Daniels-Staph

Question 1

Staphylococcus characteristics

Answer 1

Gram +
Cocci
Non-motile
Non-spore forming
Facultative anaerobes

Question 2

Staphylococcus identification

Answer 2

Positive catalase test

Coagulase test used to differentiate S. aureus (and 6 others) among 42 total species

Question 3

Staphylococcus diseases (S. aureus most common causative agent)

Answer 3

• Integumentary wounds
• Bacteremia
  
  • Organ abscesses
  • Endocarditis
  • Embolic pneumonia
  • septic arthritis
• Aspiration pneumonia
• UTI
• TSSS
• Scalded skin syndrome
• Food poisoning

Question 4

Staphylococcus reservoir and encounter

Answer 4

• On and around people
• Mucocutaneous junctions
• Skin and mucosal surfaces
• Can survive on surfaces, clothing, etc
• Usually behave commensally but may be opportunistic

Question 5

Staphylococcus entry

Answer 5

Damage to skin/ follicles
  -Wounds
  -Burns
  -Insect bites
Damage to mucosal surfaces

Question 6

Staphylococcus multiplication/spread

Answer 6

Varies based upon

• Bacterial inoculum (more worsens disease)
• Host immunocompetence
• Location of infection

Question 7

Staphylococcus adherence

Answer 7

MSCRAMMs-microbial surface components recognizing adhesive matrix molecules

• Fibronectin binding proteins
• Collagen binding protein
• Clumping factors
  
  • imp. for + coagulase test. in vitro
  • imp. for clot formation and endocarditis

Question 8

What is pus?

Answer 8

PMNs

Question 9

What do PMNs do?

Answer 9

• First to show up upon infection
• Phagocytosis
• ROS (these damage our tissues too)
• Cytokines for recruitment

Question 10

Virulence factors of S. aureus

Answer 10

• polysaccharide capsule-blocks phagocytosis
• protein A-blocks antibody function
• pore-forming toxins-pop PMNs leading to inflamm.
  
  • Panton-Valentine Leukocidin-very toxic to PMNs

Question 11

Disease manifestations of Staphylococcal toxins

Answer 11

• SSSS (staph. scalded skin syndrome)
• TSS (toxic shock syndrome)
• Staphylococcal food poisoning

Question 12

SSSS characteristics

Answer 12

• Exfoliative toxins A and B
  
  • Cause layers of epidermis to separate
  • Proteases that target desmosomes

Question 13

TSS characteristics

Answer 13

Involves TSST-1, which is a superantigen:

• Causes unregulated inflamm. response by activating CD4 cells
• Cross links TCR w/ MHC-II

This causes a cytokine storm via CD4 cells:

• IL1->fever
• TNFalpha + beta-hypotension and leaky vessels
• IFN gamma, IL2->rash

Question 14

Staphylococcal food poisoning

Answer 14

• Toxin preformed in contaminated, unrefrigerated food
• Intoxication not infection
• Many strains of S. aureus secrete enterotoxins
  
  • Enterotoxin A most common
• Superantigens cause intense peristalsis
• Cooking will kill bacteria but toxin is unaffected

Question 15

What are Penicillin Binding Proteins (PBPs)

Answer 15

Transpeptidases and transglycolases.

Makes crosslinks in peptidoglycan

Question 16

What inhibits PBPs

Answer 16

B-lactams:

• Penicillin and semi-synthetic variations
• Caphalosporins
• Carbapenems
• Monobactams

Question 17

PBPs of S. aureus

Answer 17

MSSA:
-PBP1, 2 and 3 required
MRSA:
-Additional PBP: PBP2a

Question 18

B-lactam resistance of S. aureus

Answer 18

• Penicillins- most strains resistant (blaZ penicilliniase enzyme)
• All other classes of B-lactams:
  
  • MSSA-susceptible
  • MRSA-resistant

Question 19

MRSA is resistant to B-lactams and what other drug classes?

Answer 19

• Macrolides/Lincosamides
• Sulfonamides
• Fluoroquinolones
• Tetracyclines

Question 20

What do we use to treat MRSA?

Answer 20

Vancomycin-glycopeptide class antimicrobial

• There are VRSA and VISA (vancomycin intermediate) strains
• Likely obtained VanA resistance gene from E. faecium via transposon

Question 21

MRSA epidemiology and infection sites

Answer 21

• Less than 1% of population but healthcare professionals make up 5-15% of those affected.
• 21% still carry MRSA 4 years post-diagnosis

Colonization sites:

• Nares
• Axilla
• Groin