Bacterial and Parasitic infections of the skin

Question 1

where is staph aureus carried in nonsymptomatic individuals? how is it transmitted?

Answer 1

in the nostrils

transmitted via direct contact or via fomites

Question 2

what are the two most common bacteria to cause infections of the skin?

Answer 2

staph aureus and strep pyogenes (group A strep)

Question 3

what part of the skin is infected by impetigo? what does it look like?

Answer 3

near the nostrils typically but can spread across the face, trunk and limbs
yellow crusted skin lesions

Question 4

what is bullous impetigo? what bacteria causes it and how?

Answer 4

an impetigo infection with severe bullae present

caused by s aureus releasing exfoliatin toxin

Question 5

what is the etiology of impetigo? what does a smear from the pus look like?

Answer 5

usually a mixture of strep and staph

smear shows gram positive cocci in clumps and/or chains

Question 6

what are the properties of cultures with impetigo? which organisms do they pertain to?

Answer 6

s. aureus- coagulase positive, beta hemolytic, DNAse positive and salt resistant
s pyogenes- coagulase negative, beta hemolytic, bacitracin sensitive and reactive with group A antiserum

Question 7

how is impetigo treated?

Answer 7

keep area clean and dry
mild- mupirocin ointment (OTC creams not effective)
severe- penicillinase resistant penicillins, amoxicillin with penicillinase inhibitor or cephalosporins
get sensitivity testing- unlikely to need methicillin or vancomycin

Question 8

how is impetigo prevented?

Answer 8

cover lesions and discard dressings. isolate infected children. don’t share towels or clothing and treat carriers with mupirocin

Question 9

how are piercings infected?

Answer 9

they are infected by biofilms with large numbers of bacteria that start by attachment of low grade pathogens from normal flora

Question 10

what is the most important organism in infection of piercings and catheters?

Answer 10

staph epidermidis- attaches to nylon and plastic

Question 11

what culture would probably be grown from an infected piercing?

Answer 11

gram positive cocci growing in clumps that are catalase positive, coagulase negative and non hemolytic

Question 12

what is the treatment for infected piercings and catheters?

Answer 12

remove the infected piercing or device (just cleaning and antibiotics will not get to all of the bacteria in the biofilms)

Question 13

how are infections of piercings and catheters prevented?

Answer 13

use gold or surgical stainless steel for piercings

change all indwelling catheters on a regular schedule

Question 14

what organism causes scabies? what does the rash look like and what causes it?

Answer 14

sarcoptes scabei- a mite
rash is a linear lesion that itches severely caused by mites that burrow into the skin and lay eggs. host has a cell mediated hypersensitivity reaction

Question 15

where does scabies infect, typically? how is it transmitted?

Answer 15

affects the wrists or genitals primarily. transmitted by personal contact or fomites

Question 16

how is scabies diagnosed? how is it prevented and treated?

Answer 16

diagnosed by observation of mites in skin scrapings
prevent by changing clothes regularly and not sharing towels
treat with topical steroids for itching and permethrin to kill mites

Question 17

what is an abscess? what are its forms?

Answer 17

a localized collection of pus (liquefied tissue)

ferunculitis (superficial infections), carbuncles (multiple fused subcutaneous abscesses), styes, and acne

Question 18

what is the most common cause of skin abscess? in acne, what is another major culprit?

Answer 18

staph aureus

acne also has propionobacterium acnes present

Question 19

what culture testing diagnoses s aureus infection?

Answer 19

gram positive, clustered cocci that are coagulase positive, beta hemolytic, DNAse positive and salt resistant

Question 20

how are skin abscesses treated?

Answer 20

abscess should be drained. mupirocin ointment for mild cases and systemic antibiotics if severe or with fever (nafcillin or oxacillin)

Question 21

what may be necessary before skin abscess treatment?

Answer 21

drug sensitivity testing may be necessary. last resort antibiotics are vancomycin or linezolid

Question 22

how is acne treated?

Answer 22

agents to reduce the skin susceptibility as well as topical or systemic antibiotics

Question 23

what public health measures are used to prevent skin abscess transmission?

Answer 23

remove carriers from ICUs, operating rooms and nurseries. carrier state eliminated by topical mupirocin ointment

Question 24

what is scalded skin syndrome?

Answer 24

widespread exfoliation due to a localized infection by s aureus and its exfoliatin toxin. it causes separation between epidermal cells usually seen in newborns

Question 25

what is the skin manifestation of toxic shock syndrome? what causes it?

Answer 25

systemic immune reaction to the super antigen TSS toxin. with sterile exfoliation lesions

Question 26

what organism typically causes cellulitis and necrotizing fasciitis?

Answer 26

group a streptococci (strep pyogenes)

Question 27

what is the etiology of cellulitis?

Answer 27

infections of the deep skin that spread in a diffuse manner. may be associated with lymphadenopathy, fever and bacteremia

Question 28

what is necrotizing fasciitis?

Answer 28

a minor skin infection that becomes rapidly extensive, spreading through subcutaneous fascia with necrosis and gangrene (noncontageous)

Question 29

what causes a skin infection to become necrotizing?

Answer 29

it produces a potent protease enzyme.

Question 30

what do the cultures from a cellulitis or necrotizing fasciitis demonstrate?

Answer 30

usually negative. diagnose with clinical features

Question 31

how is cellulitis treated? necrotizing fasciitis?

Answer 31

penicillin or cephalosporin

rapid surgical intervention including amputation. culture and sensitivity test for antibiotics

Question 32

what is erysipelas?

Answer 32

a superficial cellulitis that is not well defined.