Microbiology of Common Skin Pathogens-Bacterial

Question 1

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

Answer 1

• dryness

- low temperature and low pH

Question 2

What skin pathogen favors saltiness?

Answer 2

• Staph epidermidis

Question 3

What can cause skin lesions or rashes associated with microbes?

Answer 3

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

Question 4

What bacteria make up the normal skin flora?

Answer 4

• Staph epidermidis
• Propionibacterium acnes
• Corynebacterium minutissimum

Question 5

*** What is ERYTHRASMA?

Answer 5

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

Question 6

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

Answer 6

• Erythrasma fluoresces RED

Question 7

What are some predisposing factors for Erythrasma?

Answer 7

• excessive sweating
• obesity
• DM
• immunocompromised

Question 8

What are some TRANSIENT colonizers of the skin?

Answer 8

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

Question 9

What bacteria can colonize the skin from an EXOGENOUS SOURCE?

Answer 9

• Pseudomonas aeruginosa
• Pasteurella
• Clostridium perfringens

Question 10

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

Answer 10

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

Question 11

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

Answer 11

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).

Question 12

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

Answer 12

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

Question 13

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

Answer 13

• 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!

Question 14

What are the 3 types of ABSCESS forming infections?

Answer 14

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.

Question 15

What are the 2 types of NECROTIZING infections?

Answer 15

1. FASCIITIS

2. MYONECROSIS (gas gangrene)

Question 16

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

Answer 16

• Borrelia burgdorferi

* LYME disease

Question 17

What bacteria is associated with BULLOUS impetigo?

Answer 17

• Staph aureus (epidermolytic toxin)

Question 18

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

Answer 18

• Propionibacterium acnes

Question 19

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

Answer 19

Staph aureus

Question 20

What bacteria is associated with Hot-tub folliculitis?

Answer 20

• Pseudomonas aeruginosa

Question 21

*** What is Erythema nodosum?

Answer 21

• 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.

Question 22

Where does erythema nodosum appear most often?

Answer 22

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

Question 23

In what age group is erythema nodosum most seen?

Answer 23

• 18-34 year olds

* women mostly

Question 24

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

Answer 24

• Strep pyogenes

* usually occurs within 3 weeks of pharyngitis

Question 25

*** What is Erythema multiforme (EM)?

Answer 25

- 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.

Question 26

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

Answer 26

- Mycoplasma pneumoniae | * Note: HSV is the leading cause of recurrent erythema multiforme.

Question 27

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

Answer 27

- Staph aureus= coagulase + | - Step epidermidis= coagulase -

Question 28

Is Step pyogenes bacitracin sensitive or resistant?

Answer 28

- SENSITIVE | * also B-hemolytic

Question 29

Can Staph aureus or Step pyogenes cause a BULLOUS impetigo?

Answer 29

- Staph aureus | * both however can cause non-boullous impetigo.

Question 30

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

Answer 30

- Step pyogenes - also group G strep * transmission from nasal passages to area of skin.

Question 31

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

Answer 31

- Staph aureus (Exfoliated toxin A and B; ETA, ETB) | * toxin is a serine protease that cleaves desmosomes

Question 32

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

Answer 32

- 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.

Question 33

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

Answer 33

- 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.

Question 34

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

Answer 34

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

Question 35

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

Answer 35

- DM - Exfoliative dermatitis - prolonged steroid therapy - immunocompromised

Question 36

*** What is a SCARLATINIFORM rash?

Answer 36

- 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.

Question 37

*** What is Rocky Mountain Spotted fever?

Answer 37

- 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.

Question 38

*** What is Ecthyma gangrenosum?

Answer 38

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