Unit 2 - Bacterial and Parasitic Infections of Skin

Question 1

what are structural virulence factors of S. aureus?

Answer 1

• Protein A
• capsule
• coagulase (main thing that separates pathogenic staph from non-pathogenic staph)

Question 2

what are toxin virulence factors of S. aureus?

Answer 2

• DNAse
• enterotoxin
• exfoliatin
• leukocidin
• toxic shock syndrome toxin

Question 3

bacteriology of S. aureus?

Answer 3

G+, catalase+, coagulase+

Question 4

what is the organism and rash associated with enteric fever?

Answer 4

S. typhimurium causes rose spots

Question 5

what is the organism and rash associated with meningitis?

Answer 5

N. meningitides causes petechial lesions

Question 6

what is the organism and rash associated with syphilis?

Answer 6

T. pallidum causes secondary stage rashes

Question 7

what is the organism and rash associated with typhus?

Answer 7

Rickettsia causes hemorrhagic rash

Question 8

what is the organism and rash associated with measles?

Answer 8

Measles virus causes macules

Question 9

what is the organism and rash associated with toxic shock syndrome?

Answer 9

S. aureus causes desquamation

Question 10

what is the organism and rash associated with blastomycosis?

Answer 10

B. dermatidis causes papules

Question 11

what is the organism and rash associated with scarlet fever?

Answer 11

S. pyogenes causes macules, glossitis

Question 12

what is the organism and rash associated with bacterial endocarditis?

Answer 12

Viridans streptococci causes splinter hemorrhages

Question 13

reservoir and transmission of S. aureus

Answer 13

nasal carriers –> susceptible site

nasal carriers or infected patient –> physical contact (direct or indirect fomites) –> susceptible person

Question 14

what are skin places that can be infected?

Answer 14

1. surface
2. follicles/glands
3. subcutaneous
4. deep

Question 15

what are surface infections and the organism responsible?

Answer 15

1. impetigo by S. aureus and S. pyogenes
2. leprosy by M. leprae
3. infected piercings/catheters from S. epidermidis
4. scabies from mites

Question 16

what are follicle/sweat gland infections and the organism responsible?

Answer 16

abscess from S. aureus

-specialized abscesses and small abscesses are called different things

Question 17

what are subcutaneous infections and the organism responsible?

Answer 17

1. erysipelas by S. pyogenes
2. cellulitis by S. pyogenes
3. necrotizing fasciitis by S. pyogenes and others
4. surgical site/wound infection by S. aureus and others

*last three also go deeper

Question 18

what is pyoderma?

Answer 18

generic term meaning any skin condition that produces pus

-includes impetigo, furunculitis, and carbuncles

Question 19

what is impetigo?

• appearance
• etiology

Answer 19

yellow-crusted skin lesions near nostrils (due to being ubiquitous in nose) that can spread across face and appear on trunk and limbs if touched

• more common in children, and very contagious
• severe cases show bullous impetigo

usually a mixture of strep and staph
–30% of population is a carrier, and may suffer periodic infections, or infect others by contact/fomites

Question 20

risk factors associated with impetigo?

Answer 20

sharing things (especially towels and soap), but less so skin injury and washing sweaty clothes

Question 21

how does one diagnose impetigo?

Answer 21

clinical appearance and history

• smears from pus may show G+ cocci:
• -in clumps, coagulase+, beta-hemolytic, DNAse+, salt-resistant are staph
• -in chains, coagulast-, beta-hemolytic, bacitracin-sensitive, reactive with grep group A antiserum are strep

Question 22

what is bullous impetigo?

Answer 22

severe impetigo associated with S. aureus due to exfoliatin

Question 23

treatment of impetigo?

-mild? severe? very extensive or drug-resistant

Answer 23

keep area clean and dry
mild: mupirocin ointment topically
-OTC antibiotic creams are less likely to be effective
severe: penicillinase-resistant penicillins (Nafcillin or oxacillin) or amoxicillin with penicillinase-inhibitor, or cephalosporins
very extensive: get sensitivity test and prescribe appropriately
-unlikely to need methicillin or vancomycin

Question 24

impetigo prevention

Answer 24

• cover lesions and discard dressing appropriately
• isolate infected kids
• don’t share towels, clothing, or laundry
• wash hands
• treat carriers topically (nose with muciporin)

Question 25

etiology of infected piercings and catheters? diagnosis?

Answer 25

Staphylococcus epidermidis attaches to nylons and plastic, establishing a biofilm to protect from immune system -start with attachment of low-grade pathogens from normal skin flora that stick to foreign material diagnose by clinical features -lab culture may show G+ cocci in clumps, catalase+, coagulase-, non-hemolytic

Question 26

treatment and prevention of infected piercings/catheters

Answer 26

remove infected piercing/device -elimination of biofilms by cleaning and antibiotics are not effective change all indwelling catheters on a regular schedule -use gold or surgical stainless steel for decorative pieces (not plastic)

Question 27

scabies etiology and transmission?

Answer 27

Sarcoptes scabei mite burrows into skin and lays eggs - produces linear lesions (due to burrowing just below surface) that itch severely, due to cell-mediated hypersensitivity - itching is worse at night - typically wrists or genitals - transmitted via personal contact or fomites (contagious)

Question 28

how do you diagnose, prevent, and treat scabies?

Answer 28

diagnose: clinical findings, plus observation of mites in skin scrapings prevention: hygiene (change clothes regularly, don't share towels) treatment: topical steroids for itching, and topical/systemic permethrin/malathion to kill mites

Question 29

what is the etiology of a skin abscess?

Answer 29

localized collection of pus (liquified tissue) that may be deep or superficial, infected or sterile -typically due to S. aureus, along with multiple non-pathogenic skin bacteria

Question 30

what are bacteria in acne? how is it treated?

Answer 30

a mixture of different bacteria, such as S. aureus and Propionobacterium acnes (anaerobic bacteria) treatment includes multiple ages to reduce skin susceptibility (retinoids, salicylic acid) as well as multiple empirical topical or systemic antibiotics

Question 31

what are different forms of skin abscesses?

Answer 31

1. furunculitis - superficial sweat gland or follicle infection - if you scratch it, it'll spread everywhere, so try not to 2. stye - eye and eyelash 3. carbuncle - multiple abscesses fused sub-cutaneously - can be deep, on face, knee, back of neck 4. acne - mixed infection involving increased susceptibility of skin to infection, with small abscesses and superficial inflammation of surface and sebaceous glands 5. breast abscess - gets in during breastfeeding to cause inflammation, tenderness, pain - still not "deep" to reach muscle, but far from point of entry

Question 32

how does one diagnose a skin abscess?

Answer 32

clinical appearance and history - obtain specimen for direct examination and culture - -smears from pus show mixed bacterial populations, including G+ cocci - -cultures show G+, coagulase+, beta-hemolytic, DNAse+, salt-resistant - evaluate antibiotic sensitivity

Question 33

how do treat skin abscesses?

Answer 33

1. remove dead tissue - drain abscess and cover with dry dressing - surgery if necessary 2. antibiotics - Mupirocin ointment for mild cases - systemic antibiotics if severe (extensive, deep, or fever): penicillinase-resistant beta-lactams or cephalosporins - drug sensitivity testing may be necessary; some MRSA are resistant to all

Question 34

how do prevent skin abscesses?

Answer 34

public health measures - remove carriers from ICUs, operating rooms, and newborn nurseries - carrier state can often be eliminated by topical Mupirocin ointment to nares

Question 35

what is scalded skin syndrome?

Answer 35

widespread exfoliation due to localized infection by S. aureus - exfoliatin toxin causes separation between epidermal cells - usually seen in newborns b/c no Ab

Question 36

what is toxic shock syndrome?

Answer 36

systemic immune reaction to super-Ag toxic shock syndrome toxin or streptococcal toxic shock syndrome toxin

Question 37

what is the etiology of cellulitis/erysipelas? difference between them?

Answer 37

infectious beneath surface of skin that spread in diffuse manner - erysipelas is superficial - cellulitis is deeper and associated with lymphadenopathy, fever, and bacteremia * terms are not well-defined

Question 38

what is necrotizing fasciitis etiology? how is this related to "flesh-eating bacteria"?

Answer 38

starts as a minor skin infection that rapidly becomes extensive, spreading through subcutaneous fascia with widespread necrosis and gangrene of extremities - no predisposing factors - fatal in 30% of cases - not contagious - rare - S. pyogenes is termed "flesh-eating bacteria" with potent protease enzyme

Question 39

how do you diagnose erysipelas, cellulitis, or necrotizing fasciitis? treatment?

Answer 39

diagnose via clinical featuers -cultures from tissue or blood are often negative, thus assume streptococcal etiology erysipelas and cellulitis treated with penicillin or cephalosporin NF treated with rapid surgical intervention, including amputation of affected digits or limbs, culture, and sensitivity testing -must make a diagnosis quickly

Question 40

what is the bacteria that causes erysipelas, cellulitis, and necrotizing fasciitis?

Answer 40

usually due to S. pyogenes

Question 41

etiology of surgical site infections? treatment?

Answer 41

approx 2.5% of surgical patients acquire infection of surgical site, frequently with streptococci or staphylococci - infections appear some 5 days to 2 weeks after surgery - streptococcal infections show signs similar to cellulitis, white staphylococcal infections cause toxic shock syndrome - treatment is by local excision and drainage; antibiotics have no effect - elimination of staph carrier state before surgery can reduce post-surgical infection

Question 42

what is post-streptococcal nephritis?

Answer 42

condition analogous to rheumatic fever, but tends to follow skin infections rather than pharyngitis -associated with particular M-protein types