Week 1 Thursday - Diebel - Bacterial Skin Infections

Question 1

Anatomical Diagnosis:
Differential Diagnosis:
Etiologic Diagnosis:

Answer 1

Anatomical Diagnosis: Based solely on the signs and symptoms (patient history)

Differential Diagnosis: Based on a consideration of the number of agents that are known to cause the disease in a particular anatomical location

Etiologic Diagnosis: Exact ID of the disease causing microorganism.

Question 2

What are the two antimicrobial peptides on the surface of the skin discussed in class?

Answer 2

Defensins and cathelicidans

Question 3

What, on the skin, breaks down peptidoglycan?

Answer 3

Lysozymes

Question 4

Major epithelial defense mechanisms (against bacteria).

Answer 4

Dry outermost layer
Antimicrobial peptides on surface
Low pH of sebum
Low pH, high salt content of sweat
Lysozymes
resident phagocytes in epidermis
normal flora that compete for colonization

Question 5

Doctor word for general acne

Answer 5

Folliculitis, infection of the hair follicle

Question 6

Doctor word for clogged pore

Answer 6

Comedo

Question 7

Doctor words for ruptured lesions on skin surface and for ruptured lesions in the deeper layers.

Answer 7

Pustule or papule.

Cyst.

Question 8

Impetigo. What is it and how is it thought to arise?

Answer 8

Superficial bacterial skin infection with peeling, crusty, honey-colored scabs. may be initiated by Streptococcus pyogenes, which makes way for Staphylococcus aureus.

Question 9

Most common infectious agent of the skin and surgical wounds? Presents clinically as: (five localized skin/subcutaneous infection examples from class)

Answer 9

Staphylococcus aureas. Impetigo, cellulitis, folliculitis, furuncles, carbuncles.

Question 10

Three main colonizing virulence factors of Staph. aureus:

Answer 10

Protein A: binds the Fc (constant) domain of IgG (antibody)
Coagulase: forms fibrin coat around the organism
Hemolysins and leukocidins: destroy RBC and WBC, respectfully

Question 11

Doctor word for pus-filled

Answer 11

Purulent.

If you say ‘puss-y’ you WILL be expelled.

Question 12

Three main ‘deep tissue’ virulence factors of Staph. aureus:

Answer 12

Hyaluronidase: breaks down connective tissue
Staphylokinase (lyses formed clots)
Lipase (breaks down fat)

Question 13

Two diseases associated with S. aureus exo-toxin production

Answer 13

Toxic shock syndrome. Super antigen promotes excessive cytokine release.

Scalded skin syndrome. Exfoliative toxins ET-A and ET-B diffuse systemically, epidermis separates and skin sloughs off.

Question 14

Localized skin/subcutaneous infections of Streptococcus pyogenes (three clinical examples from class):

Answer 14

Impetigo (exotoxin mediated), erysipelas, cellulitis

Question 15

Toxin-mediated clinical presentations of S. pyogenes (2 from class):

Answer 15

Toxic shock syndrome, necrotizing fasciitis.

Question 16

Deep tissue invasion of S. pyogenes from skin infections can lead to ____ but not ____.

Answer 16

Glomerulonephritis but not Rheumatic fever

Question 17

Purpose of the catalase test:

Answer 17

distinguishes aerobic and facultative anerobic (like staph, micrococcus) from anerobic (like strep).

aerobes can break down H2O2 via catalase.

Question 18

Purpose of the coagulase test

Answer 18

Distinguishes S. Aureus (pos result) from other staph bacteria like S. epidermidis and S. saprophyticus

Question 19

Purpose of the novobiocin sensitivity test:

Answer 19

S. saprophyticus (resistant)
vs
S. epidermidis (sensitive)

Question 20

Presentation of cellulitis

Answer 20

Fast-spreading infection in the dermis: pain, tenderness, swelling, warmth, erythema.

Question 21

Presentation of SSSS (Staph scalded skin syndrome)

Also, what exotoxins cause it?

Answer 21

Erythema (dermis) visible under shedding epidermis. Caused by exfoliative toxins ET-A and ET-B.

Question 22

What type of bacteria cause gas gangrene and cellulitis? How is an infection of this bacteria typically treated?

Answer 22

Clostridium perfringens, anerobic bacteria that form spores. They require damaged tissue to enter the skin. Treated via surgical removal or hyperbaric oxygen. Antibiotics work only in weak infections

Question 23

Bacteria responsible for “Hot tub infections” (a type of folliculitis)

Answer 23

Pseudomonas aeruginosa

Question 24

Two examples of arthropod-borne bacterial infections

Answer 24

Borrelia burgdoferi (lymes disease)
Rickettsia rickettsii (RMSF)

Question 25

Rocky mountain spotted fever (RMSF) rash starts where and spreads to where? What kind of rash is it?

Answer 25

starts: hand and feet
spreads: trunk of extremity

maclulopapular rash: flat, red area covered with small, confluent bumps.

Question 26

Name two obligate intracellular bacterial parasites from class that need host ATP

Answer 26

Chlamydiae and rickettsiae.