EXAM 5 Skin and Soft Tissue Infections Dr. Cluck

Question 1

Know for the EXAM

Answer 1

common organism
how to treat them
MRSA activity (1-2 questions)

Question 2

Which organisms are part of the normal flora of the skin?

Answer 2

GRAM-POSITIVE
-Coagulase-negative staphylococci
-Corynebacteria (some species are more pathogenic than others, for the most part it is not)
-Propionibacteria
-Streptococci

GRAM-negative (like E.coli) is NOT common on the skin

Fungal
-Candida
-Malassezia sp.

Question 3

Types of SSTIs

Answer 3

Acute superficial infections
-Impetigo
-Erysepalis
-Lymphangitis

Cellulitis (deeper)

Necrotizing Infections (even deeper, EMERGENCY)
-Fascitis
-Gangrene

Animal and human bites

Question 4

How does the MLS(B) Staph strain conduct their resistance? To which drugs?

Answer 4

resistant to Macrolides and Clindamycin (lincasomide)
-they bind to the 50S ribosomal subunit and inhibit protein synthesis

Resistance through methylation of the ribosomal target site (erm)

Question 5

The msrA Staph strain is resistant to which drug? Explain the mechanism.

Answer 5

Macrolides

throws out the drug through the efflux pump

Question 6

The inuA Staph strain is resistant to which drug? Explain the mechanism.
(rare)

Answer 6

Lincosamides

-inactivation through chemical modification

Question 7

What induces the MLS(B) resistance?

Answer 7

-Constitutive resistance: the rRNA methylase is always produced, the background stays the same (no zone)

-drug induced: in the presence of Erythromycin (strong inducer) or Clindamycin (weak inducer)

with no resistance: large and round-shaped zone

Question 8

Which test is used to check for MLS(B) resistance?

Answer 8

D-test

if positive (ICR: induced clindamycin resistance) don’t use Clindamycin - it indicates that resistance may develop (since it was induced during the test by erythromycin)

Question 9

Which agents are susceptible to Community-Acquired-MRSA?
!!!

Answer 9

Vancomycin (IV)
Linezolid (oral, IV)
Daptomycin (IV)

TMP/SMX (oral)
Clindamycin (oral)
Tetracyclines (Doxycycline, Minocycline) (oral)
Fluoroquinolones (oral)

Question 10

Which agents are susceptible to hospital-acquired MRSA?
!!!

Answer 10

Vancomycin
Linezolid
Daptomycin

Question 11

Common IV drugs for MRSA

Answer 11

Vancomycin
Linezolid
Daptomycin

Ceftaroline (5th)
Televancin
Tigecycline/erava/omada
Oritavancin/dalbavancin !!!

Question 12

MOA Dalbavancin/Oritavancin

Answer 12

long-acting lipoglycopeptides

MOA: hybridized version of daptomycin and vancomycin

-interferes with peptidoglycan cross-linking (binds to D-ala-D-ala terminus of stem peptides

Vancomycin (blocks the enzyme transglycosylase from incorporating into the cell wall)
Daptomycin (integrates into the cell wall, and forms holes -> K+ leakage)

Question 13

Dosing Dalbavancin and Oritavancin

Answer 13

Dalbavancin:
1000 mg on day 1 and 500 mg on day 8 (studies have shown 1500 mg once is fine)

Oritavancin: 1200 mg once

both have a huge half-life (187h and 393h)

Question 14

Dalbavancin’s/Oritavancin only FDA indication is…

!!! EXAM Q

Answer 14

for Skin and Soft Tissue infections !!!

only approved for a single dose

Question 15

How long is a patient therapeutic with one single dose of Dalbavancin?

Answer 15

about 14 days

equivalent to 14 days of Vancomycin

Question 16

When are two or more doses of Dalbavancin/Oritavancin required?

!!!

Answer 16

Osteomyelitis

1500 mg at day 1
1500 mg at day 8

-bacteremia from SSTI

-dose adjustment needed in renal-impaired patients

Question 17

Dalbavancin is active against which bacteria? (gram (+) or (-)
No activity against…

Answer 17

gram-positive !!! doesnt cover gram-negative

on the EXAM if there is a gram-negative -> add Pip/tazo, Amox/Clav, Ceftriaxone, Ceftazidime, Cefepime; (Carbapenem, FQ, Tetracycline, Aminoglycoside also cover gram-negatives)

no activity against Vancomycin-resistant enterococci (VRE)

Question 18

Which drug should be used for an allergic reaction to Dalbavancin?

Answer 18

Benadryl

in general, Dalbavancin is safe in patients who state to have an allergy to Vancomycin

Question 19

The difference in administration between Dalbavancin vs Oritavancin

Answer 19

Dalbavancin is 1h and compatible with normal saline

Oritavancinc is 3h and in D5W
-> new formulation Kimyrsa is 1h and compatible with normal saline but expensive (6400$)

Question 20

Dalbavancin vs Oritavancin - Coverage and MOA differences

Answer 20

multiple MOA (inhibits transglycosylation, transpeptidation, and disruption of the membrane)

-more like Daptomycin (bacteriocidal)
-activity against VRE

1200 mg once
(subsequent doses are 800 mg)

Question 21

Do Dalbavancin and Oritavancin require therapeutic dose monitoring?

Answer 21

No

Question 22

The SOLOI and SOLOII trial showed what…

Answer 22

compared 1200 mg single dose of Oritavancin with 7-10d of Vancomycin BID in adults with ABSSSI and MRSA infection

Question 23

What are the contraindications of Oritavancin

Answer 23

-use of unfractionated heparin for 48 hours after giving Oritavancin -> interferes with aPTT

-interferes with coagulation tests (prolongs aPTT and PT/INR)

-concomitant use with warfarin (increases warfarin)

Question 24

Side effects of Telavancin
(not recommended)

Answer 24

-increases serum creatinine (nephrotoxic)
-prolonged QTc
-foamy urine

the only benefit to Vancomycin:
-1x daily dosing
-doesn’t require therapeutic monitoring

Question 25

Telavancin Indication

Answer 25

HAP/VAP

in susceptible isolates of Staph aureus and other drugs have failed

Question 26

Which drug should not be used for Pneumonia?

Answer 26

Daptomycin
pulmonary surfactant !!!

Question 27

Concerns of Linezolid and why Tidezolid is actually not better

Answer 27

-weak MAOI -> hypertensive crisis
-serotonin syndrome
-myelosuppression, less RBC production from bone marrow (especially after 14 days)
-thrombocytopenia

studies have shown better outcomes, but it was probably underdosed

Question 28

Pathogens associated with SSTIs

Answer 28

-Injection drug use: Staph aureus !!! Clostridium, E. corrodens, Group A Strep

-Saltwater injury: Vibriovulnificus

-Freshwater injury: Aeromonashydrophila

-Fishmonger: Erysipelothrixrhusiopathiae (intrinsic resistant to Vancomycin), Streptococcus iniae

-Hot tubs: Pseudomonas aeruginosa

Question 29

The only place where AUC is validated based on the guidelines is..-

Answer 29

invasive MRSA infection (SSTI is not considered invasive)

for usual MRSA: through-based monitoring

Question 30

What is the purpose of AUC?
FIY

Answer 30

to ensure safety (make sure to prevent nephrotoxicity)

-AUC doesn’t tell how effective the drug is

Question 31

Which antibiotic can be used for Strep pyogenes?

Answer 31

any ß-lactam works

Question 32

What most often causes Folliculitis?

Answer 32

-S. aureus
-Hot-tub folliculitis is caused by P. aerigonsa

-clogged hair follicle

Question 33

Therapeutic approach for Folliculitis?

Answer 33

-Lesions often resolve spontaneously
-Moist heat (up to 3x/day) can facilitate drainage

Question 34

What is the difference between Furuncles and Carbuncles?

Answer 34

Furuncles
-inflammatory nodules (small abscess)
extending into the subcutaneous tissue
1 pustular opening

VS

Carbuncles
- coalescence of hair follicles which extends into the
subcutaneous fat

more than 1 pustular opening

Question 35

Which organism causes Furuncles?

What is the treatment for Furuncles and Carbuncles?

Answer 35

S. aureus

incision and drainage - “Drainamicin” HaHa

-smaller furuncles, only moist heat may
be needed

-data of a study says there is a benefit when using 7 days of antibiotics (Bactrim)
->use if surrounding cellulitis

Question 36

Which organism causes Impetigo?

Answer 36

S. aureus and S. pyogenes
Contagious (stay at home)

Question 37

A patient presents with a golden crusting sore on the face. Which Skin Tissue Infection is most likely the cause?

Answer 37

Impetigo

Question 38

Which antibiotic is used for Impetigo?

Answer 38

1st line: topical Mupirocin or retapamulin

-oral therapy:
Antistaphylococcal penicillins
Cephalexin
Clindamycin (in case of penicillin allergy)

-OTC triple antibiotic topical (some activity but inferior)

Question 39

Which organism causes Lymphangitis, often after a cat bite?

Answer 39

S. pyogenes (Group A strep)

-DOC is penicillin
-> any ß-lactam works EXCEPT Aztreonam (only active against gram-negatives)

Question 40

A fiery red, tender, painful plaque with demarcated edges is which SSTI?

Answer 40

Erysipelas

Subtype of Cellulits

Question 41

Which organism causes Erysipelas?

Answer 41

S. pyogenes

others are S. aureus (rare), ß-hemolytic strep (GCS, GGS)

Question 42

Which antibiotics are used for Erysipelas?

Answer 42

Penicillin VK

-if MSSA is suspected:
Cephalexin
Antistaphylococcal penicillins (nafcillin, oxacillin)

-in penicillin-allergic patients:
Clindamycin or Erythromycin

Question 43

Which organism causes Cellulitis?

Answer 43

S. aureus and GAS (Group A Strep)

Question 44

How do we differentiate between cellulitis caused by S. aureus and GAS?

Answer 44

S. aureus induced usually also has abscesses
->drain the abscess -> 7 days of some antistaphylococcal therapy (depending on the organism)

GAS: red and inflamed

Question 45

What is a key characteristic of a Cellulitis infection? (patient presentation)

Answer 45

it is unilateral

Question 46

Which disease states mimick Cellulitis?

Answer 46

DVT: red inflamed leg
Venous stasus

Question 47

Which drugs are considered for Cellulitis treatment?

Answer 47

caused by S. aureus and GAS (Group A Strep): we need Staph and Strep coverage

possible options:
-Antistaphylococcal penicillins
-1st gen cephalosporins (Cefazolin)
-Clindamycin

-MRSA active drugs (if MRSA is suspected)
if the patient comes to the ER, we suspect MRSA
go with Vancomycin !!!

Question 48

Characteristics of Necrotizing Fascitis

Answer 48

-Painful, hot, swollen, erythematous, shiny

-Blisters
-Subcutaneous gas
-Tense edema outside area of skin

-medical EMERGENCY
cases of Fournier’s Gangrenes need surgery + Antibiotic

Question 49

What is the difference between Necrotizing fasciitis Type 1 and 2?

Answer 49

Type 1: mixed infection caused by aerobic and anaerobic bacteria (often after surgery or trauma)

Type 2: a monomicrobial infection caused by group
A streptococcus (GAS, MRSA)

Question 50

How is Necrotizing fasciitis treated?

Type I

Answer 50

surgical intervention (debridement) combined with
antimicrobial therapy and physiologic support
-not Antibiotic alone

-should include anaerobic coverage (Pip/tazo, Meropenem, Metronidazole)

for Type I:
-Vanc + Meropenem
-Vanc + Pip/tazo
-Vanc + Cefepime (doesn’t have anaerobic coverage) + Metronidazole

Question 51

How is Necrotizing fasciitis treated?

Type II

Answer 51

cover Staph and Strep

-Penicillin + Clindamycin (Protein synthesis inhibitor, so shuts down toxin production)

-may use Linezolid instead (it has great gram (+) coverage and its MOA is to prevent protein synthesis - so it shuts down toxin production)

Question 52

Which organism commonly causes diabetic foot infections?

Answer 52

Group B Strep !!!

Gram-positive cocci

Question 53

Treatment for diabetic foot infections

Answer 53

-based on severity, many options

-empirically:
Vancomycin + Cefepime
Vancomycin + Pip/Tazo

until we have an isolate to see the organism

Question 54

Which organism is usually causes infection after an animal bite?

Answer 54

-Pasturella multocida !!!
-Capnocytophaga canimorsu !!

also:
-Staph aureus
-Staph intermedius !!! Coagulase positive
-Streptococci spp.
-Bartonella henselae - cat stretch disease
-Anaerobes

FYI: Which organism is coagulase-positive?
Staph aureus

Question 55

Drug of choice for animal bites

Answer 55

Augmentin (Amoxicillin-clavulanic)

(IV version: ampicillin-sulbactam) -> may be used for inpatient

avoid due to poor activity against Pasturella multocida
-cephalexin
-clindamycin
-macrolides (only used for lungs and STI) - wrong answer for SSTI on the EXAM

Question 56

58y with Fournier’s Grangene A1c=14

A. Cefepime + Clindamycin + Linezolid
B. Ertapenem + Vancomycin
C. Pip/tazo + Vancomycin + Linezolid
D. Meropenem + Linezolid

Answer 56

A. the function of Clindamycin is to prevent toxin production via protein synthesis inhibition, Linezolid does the same - so its double drug use
(Reminder: Clindamycin has anaerobic coverage)

B. Ertapenem has holes in coverage: Pseudomonas, Enterococcus, and Acinobacter are not covered (probably its not one of those organisms that causes it but for empiric we want as much coverage as possible)

C. Vancomycin and Linezolid both cover gram (+) Staph - double coverage, don’t need both

D. correct - Linezolid covers gram (+) and inhibits toxin production and meropenem covers gram (-) and anaerobes

most common seen is
Vancomycin for (+) + Meropenem for (-) + Clindamycin (for toxin)

Question 57

Organisms causing infections from a human bite

Answer 57

-Staphylococcus aureus (probably secondary)
-Streptococcus spp.
-Peptostreptococcus
-Eikenella corrodens - most often !!!
-Other anaerobes (rarely B. fragilis)

Question 58

Which organism is usually associated with human bites?

Answer 58

Eikenella corrodens

it is a normal commensal in the mouth