Unit 2 - Bacterial and Parasitic Infections of Skin Flashcards
what are structural virulence factors of S. aureus?
- Protein A
- capsule
- coagulase (main thing that separates pathogenic staph from non-pathogenic staph)
what are toxin virulence factors of S. aureus?
- DNAse
- enterotoxin
- exfoliatin
- leukocidin
- toxic shock syndrome toxin
bacteriology of S. aureus?
G+, catalase+, coagulase+
what is the organism and rash associated with enteric fever?
S. typhimurium causes rose spots
what is the organism and rash associated with meningitis?
N. meningitides causes petechial lesions
what is the organism and rash associated with syphilis?
T. pallidum causes secondary stage rashes
what is the organism and rash associated with typhus?
Rickettsia causes hemorrhagic rash
what is the organism and rash associated with measles?
Measles virus causes macules
what is the organism and rash associated with toxic shock syndrome?
S. aureus causes desquamation
what is the organism and rash associated with blastomycosis?
B. dermatidis causes papules
what is the organism and rash associated with scarlet fever?
S. pyogenes causes macules, glossitis
what is the organism and rash associated with bacterial endocarditis?
Viridans streptococci causes splinter hemorrhages
reservoir and transmission of S. aureus
nasal carriers –> susceptible site
nasal carriers or infected patient –> physical contact (direct or indirect fomites) –> susceptible person
what are skin places that can be infected?
- surface
- follicles/glands
- subcutaneous
- deep
what are surface infections and the organism responsible?
- impetigo by S. aureus and S. pyogenes
- leprosy by M. leprae
- infected piercings/catheters from S. epidermidis
- scabies from mites
what are follicle/sweat gland infections and the organism responsible?
abscess from S. aureus
-specialized abscesses and small abscesses are called different things
what are subcutaneous infections and the organism responsible?
- erysipelas by S. pyogenes
- cellulitis by S. pyogenes
- necrotizing fasciitis by S. pyogenes and others
- surgical site/wound infection by S. aureus and others
*last three also go deeper
what is pyoderma?
generic term meaning any skin condition that produces pus
-includes impetigo, furunculitis, and carbuncles
what is impetigo?
- appearance
- etiology
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
risk factors associated with impetigo?
sharing things (especially towels and soap), but less so skin injury and washing sweaty clothes
how does one diagnose impetigo?
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
what is bullous impetigo?
severe impetigo associated with S. aureus due to exfoliatin
treatment of impetigo?
-mild? severe? very extensive or drug-resistant
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
impetigo prevention
- cover lesions and discard dressing appropriately
- isolate infected kids
- don’t share towels, clothing, or laundry
- wash hands
- treat carriers topically (nose with muciporin)
etiology of infected piercings and catheters? diagnosis?
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
treatment and prevention of infected piercings/catheters
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)
scabies etiology and transmission?
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)
how do you diagnose, prevent, and treat scabies?
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
what is the etiology of a skin abscess?
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
what are bacteria in acne? how is it treated?
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
what are different forms of skin abscesses?
- furunculitis - superficial sweat gland or follicle infection
- if you scratch it, it’ll spread everywhere, so try not to - stye - eye and eyelash
- carbuncle - multiple abscesses fused sub-cutaneously
- can be deep, on face, knee, back of neck - acne - mixed infection involving increased susceptibility of skin to infection, with small abscesses and superficial inflammation of surface and sebaceous glands
- breast abscess - gets in during breastfeeding to cause inflammation, tenderness, pain
- still not “deep” to reach muscle, but far from point of entry
how does one diagnose a skin abscess?
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
how do treat skin abscesses?
- remove dead tissue
- drain abscess and cover with dry dressing
- surgery if necessary - 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
how do prevent skin abscesses?
public health measures
- remove carriers from ICUs, operating rooms, and newborn nurseries
- carrier state can often be eliminated by topical Mupirocin ointment to nares
what is scalded skin syndrome?
widespread exfoliation due to localized infection by S. aureus
- exfoliatin toxin causes separation between epidermal cells
- usually seen in newborns b/c no Ab
what is toxic shock syndrome?
systemic immune reaction to super-Ag toxic shock syndrome toxin or streptococcal toxic shock syndrome toxin
what is the etiology of cellulitis/erysipelas? difference between them?
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
what is necrotizing fasciitis etiology? how is this related to “flesh-eating bacteria”?
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
how do you diagnose erysipelas, cellulitis, or necrotizing fasciitis? treatment?
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
what is the bacteria that causes erysipelas, cellulitis, and necrotizing fasciitis?
usually due to S. pyogenes
etiology of surgical site infections? treatment?
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
what is post-streptococcal nephritis?
condition analogous to rheumatic fever, but tends to follow skin infections rather than pharyngitis
-associated with particular M-protein types
