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Microbio Gram Pos > Staphylococci > Flashcards

Staphylococci Flashcards

1
Q 
General characteristics of Staph
Morphology
Hemolysis
O2 preference
Agar
Presentation
Source
A

Clusters
Hemolytic patterns not useful
Facultative
Grows on mannitol salt agar, fermenting it and turning it yellow
Usually causes acute infection, but chronic in bones
Most infections are autochthonous

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2
Q

Reservoir for Staph aureus

A

Nose / skin. 1/3 of population are carriers.

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3
Q

Transmission of Staph aureus

A

Direct contact (mainly), endogenous, airborne, food poisoning

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4
Q

Does Staph aureus or Coag-Neg Staph cause more severe infections?

A

Staph aureus

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5
Q

Best virulence marker for Staph aureus

Function

A

Coagulsase

Converts fibrinogen –> fibrin, which protects against phagocytosis

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6
Q 
Function of the following Staph aureus antigens:
Cell wall
Teichoic acid
Protein A
Exotoxins (mechanism)
Leukocidins
A

Cell wall - antiphagocytic
Teichoic acid - adherence via binding to fibronectin
Protein A - inhibits Ab-mediated clearance by phagocytes. Binds Fc portion of IgG.
Exotoxins (mechanism) - mediated by plasmid-lysogenic phages
Leukocidins - Kill white cells. Ex: Panton-Valentin Toxin

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7
Q

Panton-Valentin Toxin

A

Soft-tissue toxin of community acquired MRSA. Forms pore –> lysis of RBCs and PMNs. Allows Staph aureus to penetrate into tissues.

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8
Q

Prototypical lesion of S aureus

A

Abscess

If you see pus in a skin lesion, it’s most likely Staph aureus

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9
Q

Most common infections w/ Staph

A

Skin infections

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10
Q 
Furuncle / Boil
Caused by
Characteristics
Tx
Risks
A

Caused by Staph aureus

Large abscess in skin / subQ. Drain pus and pack w/ gauze. High risk of bacteremia / metastatic infection

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11
Q

Carbuncle
Caused by
Characteristics
Location

A

Caused by S aureus (bacteremia)

When furuncles coalesce and dive deeper into skin. Usually on back of neck.

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12
Q 
Impetigo
2 causes
Characteristics
Location
Population
A

Caused by Staph aureus and GAS

Superficial skin infection. Pus. Mainly affects face / limbs of young children

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13
Q

Cellulitis
Cause
Characterstics
Tx

A

Caused by S aureus
Deeper infection of dermis and subcutaneous fat.
Tx w/ systemic AB’s

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14
Q

Folliculitis
Cause
Tx

A

Caused by S aureus

Resolves on own

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15
Q 
Staph Scalded Skin Syndrome
Cause
Population
Mechanism
Mortality?
A

Caused by S aureus.
Most common in kids.
Caused by exfoliative toxin → splits intercellular connections in stratum granulosum → desquamation. Low mortality.

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16
Q

Staph aureus bacteremia
Cause
Risks

A

May be caused by IV catheter.
May lead to sepsis.
Mortality of nosocomial Staph infection is 25%.
25% chance of endocarditis as well

17
Q

Staph aureus pneumonia

Risk factors

A

Common in pxs w/ bacteremia, endocarditis, or on ventilator. Risk in very young, elderly, post-viral infection, CF, COPD

18
Q

Osteomyelitis
Cause
Population and location

A

Staph aureus is #1 cause of osteomyelitis in children, mainly affecting long bones. Commonly affects spine / axial bones in adults. Bones may contain pus.

19
Q

1 cause of ventilator associated pneumonia (VAP)

A

Staph aureus

20
Q 
Exotoxin food poisoning
Sxs
Timing
Risks
Common foods
A

“Enterotoxins” cause inflammation of GI tract, vomiting, diarrhea, usually in first 2-4 hrs after consumption. Sxs last 24 hrs. Fever is rare.
Self-limiting, rarely lethal.
Most commonly grows in ham, potato-salad, and custard-filled pastries when left at room temp.

21
Q 
Staph Toxic Shock Syndrome
Antigen
Sxs
Comparison to Strep TSS
Cause
Risk
Tx
A

TSST-1 is super-antigen
Diffuse erythema, desquamation of skin, hypotension, fever.
Not nearly as virulent as Strep TSS.
•Most often due to hyperabsorbant tampon use. 5% of women carry Staph aureus in vagina.
Low mortality. Infection ends when tampon is removed.
•Rare shock via post-surgical infection has high mortality.

22
Q

General characteristics of Coag-Neg Staph
#1 cause of what?
Comparison to S aureus
Presentation

A

1 nosocomial pathogen in developed world.

Less virulent than Staph aureus. Does NOT cause shock.
Causes indolent, chronic infections
May take months / years to present.

23
Q 
Staph epidermidis
Coagulase?
Reservoir
Hemolysis
Agar
Oxygenation
Transmission
A

Coag-Neg
Normal microbiota on skin and mucus membranes
Non-hemolytic
Grows on mannitol salt agar but does not ferment.
Facultative
Mainly transmitted via own flora during medical implantation. Can be direct contact.
Causes 90% of Coag-Neg Staph infections.

24
Q

Staph saprophyticus
Reservoir
Main disease

A

Colonizes skin and urethra

Causes UTI’s in newly sexually active females

25
Q

Diseases of Coag-Neg Staph

A

SSI’s
Folliculitis
Medical devices - biofilms form on IV catheters, prosthetic heart valves, artificial joints, LVAD, breast implants, cranial shunts, and artificial lens.

26
Q

Virulence factors of Coag-Neg Staph

A

Adhesins bind fibronectin for adherence.

Biofilms prevent phagocytosis.

27
Q

AB resistance and tx for Coag-Neg Staph

A

Often resistant to beta-lactams and methicillin. Use vancomycin.

28
Q

Susceptible hosts to Staph

A

Babies, neutropenia, IV catheters, IV drug users, diabetics, burn pxs, post-op, implanted medical devices

29
Q

3 most common causes of cryptogenic bacteremia of healthy adults

A

Staph aureus
Meningocccus
GAS

30
Q 
General treatment for Staph
If resistant?
If allergic?
Soft tissue infections?
Abscess?
Bacteremia / endocarditis?
A

•Penicillin if susceptible (rare)
•Methicillin (nafcillin or oxacililn) or dicloxiacillin if penicillin resistant. Cephalosporins / carbapenems may also be used.
Clindamycin if allergic to penicillin.
•Vancomycin if methicillin-resistant.
•Linezolid or Daptomycin if vancomycine-resistant. Daptomycin does NOT work to tx pneumonia. Linezolid does NOT work for bacteremias.
•Soft tissue infections – use clindamycin, TMP-sulfa, or minocycline
•Abscesses – main tx is incision / drainage. AB may be used depending on site.
•Bacteremia and endocarditis require multiple-week IV AB therapy

Microbio Gram Pos (11 decks)

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