Le Staphylococcus aureus

Question 1

What is S. aureus?

Answer 1

Common human pathogen

• 20-40% of humans
• Infects everyone: patients in hospitals, and normal hosts within the community

Question 2

What are the most common causes of S. aureus infections?

Answer 2

Post-op infections: have started doing pre-op decolonizations which has decreased infection rates by 45%

Skin infections, soft tissues, bones, and articulations

Can provoque other invasive infections: bacteremia, endocarditis, pneumonia

Question 3

What kind of bacteria is S. aureus?

Answer 3

• Spherical (cocci)
• Arranged in bunches (grappes/amas) —> staphylé = grappe de raisins
• Gram +
• Catalase + (hémolyse +)
• Also known as Staphylocoque doré

Can survive extreme conditions (extremophile): heat, dryness, salty environments

Question 4

What is the staphylococcus genus? (4 ones to know)

Answer 4

30 ish species:

• S. aureus (most common)
• S. lugdunensis (coag. -) —> same pathogenicity as S. aureus
• S. epidermis —> opportunistic bacteria (infection tied to prosthetic material)
• S. saprophyticus —> UTI in middle aged women

Question 5

Gram negative vs. gram positive:

Answer 5

Question 6

What is on the bacterial surface of S. aureus? (6 to know)

Answer 6

1. Polysaccharide capsule: antiphagocytaire
2. Adhésines: attached to peptidoglycan (surface proteins), allow for adhesion
3. Biofilm: matrice de protéine et polysaccharides —> limit diffusion of antibiotics and nutrients, bacteria in latency form
4. Acides teichoïques (AT) et acides lipoteichoïques (ALT): 50% of paroi, adhesion of enzymes to paroi/metabolism (AT) and inflammation (ALT)
5. Peptidoglycans: more than 10 layers in gram + and 2 in gram - (allows for rigidity), recognized by the immune system (cytokines —> inflammation)
6. Surface proteins (protein A): cache le peptidoglycans du système immunitaire —> capacité anti-phagocytaire

Question 7

Which toxins are present? (4 main kinds)

Answer 7

Hemolytic:

4 kinds: alpha, beta, gamma, delta

• alpha-hemolysine is the main one: polymerases on membrane of eukaryotes to create pores (important in pneumonia and endocarditis)
  
  • lysis of host cell —> releases cytokines
• Sphingomyelinase (toxine beta or beta-hemolysine): alters lipidic contents of membranes by enzymatic destruction
• Toxine delta: not really known
• Toxine gamma: leucocydine —> damages white blood cells

Question 8

What is Panton–Valentine leukocidin (PVL)?

Answer 8

cytotoxin—one of the β-pore-forming toxins.

• The presence of PVL is associated with increased virulence of certain strains (isolates) of Staphylococcus aureus
• protein that attacks polymorphonucléaires and macrophages
• analogous of gamma-hemolysin
• < 2% of S. aureus strains —> SARM-H, SASM
• In about 100% of SARM associated to community

Bad clinical evolution: infections cutanées et penumonies nécrosantes sévères

Question 9

What are enterotoxins?

Answer 9

Gastrointestinal effects

In 30% of S. aureus strains

6-8 million cases a year in the USA —> 10% hospitalized

Question 10

What is the main enterotoxin of S. aureus?

Answer 10

Entérotoxine A —> more than 15 described, resistant to heat so when bacteria is destroyed by heat toxins stay present in environment —> food poisoning

• Sx 2-6 hrs after ingestion —> N/V but no fever… usually resolves itself

Question 11

What are toxines exfoliatives?

Answer 11

A (phage) and B (plasmids)

Secretion of toxins in muqueuse or skin —> disseminated in organism

< 2% of S. aureus are carriers —> usually cause outbreaks in children under 1 year

Question 12

What are the two syndromes that toxine exfoliative are responsible for?

Answer 12

1. Generalized form (young pts) —> Staphylococcal Scalded Skin Syndrome
2. Localized form (older kids and adults) —> Bullous impetigo

Question 13

What is a superantigen?

Answer 13

Antigène qui active les lymphocytes T sans passer par la voie normale des cellules présentatrices d’antigènes

They induce:

• Non-specific proliferation of T lymphocytes
• Massive release of cytokines —> 20% of T lymphocytes activated
• Leads to exaggerated inflammatory response

Question 14

What is toxic shock syndrome? (TSST-1)

Answer 14

TSST-1 is a superantigen

Leads to local production of toxins which disseminate throughout organism

Question 15

What are the important enzymes to S. aureus? (5)

Answer 15

1. Coagulase:
   
   • Prothrombine —> causes coagulation of plasma and formation of clots
2. Staphylokinase:
   
   • Fibrinolysis, breaks thrombus and allows for dissemination of bacteria
3. Lipase:
   
   • colonization and invation
4. Hyaluronisase:
   
   • Hydrolyses acide hyaluronique in conjonctive tissue which allows for initial progression of cutaneous infections
5. B-lactamase:
   
   • Enzymes that hydrolytically destroy beta-lactams (antibiotic resistance)

Question 16

Which antibiotics can strains of S. aureus be resistant to?

Answer 16

Penicillin (all)

Methicillin (SARM)

SARM-AC (associated to the community) —> still effected by clindamycin… unlike SARM-HA (healthcare associted)

< 10 strains —> resistant to vancomycin

Question 17

Histoire naturelle de S. aureus?

Answer 17

Permanent colonization: 20% of people —> same clone

Intermittent colonization: 30% of people —> different clone (vagina, nasopharynx, skin)

Question 18

Transmission/contamination de S. aureus?

Answer 18

Interpersonal, air, objects

Question 19

Bris de la barrière muqueuse ou cutanée and S. aureus?

Answer 19

adhésion et infection

28-43 infections/ 100 000 people per year —> about 700k a year in the States

Question 20

Which layers of the skin are effected in different cutaneous lesions infected by S. aureus?

Answer 20

• Epidermis
  
  • Impetigo
• Superficial dermis and hair follicles
  
  • Folliculitis
• Deep dermis
  
  • Furoncles, carboncules, Hidradenitis suppurativa
• Sub-cutaneous infection
  
  • Cellulitis, erysipelas

Question 21

What is impetigo?

Answer 21

Macule that evolves towards vesicles due to epidermolytic toxins (80% S. aureus, 20% S. pygenes)

The crust is yellow-brown, or honey-colored

Question 22

What is folliculitis?

Answer 22

Infection centered on hair follicles

Question 23

What are boils (furoncles)?

Answer 23

deep folliculitis, infection of the hair follicle —> mostly in hairier areas

Question 24

What are carbuncles?

Answer 24

cluster of boils caused by bacterial infection

Question 25

What is erysipelas?

Answer 25

**common bacterial infection of the superficial layer of the skin** (upper dermis), extending to the superficial lymphatic vessels within the skin, characterized by a raised, well-defined, tender, bright red rash, typically on the face or legs, but which can occur anywhere on the skin

Question 26

What is cellulitis?

Answer 26

**common, potentially serious bacterial skin infection**. The affected skin appears swollen and red and is typically painful and warm to the touch. Cellulitis usually affects the skin on the lower legs, but it can occur in the face, arms and other areas.

Question 27

What is lymphangitis?

Answer 27

inflammation of the lymphatic system

Question 28

How are cutaneous infections treated?

Answer 28

Semi-synthetic penicillin —\> cloxacillin First generation cephalosporins Clindamycin or vancomycin

Question 29

What is osteomyelitis? (3 ways)

Answer 29

Hématogène —\> par plaque de croissance (+++ de vascularisation) * mostly in pediatrics Infection contiguë qui s'est étendue jusqu'à l'os * ex: foot ulcers in diabetic patients Penetrative trauma * ex: accident, fracture, post-op **S. aureus causes 50-70% of the cases**

Question 30

What are some clinical manifestations of osteomyelitis? (4 big ones)

Answer 30

Pain above the site —\> if no diabetic neuropathy * Sinus that's draining \*\*\* * Exposed bone * Plaie à évolution très longue

Question 31

How is osteomyelitis dx and rx?

Answer 31

Microbiologically and radiologically Longterm antibiotics, débridement chirurgical lors d'échec à l'antibiothérapie, d'infection chronique ou corps étranger

Question 32

What is septicemia?

Answer 32

Bloodstream infections... numbers on the rise: * more severe illnesses * IV drug usage * increase in corps étrangers **Starts fast... frissons, fièvre, douleurs diffuses (myalgia)**

Question 33

Septicemia in physical examination:

Answer 33

Find "foyer infectieux", hypo or hyperthermia, cutaneous eruption, respiratory distress

Question 34

How is septicemia dx?

Answer 34

Hemocultures to check for presence of bacteria in blood Culture of infection site

Question 35

How is septicemia treated?

Answer 35

Remove corps étranger and treat all forms of S. aureus IV antibiotics (length depends on presence of prosthetic material and if its still present)

Question 36

What is endocarditis?

Answer 36

**Infection of endocardia** —\> cardiac valves, septum (CIA and CIV), and sometimes the paroi cardiaque (VERY RARE)

Question 37

S. aureus and penumonia:

Answer 37

10% of community acquired pneumonia and 30% of hospital acquire Often causes empyème (infection of pleural space)

Question 38

What are the clinical criteria for dx of toxic shock?

Answer 38

Fever, hypotension, rash, desquamation of the fingers and toes, three or more systems are affected

Question 39

How is toxic shock syndrome treated?

Answer 39

Fluid replacement, penicillin resistant to B-lactames, preventing recurrences