deck 7

Question 1

What bacterium is responsible for 90% of all bone infections?

Answer 1

Staph aureus

Question 2

In the case, the infected compound bone fracture was cleaned and re-set. After 6 weeks one bone was not set correctly. Why?

Answer 2

edema from the initial breaksinflammation from infection, leading to more edema

Question 3

How does osteomyelitis show on a radiograph? (radiopaque/radiolucent)

Answer 3

radiolucent where the normal bone opacity would be

Question 4

What are the characteristics of staph?Gram?shape?oxygen utilization?motile?forms spores?

Answer 4

Gram + coccus about 1um in diameterfacultative aerobes/anaerobesnonmotilenonspore-former

Question 5

What are the microbiology lab tests that distinguish staph aureus from other microbes?How are other staph different?

Answer 5

catalase + (distinguish from strep)coagulase + (other staph coagulase -)

Question 6

What are the three types of hemolysis?

Answer 6

beta - complete lysis of blood agaralpha - blood agar turning green due to change in oxidation state of iron in blood (from hydrogen peroxide and acids)gamma - no lysis on blood agar plate

Question 7

What microbe is responsible for: 500,000 cases of post-surgical infection annually100,000 cases of infectious endocarditis annually3K-35K cases of pneumonia (post-influenza)

Answer 7

staphylococcus aureus

Question 8

What is the number 1 cause of blood stream infections?What is number 2?

Answer 8

1) staph epidermidis2) staph aureus

Question 9

What diseases is staph aureus responsible for causing?

Answer 9

post-influenza pneumoniaendocarditisblood stream infectionsdeath in AIDs patientsUTIskin and soft tissue infections (boils)bone infections

Question 10

Staph aureus has a 10 year cycle. What is this significant for?

Answer 10

New strains emerge every 10 years (except TSST-1 staph aureus broke the cycle)

Question 11

Does staph aureus make toxins?What type of pathogen is it? Intra/extracellular?

Answer 11

It makes many cell surface and secreted toxinsIt is an extracellular pathogen with regard to PMNs and macrophages

Question 12

What is staph aureus resistant to?

Answer 12

drying and some antibiotics

Question 13

What are the cell surface virulence factors of staph aureus?(there are 5)

Answer 13

bound coagulase proteinfibronectin binding proteinscollagen binding proteinsvitronectin binding proteinsprotein A

Question 14

What is bound coagulase protein? What is its purpose?

Answer 14

It is a cell surface virulence factor that converts fibrinogen to fibrin to surround the bacterium with self and to wall itself off

Question 15

What is protein A? What is its purpose?

Answer 15

It is a cell surface virulence factor.It is a protein with 4 domains that bind the Fc portion of IgG and turn them backwards -> antiphagocytic

Question 16

What are the secreted virulence factors of staph aureus?(there are 16)

Answer 16

free coagulase protein4 hemolysins: alpha, beta, gamma, deltahyaluronidasestaphylokinaselipaseDNasesRNasesproteasesbeta-lactamasesPBP2a for methicillin resistanceTSST-1staphylococcal enterotoxinsstaphylococcal exfoliative toxins A & B

Question 17

What is free coagulase protein? What is its purpose?

Answer 17

It is a secreted virulence factor that activates the clotting cascade to presumably wall itself off

Question 18

What is alpha hemolysin toxin? What is its purpose?

Answer 18

It is a secreted virulence factor and is a 30K protein that homo-heptamerizes to form a pore in membranes. It is dermonecrotic for human skin and blocks nerve repolarization. (only hemolytic in rabbits)

Question 19

What is beta hemolysin toxin? What is its purpose?

Answer 19

It is a secreted virulence factor, is the hot:cold hemolysin, and is a sphingomyelinase

Question 20

What is gamma hemolysin toxin? What is its purpose?

Answer 20

It is a secreted virulence factor, is hemolytic, and is a 2 component hemolysin. There are multiple copies of both parts that come together as hetero-heptamer pore formers.

Question 21

What is delta hemolysin toxin? What is its purpose?

Answer 21

It is a secreted virulence factor and a small peptide that either acts as a surfactant to solubilize host cell membranes or is a small pore former

Question 22

Staph aureus can have redundant toxinsT/F

Answer 22

yes. this makes determining each toxin’s role in disease difficult

Question 23

What is hyaluronidase? What is its purpose?

Answer 23

It is a secreted virulence factor and spreading factor. It is an enzyme that cleaves hyaluronic acid in ground substance

Question 24

What is staphylokinase? What is its purpose?

Answer 24

It is a secreted virulence factor and spreading factor. It breaks clots that have formed in walling off the organisms

Question 25

What is lipase? What is its purpose?

Answer 25

It is a secreted virulence factor and an enzyme required for growth on the skin. Fatty acids in skin are toxic to bacteria and staphylococci have the ability to survive on the skin because of this

Question 26

What is TSST-1? What receptors does it interact with? What is the result?

Answer 26

Toxic shock syndrome toxin-1Secreted superantigen that cross links MHC-II alpha chain to the variable part of the beta chain of the TCR, resulting in massive cytokines released from macrophages/T cells

Question 27

What diseases is TSST-1 responsible for?

Answer 27

menstrual TSS1/2 of nonmenstrual staphylococcal TSS

Question 28

What are staphylococcal enterotoxins? What types are there? What receptors do they bind?

Answer 28

A-E and I and SE-like G, H, J-KThey are superantigens likeTSST-1 except different Vbeta-TCRs stimulated; some have two MHC-II sites

Question 29

What routes of administration of staphylococcal enterotoxins lead to what effects?

Answer 29

Oral - vomiting, diarrhea 2-8 hours after ingesting (no fever)IV or lungs - TSS

Question 30

What are staphylococcal exfoliative toxins? What types are there? What disease is caused in what age? Why are others resistant?

Answer 30

A & BSerine proteases that specifically cleave desmoglein 1 (only found in neonatal epidermis), causing separation of layers of the skin -> scalded skin syndrome in neonatesolder individuals are resistant due to the dominance of desmoglein 3 in adult skin

Question 31

T/FEvery staphyloccus aureus strain makes one of the cytolysins and one of the superantigens

Answer 31

True

Question 32

Where are most virulence factors found in the bacterial genome?

Answer 32

mobile genetic elements: pathogenicity islands, bacteriophages, plasmids

Question 33

T/FStaph aureus' core chromosome is relatively nonvirulent.

Answer 33

True

Question 34

What are the mechanisms of global regulation of secreted toxin production?

Answer 34

Histidine kinases in cell membrane sense oxygen and phosphorylate a response regulator (DNA binding protein). Octapeptides are produced, build up, and will activate Agr C. Then, it activates a response regulator to bind to DNA leading to RNA III production, which leads to delta toxin production and exotoxin transcription.

Question 35

What is the relevance of having an oxygen sensing system as a global regulator?

Answer 35

Staph won't make toxins until oxygen is present. This mechanism makes that happen. eg. menstrual TSS only happens with oxygen availability

Question 36

How are the MRSA strains classified?

Answer 36

HA-MRSA / CA-MRSAalso by pulse field gel electrophoresisUSA300USA400USA200USA100

Question 37

What DNA coding element is found on HA-MRSA? CA-MRSA?

Answer 37

HA-MRSA - SCCmec IICA-MRSA - SCCmec II or IV

Question 38

What is present in the SCCmec DNA coding element?

Answer 38

The gene that encodes PBP2a, which leads to resistance

Question 39

What are the highlights of the USA300 MRSA strain? Diseases it causes?

Answer 39

common on skin (lots of alpha toxin production & lipase)SCCmec IVcauses serious necrotizing pneumonia, usually in children, and soft tissue infections in all ages

Question 40

What are the highlights of the USA400 MRSA strain?Diseases it causes?

Answer 40

SEB+ or SEC+SCCmecIVcauses serious necrotizing pneumonia and TSS usually in children (nonmenstrual)

Question 41

What are the highlights of the USA200 MRSA strain? Diseases it causes?

Answer 41

TSST-1 +most common on mucosal surfacesSCCmec II or IVcauses serious necrotizing pneumonia and TSS in all ages; rarely causes skin infections

Question 42

What are the highlights of the USA100 MRSA strain?

Answer 42

HA-MRSAcommon

Question 43

What are the other Staph aureus virulence factors? These have less importance for virulence.Has vaccination against any of these been successful?

Answer 43

-capsules: small (more virulent) or large (less virulent)-slime (also called polysaccharide intercellular adhesion)-Iron-surface proteins (siderophores and related iron uptake systems)Vaccination has NOT been successful. The only vaccine candidates that have given complete protection are toxoids of exotoxins.