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MSS > Microbiology of Common Skin Pathogens-Bacterial > Flashcards

Microbiology of Common Skin Pathogens-Bacterial Flashcards

1
Q

What are some environmental influences that make the skin unfavorable for bacterial colonization?

A
  • dryness

- low temperature and low pH

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2
Q

What skin pathogen favors saltiness?

A
  • Staph epidermidis
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3
Q

What can cause skin lesions or rashes associated with microbes?

A
  • breakage of skin epithelium
  • tissue damage
  • exposure to toxins
  • damage to capillaries (rashes)
  • inflammatory response to infection (erythema nodosum or multiforme)
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4
Q

What bacteria make up the normal skin flora?

A
  • Staph epidermidis
  • Propionibacterium acnes
  • Corynebacterium minutissimum
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5
Q

*** What is ERYTHRASMA?

A
  • skin infection caused by CORYNEBACTERIUM MINUTISSIMUM
  • characterized by well demarcated, asymptomatic brown red, slightly scaly patches, usually found in axillae, groin and inner thighs.
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6
Q

How can you distinguish Erythrasma from Tinea cruris (dermatophyte)?

A
  • Erythrasma fluoresces RED
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7
Q

What are some predisposing factors for Erythrasma?

A
  • excessive sweating
  • obesity
  • DM
  • immunocompromised
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8
Q

What are some TRANSIENT colonizers of the skin?

A
  • Staph aureus
  • Strep pyogenes (Group A strep)
  • both can cause toxin mediated and non-toxin mediated infections.
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9
Q

What bacteria can colonize the skin from an EXOGENOUS SOURCE?

A
  • Pseudomonas aeruginosa
  • Pasteurella
  • Clostridium perfringens
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10
Q

*** What are the 3 types of SPREADING infections?

A
  1. IMPETIGO= confined to the epidermis.
  2. ERYSIPELAS= extends into the dermal lymphatics.
  3. CELLULITIS= involves dermis and subcutaneous fat.
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11
Q

*** What are the 3 subtypes of IMPETIGO (spreading infection)?

A
  1. NONBULLOUS impetigo= small vesicles, which rupture; purulent erosions with HONEY-COLORED CRUSTS (Staph aureus or Strep pyogenes).
  2. BULLOUS impetigo= large bullae (fluid-filled vesicle that CONTAINS ORGANISM; only Staph aureus).
  3. ECTHYMA= ulcerative form that extends deeper into the dermis (Staph aureus or Strep pyogenes).
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12
Q

** What is important to know about ERYSIPELAS (spreading infection)?

A
  • tender, red, and edematous lesions.
  • spread via LYMPHATICS in the dermis
  • more common in the ELDERLY (often LEGS or FACE).
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13
Q

** What is important to know about CELLULITIS (spreading infection)?

A
  • red, swelling, heat, and tenderness of the SUBcutaneous tissue (most commonly in the LOWER extremities).
  • rapidly spreading
  • inflammation of the LYMPH NODES.
  • due to Staph aureus, Step pyogenes, OR Pasteurella (from cat or dog scratch).
  • can develop into severe septicemia within 1-2 days!
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14
Q

What are the 3 types of ABSCESS forming infections?

A
  1. FOLLICULITIS= purulent infection of hair follicle.
  2. FURUNCLES (BOILS)= localized purulent inflammatory lesions of the skin and subcutaneous regions, formed from a folliculitis.
  3. CARBUNCLES= consists of several furuncles connected subcutaneously by sinus tracts.
    * caused by STAPH AUREUS.
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15
Q

What are the 2 types of NECROTIZING infections?

A
  1. FASCIITIS

2. MYONECROSIS (gas gangrene)

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16
Q

What bacterial pathogen is associated with ANNULAR PLAQUES (clearing in the center; bullseye)?

A
  • Borrelia burgdorferi

* LYME disease

17
Q

What bacteria is associated with BULLOUS impetigo?

A
  • Staph aureus (epidermolytic toxin)
18
Q

What bacteria is associated with acne vulgaris (purulent lesion)?

A
  • Propionibacterium acnes
19
Q

*** What bacteria is associated with folliculitis, furuncles, carbuncles (purulent lesions)?

A

Staph aureus

20
Q

What bacteria is associated with Hot-tub folliculitis?

A
  • Pseudomonas aeruginosa
21
Q

*** What is Erythema nodosum?

A
  • hypersensitivity reaction (inflammatory response in the subcutaneous fat).
  • causes painful deep nodules (may appear flat, but nodules are felt when palpated). Initially red, but become bluish and yellowish (like a bruise with time).
  • no ulcers and heal without scaring.
  • associated with fever, malaise, and arthralgia.
22
Q

Where does erythema nodosum appear most often?

A
  • usually on the LOWER LEGS, but can be on the arms or rarely on the face.
23
Q

In what age group is erythema nodosum most seen?

A
  • 18-34 year olds

* women mostly

24
Q

What is the most common INFECTIOUS cause of erythema nodosum?
*note: there are many non-infectious causes of erythema nodosum as well.

A
  • Strep pyogenes

* usually occurs within 3 weeks of pharyngitis

25
Q

*** What is Erythema multiforme (EM)?

A
  • inflammation with perivascular mononuclear infiltrate and edema in the upper dermis.
  • may be triggered by circulating immune complexes.
  • MILD= papules and plaques on extremities and face with TARGET LESIONS (especially on palms and soles; vesicle in center, surrounded by pale edema, which is surrounded by an outer zone of erythema); no systemic symptoms.
  • SEVERE (STEVEN-JOHNSON SYNDROME)= widespread lesions involving mucous membranes; often the result of drug reaction.
26
Q

With what bacterial pathogen is erythema multiforme associated?
*note: there are many other non-infectious causes of erythema multiforme as well.

A
  • Mycoplasma pneumoniae

* Note: HSV is the leading cause of recurrent erythema multiforme.

27
Q

What is one good way to differentiate Staph aureus from Strep epidermidis?

A
  • Staph aureus= coagulase +

- Step epidermidis= coagulase -

28
Q

Is Step pyogenes bacitracin sensitive or resistant?

A
  • SENSITIVE

* also B-hemolytic

29
Q

Can Staph aureus or Step pyogenes cause a BULLOUS impetigo?

A
  • Staph aureus

* both however can cause non-boullous impetigo.

30
Q

*** Is Staph aureus or Strep pyogenes associated with ERYSIPELAS?

A
  • Step pyogenes
  • also group G strep
  • transmission from nasal passages to area of skin.
31
Q

What pathogen is associated with scalded skin syndrome; SSS (toxin-mediated rash)?

A
  • Staph aureus (Exfoliated toxin A and B; ETA, ETB)

* toxin is a serine protease that cleaves desmosomes

32
Q

*** What pathogen is associated with SCARLET FEVER (toxin-mediated rash)?

A
  • Strep pygoenes (streptococaccal pyogenic exotoxin; Spe A and C)
  • preceded by pharyngitis, fever, headache, which causes a rash that progresses from the NECK to TRUNK, then EXTREMITIES.
33
Q

*** What is important to know about scaled skin syndrome (SSS)?

A
  • localized perioral erythema that spreads throughout the body over a few days (especially skin creases).
  • large blisters (bullae) contain clear fluid but not organisms or PMNs.
  • desquamation of the epithelium that resolves without scarring.
  • duration 7-10 days
    • NIKOLSKY’S SIGN= rubbing the skin results in blister formation with raw red base.
  • usually occurs in neonates or young children.
34
Q

What is important to know about BULLOUS impetigo (spreading infection)?

A
  • fluid-filled vesicles contain the organism (Staph aureus expressing ETA and ETB).
  • localized from of SSS
  • painless
35
Q

With what are carbuncles (caused by Staph aureus) often associated?

A
  • DM
  • Exfoliative dermatitis
  • prolonged steroid therapy
  • immunocompromised
36
Q

*** What is a SCARLATINIFORM rash?

A
  • sandpaper-like rash caused by Scarlet fever, resulting form Strep pyogenes.
  • blanches with pressure.
  • race is flushed with perioral pallor.
  • tongue initially has white coating, which then desquamates to become red with red papillae (STRAWBERRY TONGUE).
  • looks like a sunburn, but feels like sandpaper.
37
Q

*** What is Rocky Mountain Spotted fever?

A
  • rash accompanied high fever and other systemic associations (CNS, lungs, kidney, liver…) occurring from Rickettsia rickettsii (obligate intracellular pathogen transmitted via tick bite).
  • begins on WRISTS and ANKLES (palms and soles often involved).
  • initially blanchable, followed by nonblanchable petechial rash.
38
Q

*** What is Ecthyma gangrenosum?

A
  • NECTROTIZING VASCULITITS occurring due to PSEUDOMONAS aeruginosa septicemia.
  • red macule/papule becomes hemorrhagic with necrosis in the center.
  • ulcers develop a hemorrhagic rust (ESCHAR).

MSS (9 decks)

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