Exam #8: SSTI III Flashcards
List the characteristics of Clostridium.
Gram (+) rods
Spore-forming
*can last for years & resistant to heat, desiccation, & disinfectants
What SSTIs are caused by C. perfringens? What other diseases are caused by C. perfringens?
Gas Gangrene (Clostridial myonecrosis)
Also,
- Cellulitis
- Fasciitis
- Suppurative myositis
- Myonecrosis i.e. Gas gangrene
What toxins are associated with C. perfringens?
- Alpha-toxin that destroys cell membranes by lysing cells
- Also, note that C. perfringens growth is accompanied by large amounts of hydrogen and carbon dioxide gas (that can be seen on X-ray)
When is C. perfringens Gas Gangrene most common?
Traumatic wound
Surgical post-op
*Note, this is a wound infection accompanied by gas production or “crepitations”
Describe the progression of Gas Gangrene.
1) Starts as cellulitis
2) Progresses to suppurative myositis
4) myonecrosis (painful, rapid destruction of muscle tissue)
3) Gas gangrene
*Note that this rapid spread is mediated by Alpha-toxin associated with C. perfringens
How is C. perfringens diagnosed & how is it treated?
- Clinical observations are key!
- Microscopic detection of gram positive rods WITHOUT leukocytes (killed by the alpha-toxin)
- Immediate surgical debridement & high dose PCN therapy
List the characteristics of C. tetani.
Gram (+) rod
Spore forming
Strict anaerobe*
How is C. tetani introduced into the body?
- Wound puncture
- Umbilical stump infection
How does C. tetani present?
“Spastic paralysis” caused by tetanospasmin mediated prevention of the release of inhibitory neurotransmitters (Glycine & GABA)
*vs. Flaccid Paralysis in Botulinsm
What toxins are produced by C. tetani?
Tetanospasmin
Heat labile Neurotoxin
What is the mechanism of Tetanospasmin?
Inactivates proteins that control the release of inhibitory neurotransmitters and results in spastic paralysis
What is risus sardonicus?
Lock jaw
What is opisthotonic posturing?
Involvement of the spinal musculature in the newborn infected with Tetanus (omphalitis)
How is C. tetani diagnosed?
Clinical presentation
- Cannot be cultured b/c it is a strict anaerobe
*Mostly seen in the elderly population esp. those that have NOT maintained their booster & like to garden
How is C. tetani infection treated?
- Debridement of the primary wound
- Metronidazole
- HTIG (Human tetanus immunoglobulin i.e. anti-toxin)
How is C. tetani prevented?
Vaccination (Tetanoid toxin)
Boosters
List the characteristics of the mycobacterium.
- Acid fast
- Lipid-rich cell wall (mycolic acid)
- Resistant to disinfectants, detergents, antibiotics…etc.
- Slow-growing
*Weakly Gram (+) but not visualized very well
What diseases are associated with Mycobacterium?
TB
Leprosy
How much of the world’s population is infected with MTB?
1/3, mostly in Saharan Africa
Describe the pathogenesis of MTB.
- Primary infection is pulmonary
-
What is Pott’s disease?
Pott’s Disease is a type of bacterial osteomyelitis that progresses slowly over months
- Occurs most in undeveloped countries & immunocompromised
- Occurs via respiratory route & hematogenous spread
- Most commonly seen in thoracic and lumbar vertebrae
What is a gibbus deformity?
Abnormal kyphosis of the lower thoracic spine that is associated with Pott’s Disease
How is Pott’s Disease diagnosed?
- Hx of travel or recent immigration to the US
- Slowly progressing back pain
- “Gibbus deformity”
- Positive PPD
- Evidence of Mycobacterium in aspirate or biopsy of spinal lesion (granuloma)
How is MTB treated?
RIPE (long duration)
- Rifampin
- Isonidazole
- P
- Ethambutol
*6 months of treatment
What organism causes Leprosy?
Mycobacterium leprae
What are the two reservoirs for Mycobacterium leprae?
Humans
Armadillos
What cells are targeted by Mycobacterium leprae?
Macrophages and Schwann cells
What are the two different stages of M. leprae?
Tuberculoid (Th1) response
Lepromatous (Th2)= classic
What is the difference between Tuberculoid and Lepromatous?
Lepromatous= antibody production that is NOT helpful in eradicating the disease–>Hansen’s Disease
- Th2 response & antibody
List the characteristics associated with Tuberculoid (Th1) leprosy.
- Few lesions with flat centers
- Few acid fast rods
- DTH reaction to lepromin (Th1) like PPD but for leprosy
- Normal immunoglobulin levels
- No Erythema nodosum
List the characteristics of Lepromatous (Th2) leprosy.
- Many lesions with nodules & nerve involvement
- Many acid fast rods
- No reactivity to lepromin (Th2)
- Hypergammaglobulinemia
- Erythema nodosum usually present
How is Leprosy diagnosed?
- Lepromin test= M. leprae injection similar to PPD
- Culture is impossible
- Must take a biopsy and perform acid fast staining
Which type of leprosy is NOT associated with a positive skin test?
Lepromatous (Th2)
What are Nocardiosis and Actinomycosis?
Filamentous bacteria that cause skin infection
What are the different presentations associated with Nocardia?
Bronchopulmonary Disese Cutaneous infections - Mycetoma - Lymphocutaneous infections - Chronic ulcerative lesions - Subcutaneous abscesses - Cellulitis
List the characteristics of Nocardia.
Gram positive rod
Weakly acid fast*
Filamentous
Forms aerial hyphae in culture (furry stuff that grows off the plate)
*Resembles fungi/ hyphae
What is mycetoma?
- Skin infection caused by Nocardia that is usually seen in the lower limb, and painless
- Wound on the foot gets infected with Nocardia
How is Nocardia diagnosed?
- Hx (environment)
- Direct examination of clinical specimen–>weakly acid fast*
Note that this can be confused with Sporothrix schenckii (fungal infection)
How does Actinomycosis differ from Nocordia?
- Not acid fast
- “Molar” appearance on plate, NOT aerial hyphae
List the characteristics of Actinomyces.
- Filamentous bacteria that resembles fungi
- Strict anaerobe
- Normal flora in respiratory tract
- Associated with dental work–> lump on the cervicofacial region
What is a hallmark of Actinomycoses?
Sulfur granules–colonizes of the organism that look like grains of sand
How is Actinomycosis diagnosed?
- Direct examination
- Differentiate from Nocordia with the acid fast stain
How is Actinomycosis treated?
PCN
What is Acne vulgaris?
Common disorder of the pilosebaceous unit
What are the four key elements of acne vulgaris?
1) Follicular epidermal hyperproliferation
2) Excess sebum production
3) Inflammation
4) Presence and activity of Propionibacterium acnes
What organism is associated with acne vulgaris?
Propionibacterium acnes
List the characteristics of Propionibacterium acnes.
- Small anaerboic Gram-positive rod
- Part of the normal flora
- Stimulates an inflammatory response that some people have
How is acne treated?
1) Benzoyl peroxide (exfoliation)
2) Topical antibiotics
3) Oral antibiotics (doxycyline)
4) Isotretenoin
What is gingivitis?
Inflammation of the gums that is reversible
What is periodontitis?
Chronic inflammatory disease that includes gingivitis along with loss of connective tissue and bone support for the teeth that is irreversible
What are the causative organisms of gingivitis and periodontitis?
Bacteria in dental plaque primarily by Gram-negative anaerobic flora, including:
- Poryphyromonas gingivalis
- Treponema denticola
What is the dominant organism that causes dental caries?
S. mutans (viridans strep)
-acid from these organisms lead to tooth decay
