Kozel: Skin and Soft Tissue Infections II Flashcards
Gram positive bacillus
Aerobic and facultative anaerobe
Spore former
200 species
Bacillus spp.
What is unique about the capsule of Bacillus spp? What is its role?
it is a polypeptide (poly-D-glutamic acid) capsule instead of a polysaccharide capsule;
it is antiphagocytic and induces protective immunity
What type of toxin is associated with Bacillus spp?
A-B type toxin
What are the three antigens on the Bacillus toxin?
Protective antigen - induces protective immunity
Lethal factor - produces cell death
Edema factor - produces edema
Follows inoculation with spores
Painless papule progresses to ulcer to necrotic black eschar (malignant pustule)
cutaneous anthrax
Follows ingestion of spores
Local infection that may spread to systemic disease
GI anthrax
Follows inhalation of spores
Lungs → regional lymph nodes → systemic spread
Hypotension, pulmonary edema, massive bacteremia, acute fatal toxic shock
May have prolonged incubation period
Fatal if untreated
Inhalation anthrax
What type of specimen would you obtain for Bacillus infection?
blood or material from eschar
What would you see on the blood culture of Bacillus spp?
gram-positive rods in chains, capsule can be seen via negative stain
Bacillus infection is primarily a disease of (blank); humans are normally infected by exposure to (blank) or (blank) products
herbivores; animals; animal
Is there a human vaccine for anthrax?
yes, there is also a live vaccine for animals
What is the treatment for antrax poisoning?
ciprofloxacin
there is also a potential for monoclonal antibodies to protective antigen
**can use prophylaxis for exposed individuals or vaccinate with AVA
Gram-positive bacillus Anaerobic Spore-formers Ubiquitous in soil, water, sewage Normal flora of GI tract of man and animals Produce numerous toxins
Clostridium spp.
What is the major lethal toxin produced by C. perfringens in gas gangrene? What does this toxin do?
alpha toxin; lecithinase, lyses numerous host cells and causes massive hemolysis
This is another toxin released by C. perfringens when cells undergo sporulation
Altered membrane permeability – loss of fluids and ions
Superantigen
enterotoxin
What 3 diseases can be caused by Clostridium perfringens infection? What are the symptoms of each?
Cellulitis and gas gangrene: spores introduced by trauma or surgery, causes intense pain, muscle necrosis, shock and renal failure
Food poisoning: ingestion of contaminated meat leads to ab cramps and watery diarrhea
Necrotizing enteritis: ingestion of contaminated meat leads to necrosis of the small intestine
Where is Clostridium perfringens found?
ubiquitous in soil, water, and human GI tract
What is the treatment for C. perfringens?
for soft tissue infections: rapid treatment necessary, surgical debridement as needed and high dose penicillin + clindamycin
for food poisoning: antibiotics not effective, symptomatic treatment
Weakly gram-negative, motile, spirochete
Complex nutritional requirements; can be grown in culture
Borellia burgdorferi
What occurs during the early localized infection in Lyme disease? Early disseminated disease? Late in infection?
early localized infection: incubation period of 3-30 days, characteristic skin lesion (erythema migrans) at site of initial infection
early disseminated disease: days to weeks after onset of erythema migrans, multiple secondary annular skin lesions, fatigue, arthritis, myalgia, cardiac dysfunction
late infection: months after initial infection, more extensive arthritis, chronic skin involvement and neuro symptoms
What occurs with post-Lyme disease syndrome?
symptoms similar to chronic fatigue syndrome or fibromyalgia
What is acrodermatitis chronica atrophicans?
bluish-red skin lesions
occur in late, disseminated stage of lyme disease
When diagnosing Lyme disease, what do you look for?
erythema migrans (5cm)
or
at least one late manifestation (musculoskeletal, CNS, or cardiovascular) + lab confirmation
What is the lab test of choice for diagnosing Lyme disease?
antibody detection
IgM peak after 6-8 weeks
IgG peak after 4-6 months
What is the vector for Lyme disease? What is the reservoir?
hard ticks (nymph stage causes >90% of cases); white footed mouse or white-tailed deer
Where is Lyme disease seen in the US?
NE and mid-Atlantic states, upper midwest and Pacific west
What is the drug of choice for Lyme disease?
doxycycline for early disease
IV ceftriazone for recurrent arthritis or CNS/PNS disease
Gram-negative rods
Aerobic
Obligate intracellular parasites – grow only in cytoplasm of eukaryotic cells
Maintained in animal and arthropod reservoirs and transmitted by arthropod vectors
Humans are accidental hosts
Rickettsia
Rickettsia replicates in cytoplasm/nucleus of (blank) cells; causes (blank) due endothelial cell damage and leakage of blood vessels
endothelial; vasculitis
How does Rickettsia present clinically?
7 day incubation after bite
high fever, headache, malaise
macular rash w centripetal spread which becomes petechial
complications include pulmonary, CNS, renal or cardiac abnormalities
What are two methods of antibody detection for Rickettsia?
Weil-Felix test: detects antibodies that cross-react with a Proteus antigen
Indirect immunofluorescnece: detects ab against outer membrane protein and LPS**
What is the principal reservoir and vector for Rickettsia? Where is it found?
ticks; throughout the US
Treatment for Rickettsia?
doxycycline
**early treatment is critical
What do the following cause?
Orientia tsutsugamushi?
Rickettsia prowazekii?
Rickettsia typhi?
What symptoms are common to all?
scrub typhus *sudden onset
epidemic typhus *sudden onset
murine endemic typhus *gradual onset
**fever, headache, myalgia, maculopapular rash
Gram-negative, facultatively anaerobic rod with bipolar staining
Member of Enterobacteriaceae
Zoonotic disease
Enormous historic importance
Yersinia pestis
How does bubonic plague present clinically? How is it transmitted?
incubation period of <7 days after FLEA BITE; high fever, painful inflammatory swelling of lymph nodes; high mortality if untreated
How does pneumonic plague present clinically? How is it transmitted?
incubation period of 2-3 days after AEROSOL EXPOSURE; initially headache, malaise and pulmonary signs; high mortality in untreated
How do you make a lab diagnosis of Yersinia?
culture a sample of blood, bubo aspirate, sputum
What are the natural hosts for Yersinia pestis? How is it transmitted?
rats, squirrels, rabits; flea bite transmission
What is the drug of choice for plague?
streptomycin
**doxycycline could be used alternatively
molds that invade stratum corneum of skin or other keratinized tissues
dermatophytes
3 major genera of dermatophytes
Trichophyton
Microsporum
Epidermophyton
What are the following?
Tinea pedis Tinea cruris Tinea corporis Tinea capitis Onchomycosis
Tinea pedis: athletes foot Tinea cruris: jock itch Tinea corporis: infection of arm, legs, trunk Scalp ringworm infection of nails
There are anthrophilic, zoophilic, and geophilic species of dermatophytes. Which species cause chronic, relatively noninflammatory infections and are difficult to cure? Which species cause profound host reaction, high inflammatory lesions, and respond well to therapy
anthropophilic; zoophilic/geophilic
How do you diagnose dermatophyte infection?
take a sample of the scraping or clipping and dissolve the tissue with KOH, examine microscopically for hyphae
you can also culture the scrapings, but it takes weeks
What do you use to treat dermatophytes?
topicals for locolized infections, azoles or terbinafine
oral agens for more extensive infection, itraconazole, fluconazole, terbinafine
What is pityriasis (tinea) versicolor?
it is caused by Malassezia furfur (budding yeast like cells) which cause small hypo or hyper-pigmented macules (depending on skin color)
What does pityriasis versicolor look like on a KOH mount?
spaghetti and meatballs
yeast + hyphal elements
How do you treat pityriasis versicolor?
topical azoles or selenium sulfide shampoo
oral azoles for widespread infection
Classic infection follows traumatic inoculation of soil or vegetable matter; termed “rose gardener’s disease”
Small nodule at site of inoculation; may ulcerate
Secondary nodules along lymphatics that drain primary lesion
Lymphocutaneous sporotrichosis
What is the dimorphic fungus responsible for lymphocutaneous sporotrichosis?
Sporothrix schenckii
Why is lymphocutaneous sporotrichosis considered “rose gardener’s disease?”
because sporothrix schenckii grows on soil, plants, and decaying vegetation
**seen w florists, rose gardener’s, greenhouse workers
What do you use to treat sporotrichosis?
itraconazole
Localized, chronic, granulomatous process involving cutaneous and subcutaneous tissues
Multiple granulomas and abscesses containing masses of hyphae
Abscesses drain through skin; may extrude granules of hyphae
May destroy muscle and bone locally
mycetoma
What causes mycetoma?
multiple filamentous fungi: Curvularia, Fusarium, Exophiala, etc
What will you see in the exudate of mycetoma?
grains or granules
What is the only definitive treatment for mycetoma?
amputation
