram the intracellular life cycle of listeria

``` Entry by internalin Lysis of vacuole by listeriolysin O Escape into cytosol Actin based motility by ActA Spread to adjacent cell Lysis of vacuole... etc ```

What bacteria absorbs normal host component to surface of itself to avoid host immune system?

Staphylococcus aureus (protein A binds IgG)

What are 3 surface factors that inhibit phagocytosis?

Polysaccharide capsule M protein: group A streptococci Pili : neisseria gonorrheae

Why does the polysaccharide capsule aid in evasion of host immune system?

Prevents complement deposition and is poorly immunogenic Induces T cell independent immune response Response is poor in children <2

What are 3 bacteria that utilize the polysaccharide capsule to evade immune systems?

Bacteria that cause meningitis neisseria meningetidis streptococcus pneumoniae haemophilus influenzae

Are antibodies against polysaccharide capsular type general or specific? What do these antibodies protect against?

Have to be specific Protect against serious systemic infection Do not protect against mucosal colonization

Example of 2 bacteria that switch surface antigens?

neisseria gonorrheae: (lipooligosaccharide, pili, Opa proteins) borrelia hermsii - relapsing fever

What is an IgA protease, which 4 bacteria produce it?

Cleaves IgA, which is important for mucosal immunity | neisseria gonorrheae, neisseria meningitidis, haemophilus influenzae, streptococcus pneumoniae

Deposition of immune complexes cause tissue damage. What is an immune complex?

bacterial antigen, antibody, complement

What happens in post-streptococcal acute glomerulonephritis

Deposition of immune complexes in glomeruli of kidneys

What happens in post-streptococcal rheumatic fever?

Autoimmune process with antibodies against streptococcal antigen cross-reacting against host tissue

Where is extracellular iron bound in plasma and milk/other secretions?

Transferrin | Lactoferrin

What is an example of a bacteria that produces siderophores to capture iron?

E. coli

Bordetella pertussis has higher expression of virulence genes at what temperature?

Higher expression at 37 degrees than 20 degrees

Yersinia antiphagocytic factors have higher expression in the absence of what

Ca2+

Corynebacterium diptheriae toxin is more highly expressed in the presence of low what

Fe3+

What are three main mechanisms of antibiotic resistance?

Inhibition of antibiotic Target site alteration Decreased intrabacterial accumulation of antibiotic

Inhibition of antibiotic occurs by: | Example

enzymatic hydrolysis of antibiotic | Ex. enteric gram - bacteria that produce beta lactamases

Target site alteration occurs by: | 3 examples

Decreasing binding affinity for the antibiotic for the target penicillin resistant streptococcus pneumoniae expressing altered penicillin binding protein (PBP) methicillin resistant staphylococcus aureus expressing altered PBP vancomycin resistant enterococcus expressing altered cell wall oligopeptide

3 ways in which there could be decreased intrabacterial accumulation of the drug, and one example

Decreased membrane permeability Changes in porin channels Increased drug efflux often resulting in multidrug resistance Psuedomonas aeruginosa uses all 3 mechanisms

Can plasmids be passed by conjugation

Yep

One example of virulence genes encoded by a prophage?

vibrio cholerae

Streptococcus pyogenes containing erythrogenic toxin cause

scarlet fever

E. coli strains that produce shiga toxin cause what

hemorrhagic colitis and hemolytic uremic syndrome

What are examples of virulence factors? 5

``` Toxins Enzymes Type III secreted proteins Adhesins Siderophores ```

toxins were originally inactivated into toxoids by _________ and _______ but now can be genetically engineered

Heat, formaldehyde

What is antitoxin?

Antisera produced in response to the toxoid (from humans/animals) and can be given as treatment

Bacterial pathogenesis Flashcards

(85 cards)