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88 Cards in this Set

  • Front
  • Back
What are 2 major differences between Corynebacterium diphtheriae and Staphylococci?
-C. diphtheriae is pathogenic but a good vaccine works for it
-No vaccine works for Staph species, but it's part of the normal flora anyway
What type of pathogen is staphylococcus, if it is at all?
What are 2 major problems associated with Staphylococcus infections?
-Multi drug resistance
-Genetic exchange induced drug resistance from Enterococci
What is the gram stain morphology of Staph?
-Gram pos cocci
-In short chains and clusters
What are the respiratory requirements of Staphs? Motility?
-Facultative anaerobes
What site is Staph a predominant normal flora?
Anterior nares
What is bad about Staph being in the normal flora?
Its hard to control infections
What staph is coagulase pos?
Staph aureus
What staphs are coag neg?
-Staph epi
-Staph saprophyticus
What does Coagulase do?
Converts fibrinogen to fibrin so it clots plasma.
What is the significance of there being >20 different staph species?
They are reservoirs for genetic exchange which serve to increase resistance.
Why does staph aureus like being a facultative anaerobe?
It gives it a competitive advantage over normal flora and during infections.
Why do we like it that Staph aureus can metabolize sugar under both aerobic and anaerobic conditions?
Because it allows us to identify it on mannitol salt when it produces the acid byproduct.
How do we differentiate Staph from Strep?
Via catalase (staph is pos)
What are the 3 major structures in the cell envelope of Staph?
-Teichoic acid
-Protein A
What does the tight and strong structure of PG in Staph's cell wall allow?
Survival in the environment for weeks - ie in dried pus and sputum; results in nosocomial spread of infection.
How can Staph be differentiated from Micrococcus?
By the presence of Teichoic acid in its cell wall.
What does peptidoglycan and teichoic acid on staphs stimulate?
Innate immunity via TLRs on macrophages.
Which staph has Protein A?
Only Staph aureus
How is Protein A situated on staph aureus?
Covalently bound to PG
What does IgG specific binding to Staph aureus normally do?
Results in opsonization
What does the presence of Protein A on the surface of Staph aureus do?
Binds the Fc receptor of IgG so that instead of causing opsonization, the Ab's are facing outward instead.
What is an assay that takes advantage of protein A's binding to IgG Fc regions?
An assay for detecting IgG antibody levels.
What is the way in which Staph aureus is pathogenic?
Production of many extracellular enzymes.
What are 5 extracellular enzymes produced by staph aureus?
1. Coagulase
2. Lipase
3. Hylauronidase
4. Staphylokinase
5. Nuclease
Are these extracellular enzymes exotoxins? Why?
NO - when purified and injected, they don't cause pathogenicity; only in the context of secretion from Staph aureus itself.
What does Coagulase do?
Clots plasma
What does Lipase do?
Assists in establishing colonization.
What does Hylauronidase do?
Hydrolyses hylauronic acid and facilitates spreading of the infection
What does Staphylokinase do?
Dissolutes clots (but there's little evidence this actually contributes to pathogenicity)
what does Nuclease do?
Cleaves DNA or RNA
Which of the extracellular enzymes is unique to Staph aureus?
What types of cells can be lysed by enzymes from Staph aureus?
-WBCs - via leukocidins
-RBCs - via hemolysins
What are 2 forms of coagulase associated with staph aureus?
What test detects Bound coagulase?
The slide agglutination test
What test detects secreted coagulase?
Tube coagulase test
Why would staph aureus want to coagulate fibrin?
Because it helps resist phagocytosis.
What are the 4 TOXINS produced by Staph aureus?
-Exfoliative toxins
What type of hemolysis does Staph aureus do?
Beta only
How do hemolysins produced by S. aureus cause pathogenicity?
By producing tissue damage after the establishment of a focus of infection
What type of toxin is Leukotoxin? What does it attack?
-A 2-protein toxin
-Attacks PMNs and Macrophages
What fraction of clinical isolates of S. aureus produce enterotoxin?
What are the clues of Staph aureus food poisoning?
-Projectile vomiting
-Symptoms within 2-6 hours after ingestion
Why do symptoms of Staph aureus food poisoning appear so quickly?
Because the toxin is preformed
How can Staph aureus enterotoxin survive baking and boiling?
It is heat stabile
What is the other Enterotoxin produced by Staph aureus?
Is Toxic shock a problem anymore?
No - specific tampon brands have been removed
What are enterotoxins?
What do Superantigens bind?
What gets stimulated as a result of the nonspecific binding of Super Ag?
20% of Tcells
What is the 3 bad results of stimulating 20% of one's Tcells?
-Massive cytokine production
-Systemic toxicity
-Suppression of the adaptive immune response
What are 2 forms of Staph aureus produced Exfoliative toxin, and what type of molecules are these?
What exactly does Exfoliative toxin lyse?
The intercellular attachments between epidermal cells
What syndrome is caused by Exfoliative toxin? In what patient population?
Scalded skin syndrome in infants
What is the treatment for Scalded skin syndrome?
Its self limiting
What is the most important route of transmission of Staphs?
What is the major human barrier to staph infection?
The skin
What is the primary site of infection caused by Staph aureus?
The skin
What are 4 skin infections caused by Staphs?
-Scalded skin syndrome
What does Staph cause in immunocompromised patients?
What are 2 other sites of staph infection? What diseases?
-Bone - osteomyelitis
-Joints - Arthritis
What tissue depth is involved in boils?
What is impetigo?
A mixed staph/strep infection that is highly infectious
What patients are considered immunocompromised and a target for Staph aureus pneumonia?
-Cystic fibrosis patients
-Flue patients
-Antibiotic treated patients
-Chemotherapy patients
-Immune suppressed patients
Why is PREVENTION of Staph aureus infections difficult?
Because it's part of our normal flora, thus we can't elicit immune memory via vaccination.
What is the main way to limit the spread of Staph aureus infection?
By using proper hygiene
How much Staph aureus is required to cause infection?
What are the 3 steps in treating Staph aureus infections?
1. Adequetely drain the wound
2. Remove foreign objects
3. Treat with antibiotics
What do you have to do in order to treat a Staph aureus infection with antibiotics?
1. Antibiotic sensitivity test
2. Identify multidrug resistant isolates
What is given if the Staph a is penicillin resistant (as is the case in 75% of cases)?
Give Methicillin
What is given if the Staph a is methicillin resistant (as is the case in 10% of cases)?
What causes methicillin resistance?
Mutations within the PBP's
What are the PBPs?
Carboxypeptidases and Transpeptidases
What is the drug of choice reserved for S. aureus infections?
How does Multi drug resistance develop?
Via the introduction of new genetic material via plasmid conjugation and transduction.
What Vancomycin resistant bug is a cousin of S. aureus and capable of transferring resistance to S. aureus?
What type of infection does Enterococcus cause?
Nosocomial in compromised hosts
How is Vancomycin resistance in enterococci mediated?
By plasmid transfer
What are the 2 gene products of plasmid mediated Vancomycin resistance?
-Van H
-Van A
What is Van H?
A reductase that converts pyruvate to lactate
What is Van A?
A ligase that ligates hydroxyl acids more efficiently than keto acids
What do VanH and VanA do together?
Condense lactate onto the pentapeptide of peptidoglycan on Staph aureus.
How does having a lactate instead of alanine on the peptidoglycan peptide chain make Enterococcus resist Vancomycin?
Vancomycin needs the alanine to be there in order to prevent crosslinking; if it's not there, crosslinking occurs in spite of the lactate and the bacteria continue to survive.
Does vancomycin resistance in Staph aureus follow the same mechanism as in Enterococcus?
But have we seen plasmid mediated transfer of that Enterococcal resistance to Staph aureus?
What are the coag neg staphs?
Staph epi
Staph saprophyticus
What does Staph epi bind and contaminate?
Binds Plastics and contaminates surgical sites
What infection does Staph saprophyticus cause? How
UTI - by tropically binding to urinary tract cells selectively