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