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MD1 SF3 - EXAM 2 > Le Staphylococcus aureus > Flashcards

Le Staphylococcus aureus Flashcards

1
Q

What is S. aureus?

A

Common human pathogen

  • 20-40% of humans
  • Infects everyone: patients in hospitals, and normal hosts within the community
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2
Q

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

A

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

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3
Q

What kind of bacteria is S. aureus?

A
  • 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

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4
Q

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

A

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
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5
Q

Gram negative vs. gram positive:

A
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6
Q

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

A
  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
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7
Q

Which toxins are present? (4 main kinds)

A

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
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8
Q

What is Panton–Valentine leukocidin (PVL)?

A

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

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9
Q

What are enterotoxins?

A

Gastrointestinal effects

In 30% of S. aureus strains

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

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10
Q

What is the main enterotoxin of S. aureus?

A

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
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11
Q

What are toxines exfoliatives?

A

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

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12
Q

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

A
  1. Generalized form (young pts) —> Staphylococcal Scalded Skin Syndrome
  2. Localized form (older kids and adults) —> Bullous impetigo
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13
Q

What is a superantigen?

A

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
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14
Q

What is toxic shock syndrome? (TSST-1)

A

TSST-1 is a superantigen

Leads to local production of toxins which disseminate throughout organism

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15
Q

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

A
  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)
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16
Q

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

A

Penicillin (all)

Methicillin (SARM)

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

< 10 strains —> resistant to vancomycin

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17
Q

Histoire naturelle de S. aureus?

A

Permanent colonization: 20% of people —> same clone

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

18
Q

Transmission/contamination de S. aureus?

A

Interpersonal, air, objects

19
Q

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

A

adhésion et infection

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

20
Q

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

A
  • Epidermis
    • Impetigo
  • Superficial dermis and hair follicles
    • Folliculitis
  • Deep dermis
    • Furoncles, carboncules, Hidradenitis suppurativa
  • Sub-cutaneous infection
    • Cellulitis, erysipelas
21
Q

What is impetigo?

A

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

The crust is yellow-brown, or honey-colored

22
Q

What is folliculitis?

A

Infection centered on hair follicles

23
Q

What are boils (furoncles)?

A

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

24
Q

What are carbuncles?

A

cluster of boils caused by bacterial infection

25
Q

What is erysipelas?

A

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

26
Q

What is cellulitis?

A

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.

27
Q

What is lymphangitis?

A

inflammation of the lymphatic system

28
Q

How are cutaneous infections treated?

A

Semi-synthetic penicillin —> cloxacillin

First generation cephalosporins

Clindamycin or vancomycin

29
Q

What is osteomyelitis? (3 ways)

A

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

30
Q

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

A

Pain above the site —> if no diabetic neuropathy

  • Sinus that’s draining ***
  • Exposed bone
  • Plaie à évolution très longue
31
Q

How is osteomyelitis dx and rx?

A

Microbiologically and radiologically

Longterm antibiotics, débridement chirurgical lors d’échec à l’antibiothérapie, d’infection chronique ou corps étranger

32
Q

What is septicemia?

A

Bloodstream infections… numbers on the rise:

  • more severe illnesses
  • IV drug usage
  • increase in corps étrangers

Starts fast… frissons, fièvre, douleurs diffuses (myalgia)

33
Q

Septicemia in physical examination:

A

Find “foyer infectieux”, hypo or hyperthermia, cutaneous eruption, respiratory distress

34
Q

How is septicemia dx?

A

Hemocultures to check for presence of bacteria in blood

Culture of infection site

35
Q

How is septicemia treated?

A

Remove corps étranger and treat all forms of S. aureus

IV antibiotics (length depends on presence of prosthetic material and if its still present)

36
Q

What is endocarditis?

A

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

37
Q

S. aureus and penumonia:

A

10% of community acquired pneumonia and 30% of hospital acquire

Often causes empyème (infection of pleural space)

38
Q

What are the clinical criteria for dx of toxic shock?

A

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

39
Q

How is toxic shock syndrome treated?

A

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

40
Q
A

MD1 SF3 - EXAM 2 (12 decks)

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