Dr. Daniels Staph

Question 1

Is the genus Staphylococcus Gram positive or gram negative?

Answer 1

Staph is gram positive

Question 2

Is the genus Staph motile and non-motile? Spore forming or non-spore forming?

Answer 2

The genus Staph is non-motile and non-spore forming

Question 3

Is the genus Staph aerobic or anaerobic? Be specific.

Answer 3

The genus Staph is predominantly facultative anaerobes

Question 4

How do you phenotype Staph?

Answer 4

1. Do a gram staining test -> Should stain purple for gram positive and be cocci
2. Do a catalase test –> Should test positive for catalase
3. Test growth in NaCl –> Should be able to grow in presence of 7.5% NaCl

Question 5

What does a coagulase test do when used with Staph bugs?

Answer 5

The coagulase test differentiates S. aureus and 6 others species which test positive from the 42 total species of Staph that are currently known

Question 6

What bacterium causes the highest burden of disease in people?

Answer 6

S. aureus causes the highest burden of disease in people.

Question 7

What bacterium is the most causative agent in the spectrum of disease?

Answer 7

S. aureus

Question 8

Name 7 common diseases caused by Staph aureus

Answer 8

1. Integumentary and wound diseases
2. Bacteremia
3. Aspiration pneumonia
4. UTI
5. Toxic Shock Syndrome
6. Scalded Skin Syndrome
7. Food poisoning

Question 9

Describe the ENCOUNTER step for Staph aureus

Answer 9

• Live on and around people
• Muco-cutaneous junctions
• Skin, mucosal surfaces
• Hearty environmental survival
• Usually behave commensally
• Opportunistic in right conditions

Question 10

Describe the ENTRY step for Staph aureus

Answer 10

• Damage to skin/follicles from wounds, burn, or insect bites
• Damage to mucosal surfaces

Question 11

Describe the SPREAD/MULTIPLICATION step of Staph aureus

Answer 11

• Varible depending on bacterial inoculum, host immunocompetence, and the location of infection
  Note: Bacteremia + immune compromise = trouble!!!

Question 12

What populations are at elevated risk for severe infections from Staph aureus?

Answer 12

• Young children/elderly
• Diabetics
• Individuals on immunosuppressive therapy
• HIV+
• Dialysis patients
• IV drug users

Question 13

What allows Staph to sick to the ECM

Answer 13

The MSCRAMM Fibronectin binding proteins FnbpA and FnbpB allow Staph to stick to the ECM of host cells

Question 14

What is the role of fibronectin

Answer 14

Fibronectin is a key player in the ECM function of adhesion - - acts like scotch tape holding cells together

Question 15

What is the role of Collagen binding protein (CNA) regarding Staph?

Answer 15

Collagen binding protein allows Staph to bind to collagen of cells

Question 16

What is the role of Clumping factors in regard in MSCRAMMs

Answer 16

Clumping factors bind fibrinogen and are important in clot formation. They are responsible for the positive coagulase test in vitro, and are key in pathogenesis of endocarditis.

Question 17

Describe the DAMAGE step of Staph aureus

Answer 17

Acute suppurative inflammation (aka accumulation of pus)

note: pus= neutrophils (PMNs/WBCs)

Question 18

Describe the immune cells role in abcesses

Answer 18

• PMNs arrive first at an abscess
• Phagocytosis of foreign invaders
• Release of toxic oxidative substances to try to kill bacteria (ROS)
• Release signaling molecules (cytokines) to call more WBCs to the area

Question 19

How do ROSs affect host tissue?

Answer 19

ROS payload damages host tissue resulting in sustained inflammation

Question 20

Describe the virulence factors of Staph aureus

Answer 20

• Polysaccaride capsule: blocks phagocytosis
• Protein A: blocks antibody function
• Pore-forming toxins: pop PMNs and other cells leading to more damage and inflammation (Panton-Valentine Leukocidin is very toxic to PMNs)

Question 21

What is SSSS?

Answer 21

SSSS is a disease of staphylococcal toxins, Staphylcoccal Scalded Skin Syndrom when Exfoliative toxins A and B caus ethe layers of the epidermis to separate.

Question 22

Describe exfoliative toxins

Answer 22

Exfoliative toxins are proteases with high-specificity for desmosomal proteins in the skin

Question 23

How does Staph aureus lead to Toxic Shock Syndrome?

Answer 23

A virulence factor of Staph aureus produces TSST-1 from oral abscesses which can lead to systemic response.

Question 24

Describe TSST-1

Answer 24

TSST-1 is a superantigen with causes an unregulated inflammatory response by activating high numbers of CD4+ T cells. Cross link T-cell receptor with MHC-II surface molecule of antigen presenting cells.

Question 25

Describe the cytokine response to TSST causing Toxic Shock Syndrome

Answer 25

TSST causes a cytokine storm by CD4+ cells releasing: - IL1 --> Fever - TNF alpha and beta --> Hypotension and capillary leakage - IFN gamma, IL2 --> Rash

Question 26

Describe Staphylococcal Food Poisoning

Answer 26

-Toxin is pre-formed in contaminated, unrefridgerated food. It is not an infection, but rather an INTOXICATION which causes illness. Many strains of S. aureus secrete enterotoxins which are HEAT STA BLE.

Question 27

What makes the crosslinks in peptidoglycan?

Answer 27

Transpepsidases and transglycosylases (Penecillin Binding Proteins) make the crosslinks in peptidoglycan, and these are the target sites of penecillin

Question 28

How are B-lactams effective against Penecillin Binding Proteins?

Answer 28

B-lactams antimicrobial agents are inhibitory substrates for PBPs because enzyme attach to the similar looking B-lactams instead of the Protein Binding Sites.

Question 29

Give 5 examples of common B-lactams

Answer 29

1. Penecillins 2. Semi-synthetic penecillins 3. Cephalosporins 4. Carbapenems 5. Monobactams

Question 30

Describe MRSA

Answer 30

Methicillin resistant Staph aureus which is resistant to PBO2a as well as PBP 1, 2, 3, 3', and 4. Will not allow b-lactams to act as inhibitory substrates and continue to hook the cell walls together for the S. aureus note: MSSA is similar

Question 31

Why is MRSA so concerning?

Answer 31

Because MRSA is resistant to penecillin, semi-synthetic and potentiated penecillins, cephalosporins, carbapenems and monobactams.

Question 32

How is resistance to drugs other than B-lactams significant with bugs like MRSA?

Answer 32

Drug resistant organisms like MRSA usually carry resistance genes to other drug classes as well. In the case of MRSA, it is B-lactams plus Cacrolides, sulfonamides, fluoroquinolones, and tetracyclines.

Question 33

What is the significance of Vancomycin in regard to MRSA?

Answer 33

-Vancomycin is a glycopeptide class antimicrobial drug commonly used to treat MRSA, but now there are resistant strands to vancomysin (VRSA and VISA) and in all isolates, the VanA resistance gene was found and presumably was horizontally transfered by Enterococcus faecium via conjugative transposon.

Question 34

What is the significance of MRSA epidemiology for healthcare workers in ohio in particular?

Answer 34

While typically less than 1% of the polulation carry MRSA, up to 5-15% of healthcare workers carry it. In some regions like ohio, greater than 50% of s. aureus infections are MRSA, and after a diagnosed MRSA infection, 21% of individuals still carry MRSA 4 years later

Question 35

What is the best defense against disease causing bugs?

Answer 35

Hand washing.