Staphylococcus

Question 1

Staph Identification

Answer 1

Gram + Cocci (Purple) + Catalase Positive +Form grapelike clusters

• S. Aureus is coagulase positive
• purulent

Question 2

Staph Strains

Answer 2

• S Aureas is Coagulase Positive

- S Epidermididis and others are Coag (-) “CoNS”

Question 3

Structural Virulence Factors

Answer 3

• Protein A: Binds Fc portion of IgG, prevents phagocytosis, complement activation, also camoflauges
• Polysaccharide Capsule: Impedes phagocytosis
• Biofilm: Protein and sugar rich secretion that protects “arrested” bacteria. Mostly in CoNS
• MSCRAMM’s- Adhesion molecules, assist in adherence to heart valves (endocarditis)
• Teichoic Acid-Adhesion to collagen and induces cytokine release.

Question 4

Secreted Virulence Factors

Answer 4

• Coagulase: Fibrin clot protects and walls off abcess
• Catalse: H2O2 -> H20 + O2. Prevents phagocyte killing
• Leukocidins: Kill leukocytes, PVL is common one that is present in staph induced necrotizing pneumonia
• Hyaluronidase: Allows for nutrient extraction and spreading

Question 5

Toxins

Answer 5

• A number of cytotoxins cause cellular damage and death
• Exfoliative toxin
• Toxic Shock Syndrome Toxin 1
• Enterotoxins

Question 6

Scalded Skin Syndrome (Ritters)

Answer 6

• Caused by exfoliative toxin that acts on stratum granulosum. There are no cells present in blisters, just toxin.
• Considerably more deadly in adult

Question 7

TSST1

Answer 7

• Toxic Shock Syndrome: is a superantigen that crosslinks T cells and activates a large number leading to:
  1. Fever
  2. Decreased BP
  3. Desquamating Rash
• For diagnosis rule out possible other agents and see involvment of multiple organ systems

Question 8

TSS Treatment

Answer 8

1. Manage BP with fluids and pressors
2. Remove source of infection, often in tampons or nasal packing, or surgically
3. Treat with antibiotics

Question 9

Emperical Treatment for TSS

Answer 9

1. Clyndamicin : Protein inhibitor
2. Vancomycin : Cell wall synthesis inhibitor (Gram +) (Be carfeul of Nephro and Ototoxicity)
3. Carbapeneam or piperacilin/tazobactam (broad spectrum inhibitors of cell wall sythesis)

Question 10

Specific Treatment

Answer 10

1. MSSA: Nafcilin
2. MSRA: Vancomycin or Linezolid
3. Group A Strep/Clostridium Sordelli: Pen G

Question 11

Food Poisining

Answer 11

Preformed heat stable enterotoxins. Treatment is conservative with few antibiotics and usually self limiting in 24hrs

Question 12

HA resistance

Answer 12

• Came first, resistance cassette is MecA which carries resistance to a number of antibiotics
• Structural aleration in PBP2a

Question 13

CA Resistance

Answer 13

• USA 300 is predominant strain and is now more common in both Community and Hospital than HA
• SCCmecIV is resistance cassete which carries fewer resistance genes
• Resistant strains take longer and are harder to kill, but not necessarily have worse outcome (death)

Question 14

Causes of TSS

Answer 14

1. S Aureus, CoNS
2. Streptococcus Pyogenes (group A Strep)
3. Clostridium sordelli

Question 15

Skin and Soft Tissue Infections (SSTI)

Answer 15

• Common, S Aureus is part of flora in 10-40% of people

- Furuncles/carbuncles, cellulitis, folliculitis

Question 16

Blood Stream Infection Diagnosis

Answer 16

1. Fever
2. Positive Blood Cultures
3. Decreased BP

Question 17

Impatigo

Answer 17

• Infection of the epidermis

- Can be caused by Staph, MSSA/MSRA or group A strep

Question 18

Blood Stream Infection Causes

Answer 18

• Can be caused by entry from other site

- Common to see CoNS entering from catheters and other prosthetic devices

Question 19

BSI Complications

Answer 19

• Endocarditis is largest complication, can cause damage to valves and also septic emboli that can cause stroke, infarction, or PE.
• MSCRAMM’s help staph adhere to heart valves

Question 20

BSI TTx

Answer 20

1.Start Antibiotics
2 Remove Source of infection
3. Transesophageal Echocardiogram

Question 21

Lung Infections

Answer 21

• Staph is less common than strep, but possible
• Necrotizing Pneumonia with Empyema when Staph is present.
• PVL is major virulence factor in Necrotizing Pneumonia

Question 22

CoNS Infections

Answer 22

• Very easy to get contaminated, many CoNS are commensals
• Easily enter and adhere to catheters or Prosthetic devices.
• If positive test result be suspicious of false positive, but more assurance if there is catheter or prosthesis

Question 23

Staphylococcus Summary

Answer 23

1. Gram + cocci that form cluster, Catalase (+) Coagulase (+/-)
2. S. Aureus is more virulent than other forms
3. Resistance is built to nafcilin and penecilin, use vancomycin instead
4. Toxins: Exfoliative, TSST-1, Enterotoxins
5. Endocarditis is most serious and common side effect of BSI with Staph
6. CoNS form biofilms and can easily infect catheters or prosthetic devices