Exam #8: SSTI III

Question 1

List the characteristics of Clostridium.

Answer 1

Gram (+) rods
Spore-forming

*can last for years & resistant to heat, desiccation, & disinfectants

Question 2

What SSTIs are caused by C. perfringens? What other diseases are caused by C. perfringens?

Answer 2

Gas Gangrene (Clostridial myonecrosis)

Also,

• Cellulitis
• Fasciitis
• Suppurative myositis
• Myonecrosis i.e. Gas gangrene

Question 3

What toxins are associated with C. perfringens?

Answer 3

• 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)

Question 4

When is C. perfringens Gas Gangrene most common?

Answer 4

Traumatic wound
Surgical post-op

*Note, this is a wound infection accompanied by gas production or “crepitations”

Question 5

Describe the progression of Gas Gangrene.

Answer 5

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

Question 6

How is C. perfringens diagnosed & how is it treated?

Answer 6

• Clinical observations are key!
• Microscopic detection of gram positive rods WITHOUT leukocytes (killed by the alpha-toxin)
• Immediate surgical debridement & high dose PCN therapy

Question 7

List the characteristics of C. tetani.

Answer 7

Gram (+) rod
Spore forming
Strict anaerobe*

Question 8

How is C. tetani introduced into the body?

Answer 8

• Wound puncture

- Umbilical stump infection

Question 9

How does C. tetani present?

Answer 9

“Spastic paralysis” caused by tetanospasmin mediated prevention of the release of inhibitory neurotransmitters (Glycine & GABA)

*vs. Flaccid Paralysis in Botulinsm

Question 10

What toxins are produced by C. tetani?

Answer 10

Tetanospasmin

Heat labile Neurotoxin

Question 11

What is the mechanism of Tetanospasmin?

Answer 11

Inactivates proteins that control the release of inhibitory neurotransmitters and results in spastic paralysis

Question 12

What is risus sardonicus?

Answer 12

Lock jaw

Question 13

What is opisthotonic posturing?

Answer 13

Involvement of the spinal musculature in the newborn infected with Tetanus (omphalitis)

Question 14

How is C. tetani diagnosed?

Answer 14

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

Question 15

How is C. tetani infection treated?

Answer 15

• Debridement of the primary wound
• Metronidazole
• HTIG (Human tetanus immunoglobulin i.e. anti-toxin)

Question 16

How is C. tetani prevented?

Answer 16

Vaccination (Tetanoid toxin)

Boosters

Question 17

List the characteristics of the mycobacterium.

Answer 17

• Acid fast
• Lipid-rich cell wall (mycolic acid)
• Resistant to disinfectants, detergents, antibiotics…etc.
• Slow-growing

*Weakly Gram (+) but not visualized very well

Question 18

What diseases are associated with Mycobacterium?

Answer 18

TB

Leprosy

Question 19

How much of the world’s population is infected with MTB?

Answer 19

1/3, mostly in Saharan Africa

Question 20

Describe the pathogenesis of MTB.

Answer 20

• Primary infection is pulmonary

-

Question 21

What is Pott’s disease?

Answer 21

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

Question 22

What is a gibbus deformity?

Answer 22

Abnormal kyphosis of the lower thoracic spine that is associated with Pott’s Disease

Question 23

How is Pott’s Disease diagnosed?

Answer 23

• 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)

Question 24

How is MTB treated?

Answer 24

RIPE (long duration)

• Rifampin
• Isonidazole
• P
• Ethambutol

*6 months of treatment

Question 25

What organism causes Leprosy?

Answer 25

Mycobacterium leprae

Question 26

What are the two reservoirs for Mycobacterium leprae?

Answer 26

Humans | Armadillos

Question 27

What cells are targeted by Mycobacterium leprae?

Answer 27

Macrophages and Schwann cells

Question 28

What are the two different stages of M. leprae?

Answer 28

Tuberculoid (Th1) response | Lepromatous (Th2)= classic

Question 29

What is the difference between Tuberculoid and Lepromatous?

Answer 29

Lepromatous= antibody production that is NOT helpful in eradicating the disease-->Hansen's Disease - Th2 response & antibody

Question 30

List the characteristics associated with Tuberculoid (Th1) leprosy.

Answer 30

- 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

Question 31

List the characteristics of Lepromatous (Th2) leprosy.

Answer 31

- Many lesions with nodules & nerve involvement - Many acid fast rods - No reactivity to lepromin (Th2) - Hypergammaglobulinemia - Erythema nodosum usually present

Question 32

How is Leprosy diagnosed?

Answer 32

- Lepromin test= M. leprae injection similar to PPD - Culture is impossible - Must take a biopsy and perform acid fast staining

Question 33

Which type of leprosy is NOT associated with a positive skin test?

Answer 33

Lepromatous (Th2)

Question 34

What are Nocardiosis and Actinomycosis?

Answer 34

Filamentous bacteria that cause skin infection

Question 35

What are the different presentations associated with Nocardia?

Answer 35

``` Bronchopulmonary Disese Cutaneous infections - Mycetoma - Lymphocutaneous infections - Chronic ulcerative lesions - Subcutaneous abscesses - Cellulitis ```

Question 36

List the characteristics of Nocardia.

Answer 36

Gram positive rod Weakly acid fast* Filamentous Forms aerial hyphae in culture (furry stuff that grows off the plate) *Resembles fungi/ hyphae

Question 37

What is mycetoma?

Answer 37

- Skin infection caused by Nocardia that is usually seen in the lower limb, and painless - Wound on the foot gets infected with Nocardia

Question 38

How is Nocardia diagnosed?

Answer 38

- Hx (environment) - Direct examination of clinical specimen-->weakly acid fast* Note that this can be confused with Sporothrix schenckii (fungal infection)

Question 39

How does Actinomycosis differ from Nocordia?

Answer 39

- Not acid fast | - "Molar" appearance on plate, NOT aerial hyphae

Question 40

List the characteristics of Actinomyces.

Answer 40

- Filamentous bacteria that resembles fungi - Strict anaerobe - Normal flora in respiratory tract - Associated with dental work--> lump on the cervicofacial region

Question 41

What is a hallmark of Actinomycoses?

Answer 41

Sulfur granules--colonizes of the organism that look like grains of sand

Question 42

How is Actinomycosis diagnosed?

Answer 42

- Direct examination | - Differentiate from Nocordia with the acid fast stain

Question 43

How is Actinomycosis treated?

Answer 43

PCN

Question 44

What is Acne vulgaris?

Answer 44

Common disorder of the pilosebaceous unit

Question 45

What are the four key elements of acne vulgaris?

Answer 45

1) Follicular epidermal hyperproliferation 2) Excess sebum production 3) Inflammation 4) Presence and activity of Propionibacterium acnes

Question 46

What organism is associated with acne vulgaris?

Answer 46

Propionibacterium acnes

Question 47

List the characteristics of Propionibacterium acnes.

Answer 47

- Small anaerboic Gram-positive rod - Part of the normal flora - Stimulates an inflammatory response that some people have

Question 48

How is acne treated?

Answer 48

1) Benzoyl peroxide (exfoliation) 2) Topical antibiotics 3) Oral antibiotics (doxycyline) 4) Isotretenoin

Question 49

What is gingivitis?

Answer 49

Inflammation of the gums that is reversible

Question 50

What is periodontitis?

Answer 50

Chronic inflammatory disease that includes gingivitis along with loss of connective tissue and bone support for the teeth that is irreversible

Question 51

What are the causative organisms of gingivitis and periodontitis?

Answer 51

Bacteria in dental plaque primarily by Gram-negative anaerobic flora, including: - Poryphyromonas gingivalis - Treponema denticola

Question 52

What is the dominant organism that causes dental caries?

Answer 52

S. mutans (viridans strep) -acid from these organisms lead to tooth decay