Bacterial and Parasitic Infections of Skin

Question 1

what is the disease and rash caused by S. typhimurium?

Answer 1

• Enteric fever

- rose spot rash

Question 2

what is the disease and rash caused by N meningitides?

Answer 2

• meningitis

- petechial rash

Question 3

what is the disease and rash caused by t pallidum?

Answer 3

• syphillis

- secondary stage rashes

Question 4

what is the disease and rash caused by rickettsia?

Answer 4

• typhus

- hemorrhagic rash

Question 5

what is the disease and rash caused by measles virus?

Answer 5

• measles (duh dr. shillitoe)

- macular rash

Question 6

what is the disease and rash caused by s. aureus?

Answer 6

• TSS

- desquamation

Question 7

what is the disease and rash caused by b dermatidis?

Answer 7

• blastomycosis

- papular rash

Question 8

what is the disease and rash caused by s pyogenes?

Answer 8

• scarlet fever

- macules, glossitis (strawberry tongue)

Question 9

what is the disease and rash caused by viridans strep?

Answer 9

• bacterial endocarditis

- splinter hemorrhages

Question 10

what is the classification of S. aureus?

Answer 10

• gram +
• catalase +
• coagulase +

Question 11

what are the virulence factors for S. aureus

Answer 11

structural:
-protein A
-capsule
-coagulase
toxins:
-DNAse
-enterotoxin- GI problems
-exfoliatoxin-skin 
-leukocidin- kills WBCs
-TSS toxin- causes TSS

Question 12

list of conditions caused by staph

Answer 12

• impetigo-superficial
• abscess-follicles/sweat glands
• surgical site/wound infections-subQ or deeper

Question 13

list of conditions caused by strep pyrogenes

Answer 13

• impetigo-superficial
• erysipelas- subQ
• cellulitis-subQ or deeper
• necrotizing fasciitis-subQ or deeper

Question 14

reservoir and transmission of S. aureus

Answer 14

• Nasal carriers or infected patient pass to susceptible person via direct or indirect (fomite) contact
• nasal carriers can also “autoinnoculate” themselves in a susceptible site
• 30% of the population are nasal carriers

Question 15

skin layers (for this lecture)

Answer 15

• surface
• follicles/glands
• subQ
• deeper

Question 16

impetigo

Answer 16

• surface infection
• caused by S. aureus and S. pyogenes
• yellow crusted skin lesions, typically near nostrils
• can spread across face and appear on trunk and limbs
• more common in kids
• very contagious
• some cases show severe bullae- from exfoliatoxin
• diagnosis based on clinical appearance and history
• smears from pus may show gram + cocci in clumps or chain
• cultures show gram pos cocci that are either coag pos, B hemolytic, DNAse pos, salt resistant (s aureus) OR
• gram pos, coag neg, beta hemolytic, bacitracin sensitive (strep pyrogenes)

Question 17

impetigo treatment

Answer 17

• keep area clean and dry
• mild cases-mupirocin ointment, OTC creams won’t work
• severe cases- penicillinase resistant penicillins (nafcillin/oxacillin) or amoxicillin with penicillinase-inhibitor, or cephalosporins
• very extensive/drug resistant cases- get sensitivity test and prescribe appropriately- cephalosporin, clindamycin

Question 18

impetigo prevention

Answer 18

• cover lesions and discard dressings appropriately
• isolate infected children
• no sharing towels/ clothing
• laundry for infected clothing
• wash hands
• treat carriers topically- nose with mupirocin

Question 19

infected piercings

Answer 19

• coagulase negative staph-S. epidermidis- attaches to nylon and plastic
• entry site can be infected by biofilms, containing lg numbers of bacteria
• low grade pathogens form normal skin flora that stick to foreign material
• can be decorative or medical catheters
• diagnosis based on clinical features, lab culture shows gram pos, catalase pos, coag neg
• trtment- remove infected piercing/device
• prevent by changing all indwelling catheters or IVs on a regular shcedule
• use gold or surgical steel for piercings
• use triple antibiotic ointment on catheters in ICU and trt carriers

Question 20

scabies

Answer 20

• sarcoptes scabei- a mite, 1/2 mm long, 8 legs
• burrows into skin and lays eggs
• produces linear lesions which itch severely, due to cell mediated hypersensitivity
• transmission by personal contact or fomites
• diagnosed by clinical findings plus observation of mites in skin scrapings
• prevention through hygiene- change clothes regularly and DON’T SHARE TOWELS
• trt- topical steroids for itching, permethrin/ malathion to kill mites

Question 21

skin abscesses

Answer 21

• localized collection of pus
• may be deep or superficial, infected or sterile
• numerous forms:
• furunculitis, carbuncles, stye, acne
• usually due to S. aureus along with multiple non-pathogenic skin bacteria
• can also get breast abscesses

Question 22

furunculitis

Answer 22

• ingrown hair
• superficial sweat gland or follicle infections
• can be spread if itched
• stye is in the eye

Question 23

carbuncle

Answer 23

• larger multiple fused abscesses

- fused subcutaneously

Question 24

acne

Answer 24

• mixed infection involving increased susceptibility of the skin to infection
• small abscesses and superficial inflammation of the surface and sebaceous glands
• due to propionobacterium acnes- anaerobic
• treatment includes agents to reduce skin susceptibility and topical or systemic antibiotics

Question 25

diagnosis of skin abscesses

Answer 25

- clinical appearance and history - smears from pus she mixed bacterial pops - check for sensitivity - gram pos cocci - coag pos, beta hemolytic, DNAse pos, salt resistant (staph)

Question 26

trt for abscesses

Answer 26

- drain- have to remove all dead tissue and cover with dry dressing - mupirocin ointment for mild cases - systemic antibiotics if severe case (extensive, deep, fever) - nafcillin/oxacillin 1st, then cephalosporins - drug sensitivity testing may be needed- may be susceptible to clindamycin or methicillin, if not, use vanco or linezolid - some MRSA are resistant to all antibiotics - prevent by hygiene, remove carriers from ICU, nurseries, and ORs. trt carriers with ointment

Question 27

scalded skin syndrome

Answer 27

- widespread exfoliation due to localized infection with S aureus - toxin causes separation between epidermal cells - usually seen in newborns

Question 28

toxic shock syndrome

Answer 28

-systemic immune reaction to super antigen TSS toxin or strep TSS toxin

Question 29

cellulitis/erysipelas

Answer 29

- group A strep - infections beneath the surface of the skin that spread in a diffuse manner - erysipelas is superficial, cellulitis is deeper and associated with LAD, fever, and bacteremia - can lead to necrotizing fasciitis (which can also be caused by Clostridium perfringens and the plague)

Question 30

necrotizing fasciitis

Answer 30

- strep A- flesh eating bacteria- protease enzyme - starts as a minor skin infection which becomes rapidly extensive - spreads through subQ fascia with widespread necrosis and gangrene of extremities - no predisposing factors - fatal in 30% of cases - rare - not contagious

Question 31

diagnosis of cellulitis/necrotizing fascitis

Answer 31

- clinical features - cultures from blood/tissue often negative - strep etiology is assumed

Question 32

trt of cellulitis/erysipelas

Answer 32

-penicillin or cephalosporin

Question 33

trt for necrotizing fasciitis

Answer 33

- rapid surgical intervention, including amputation of affected digits or limbs - culture and sensitivity testing

Question 34

surgical site infections

Answer 34

- approximately 2.5% of surgical patients acquire infection of surgical site - with strep or staph - infections appear 5 days- 2 weeks after surgery - strep show signs similar to cellulitis - staph infections can lead to TSS - treatment by local excision and drainage, antibiotics won't help - elimination of carriers before surgery can reduce risk

Question 35

post strep nephritis

Answer 35

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