Skin III

Question 1

describe type I: polymicrobial necrotizing fasciitis/myonecrosis

Answer 1

• type I: polymicrobial
  
  • due to both aerobic and anaerobic bacteria
  • common following intra-abdominal surgery, in diabetics and in intravenous drug users

Question 2

type II necrotizing fasciitis/myonecrosis is caused by ____

Answer 2

type II necrotizing fasciitis/myonecrosis is caused by S. pyogenes

Question 3

describe the onset of necrotizing fasciitis/myonecrosis

Answer 3

sudden onset (as short as ~4 hours)

Question 4

describe Clostridium perfringens

Answer 4

Question 5

describe the virulence factor of Clostridium perfringens

Answer 5

• exotoxins:
  
  • alpha toxin (lecinthinase)

Question 6

C. perfringens requires ___, ____ and ____ conditions in order to grow

Answer 6

C. perfringens requires damaged, dead tissue and anaerobic conditions in order to grow

Question 7

the culture of C. perfringens on blood agar would show a characteristic ___ zone of hemolysis

Answer 7

the culture of C. perfringens on blood agar would show a characteristic double zone of hemolysis

beta-hemolysis surrounded by a larger zone of alpha hemolysis

Question 8

describe the purpose of culturing C. perfringens on egg-yolk agar (EYA)

Answer 8

lecithinase from C. perfringens forms opaque colonies on EYA

• lecithinase
  
  • lecithinase degrades lecithin to insoluble diglycerides; positive reaction is white opaque zone around colonies
• lipase test:
  
  • lipase degrades triglycerides into glycerol and FFAs
  • positive reaction is a pearly, iridescent sheen on agar and colonies

Question 9

the Nagler test is used to differentiate among _____

Answer 9

the Nagler test is used to differentiate among lecithinase-positive Clostridium spp.

Question 10

describe the purpose of reverse CAMP test

Answer 10

Question 11

describe crepitus

Answer 11

Question 12

describe the clinical manifestations of staphylococcal scalded skin syndrome

Answer 12

• clinical:
  
  • SSSS usually starts with fever and widespread redness of the skin
  • within 24-48 hours fluid-filled blisters form
  • these rupture easily, leaving an area that looks like a burn

Question 13

describe the epidemiology of scalded skin syndrome

Answer 13

• occurs mostly in children younger than 5, particularly in neonates
• lifelong protective antibodies against staphylococcal exotoxins are usually acquired during childhood

Question 14

in scalded skin syndrome, staphylococcal spp. release 2 ___ that bind to ___ and break it up

Answer 14

in scalded skin syndrome, staphylococcal spp. release 2 exotoxins that bind to desmoglein-1 and break it up

Question 15

the most common cause of erythrasma is ____

Answer 15

the most common cause of erythrasma is Corynebacterium minutissimum

Question 16

in erythrasma, ____ invade the ____

Answer 16

in erythrasma , Corynebacterium minutissimum invade the upper third of the stratum corneum

Question 17

in erythrasma, infected skin glows ____

Answer 17

in erythrasma , infected skin glows coral-red under UV

the coral-red fluorescence is secondary to the production of porphyrin (heme metabolism)

Question 18

favorable conditions for C. minutissimum are ___ and ___

which locations of the body have these conditions?

Answer 18

favorable conditions for C. minutissimum are heat and humidity

foot, groin, armpits, skinfolds, vaginal opening and the anus

Question 19

erythrasma, caused by ___, affects mostly adults, especially those with ___ and those living in ____

Answer 19

erythrasma, caused by C. minutissimum, affects mostly adults, especially those with diabetes and those living in the tropics

Question 20

erysipeloid is an ___ disease that is caused by ____

Answer 20

erysipeloid is an occupational disease that is caused by Erysipelothrix rhusipathiae

Question 21

describe the clinical presentation of erysipeloid

Answer 21

Question 22

risk factors for erysipeloid is contact with animals such as ___ and ___

Answer 22

risk factors for erysipeloid is contact with animals such as swine and fish

Question 23

one of the pathogenetic mechanisms of erysipeloid is that it can cause ____

Answer 23

one of the pathogenetic mechanisms of erysipeloid is that it can cause endocarditis

Question 24

in erysipeloid, the lesion has a ___ color with ___ borders

Answer 24

in erysipeloid, the lesion has a violet color with well-defined borders

Question 25

describe the 3 important virulence factors of anthrax

Answer 25

* **edema toxin** * adenylate cyclase activity (fluid accumulation) * **lethal factor** * stimulate macrophages to release pro-inflammatory cytokines * **protective antigen** * most immunogenic

Question 26

the most immunogenic virulence factor of anthrax is \_\_\_\_

Answer 26

the most immunogenic virulence factor of anthrax is **the protective antigen**

Question 27

edema toxin, formed by anthrax, causes an increase in ____ activity which leads to \_\_\_\_

Answer 27

edema toxin, formed by anthrax, causes an increase in **adenylate cyclase activity** which leads to **fluid accumulation**

Question 28

lethal factor, found in anthrax, stimulates ___ to release \_\_\_\_

Answer 28

lethal factor, found in anthrax, stimulates **macrophages** to release **pro-inflammatory cytokines**

Question 29

the capsule formed by anthrax has a ____ composition

Answer 29

the capsule formed by anthrax has a **polypeptide (glutamic acid)** composition

Question 30

cutaneous anthrax has a ___ mortality rate GI anthrax has a ____ mortality rate inhalational anthrax has a ___ mortality rate

Answer 30

cutaneous anthrax has a **20%** mortality rate GI anthrax has a **50%** mortality rate inhalational anthrax has a **100%** mortality rate

Question 31

describe the clinical presentation of cutaneous anthrax absence of ___ is characteristic of anthrax lesions

Answer 31

initially: **itchy papule** papule becomes a **hemorrhagic vesicle** blister forms a hard, **painless, blue-black leathery scab** absence of **pain** is characteristic of anthrax lesions