Bacterial Infections of the Skin

Question 2

What 2 subcutaneous skin conditions are caused by Group A strep and spread diffusely? Which condition spreads more deeply and can be associated with lymphadenopathy, fever, and bacteremia?

Answer 2

Erysipelas and cellulitis, cellulitis is deeper

Question 3

What subcutaneous skin condition is a rare but severe and gangrenous complication of Group A strep infection, and gives them the name “flesh eating bacteria”?

Answer 3

Necrotizing fasciitis

Question 4

What condition can occur after Group A streptococcus skin infections (especially with the M49 strain), and is characterized by pain, blood, and protein in the urine?

Answer 4

Post-streptococcal nephritis

Question 5

What kind of bacteria would be cultured from a rheumatic fever or post-strep nephritis skin lesion?

Answer 5

None; the lesions are sterile

Question 6

Describe the morphology of Staphylococci. Are they motile and do they make spores?

Answer 6

Gram(+) cocci that grow in clusters. Non motile, no spores.

Question 7

Describe the role of the capsule, protein A, and coagulase in Staphylococci structure.

Answer 7

capsule: resist phagocytosis
protein A: bind immunoglobulins
coagulase: coagulates plasma & localizes infection

Question 8

What is the reservoir and mode of transmission for Staph aureus?

Answer 8

Reservoir: human nose and skin
Transmission: direct contact or indirect via fomites

Question 9

How would you recognize a Staph aureus bacterium in terms of Gram stain, catalase, and coagulase?

Answer 9

Gram(+), catalase(+), coagulase(+)

Question 10

Describe the functions of the Staph aureus toxins DNAse, enterotoxin, exfoliation, leukocidin, and toxic shock syndrome toxin.

Answer 10

DNAse: break down DNA
enterotoxin: GI irritation
exfoliation: generalized desquamation
leukocidin: kill WBCs
TSS toxin: shock

Question 11

Name 2 broad categories of Staph aureus virulence factors.

Answer 11

Structural features (protein A, capsule) and Toxins (coagulase, protein A, enterotoxin, exfoliatin, leukocidin, TSS toxin)

Question 12

What is the major reservoir and method of infection associated with Staph epidermidis?

Answer 12

Reservoir: human skin

Method of Infection: infect piercings or indwelling plastic medical devices

Question 13

Describe the properties of Staph aureus in terms of hemolysis, DNAse, and salt resistance.

Answer 13

β-hemolytic, DNAse positive, salt resistant

Question 14

What term describes a self-limited abscess formed by Staph aureus infection of a superficial sweat gland or hair follicle?

Answer 14

furuncule

Question 15

What is the major reservoir and disease associated with Staph saprophyticus?

Answer 15

human genital tract; cystitis

Question 16

What bacteria are usually responsible for the superficial crusting skin condition of impetigo?

Answer 16

A mix of streptococci and staphylococci

Question 17

What is another name for “scalded skin syndrome,” which looks really bad but is rarely life threatening, and what bacteria is responsible?

Answer 17

Toxic shock syndrome; Staph aureus

Question 18

What term describes a deep skin abscess from Staph aureus infection that tends to spread below the skin and burst out multifocally?

Answer 18

carbuncles

Question 19

What term describes the self-limited abscess formed by Staph aureus infection of a hair follicle near an eye?

Answer 19

stye

Question 20

List 2 steps for the treatment of Staph aureus abscesses.

Answer 20

1. drain/remove abscesses

2. give antibiotics (penicillin, oxacillin, methicillin, vancomycin…and hope it’s susceptible)

Question 21

How can Staph aureus infection be prevented or minimized? Is there a vaccine?

Answer 21

No vaccine; wash hands to reduce bacterial load, cover lesions, try to isolate or remove carriers from situations where they could infect others

Question 22

Describe Staph epidermidis in terms of Gram stain, catalase, coagulase, hemolysis, and novobiocin sensitivity.

Answer 22

Gram(+), catalase(+), coagulase(-), γ-hemolytic (non hemolytic), novobiocin sensitive

Question 23

How can Staph epidermidis infection be prevented or minimized? Is there a vaccine?

Answer 23

No vaccine; change indwelling catheters regularly and use gold or stainless steel jewelry to prevent infections