Skin infections

Question 1

Impetigo

Answer 1

Superficial skin infections, most frequently in children

spreading infection confined to the epidermis

Question 2

folliculitis

Answer 2

pyogenic infection in the hair folicles

Question 3

furuncles (boils)

Answer 3

extension of folliculitis (stye)

Question 4

Carbuncles

Answer 4

infection extends to the deeper subcutaneous tissue (chills and fever due to systemic spread with single inflammatory mass

Question 5

erysipelas

Answer 5

spreading infection involving the dermal lymphatics

Question 6

cellulitis

Answer 6

spreading infection when the major factor is the subcutaneous fat layer

Question 7

Abscess formation

Answer 7

folliculitis, boils (furuncles), and carbuncles

Question 8

necrotizing infections

Answer 8

fasciitis and gas gangrene (myonecrosis)

Question 9

Macules

Answer 9

flat and non palpable lesions

Question 10

papules

Answer 10

palpable lesions

Question 11

vesicles

Answer 11

palpable, fluid filled lesions (chiken pox)

Question 12

pustules

Answer 12

palpable and contain pus.

When looking at a slide, you will see an accumulation of neutrophils with serous fluids within or beneath epidermis

Question 13

Bulla

Answer 13

collection of serous fluid and have small numbers of inflammatory cells

Question 14

Characteristics of S. Aureus

Answer 14

gram positive: most resistant of the non spore formers to adverse condition

non motile

facultative anaerobic

catalase and coagulase positive

can grow in 10% NaCl

Abscesses, systemic diseases, food posioning, toxic shock syndrome

Question 15

virulence factors of S. aureus

Answer 15

staphylocococcal toxins (alpha, beta, delta, gamma, and P-V)

exfoliative toxins

enterotoxins

toxic shock syndrome toxins

enzymes: coagulase, catalase, hyaluronidase, fibrinolysin, lipases, nucleases

Question 16

Characteristics of streptococcus

Answer 16

gram + arranged in chains

avoid phagocytosis mediated by capsule, M proteins, C5a peptidase

non motile

facultatively anaerobic

catalase negative

nutritional requirement; complex, need blood or serum enrich media for isolation.

carbohydrate: lancefield groups

M protein: 80 types

Streptolysin O and S

Hyaluronidase, DNASE

Question 17

Skin abscesses, furuncles, and carbuncles

Answer 17

all related to hair follicle

collection of pus within the dermis and deeper skin tissues (pustule)

risk factors: diabetes, immunologic abnormalities and breaches to the skin barrier.

most are caused by infections. may be polymicrobial or monomicrobial. S. aureus occurs in up to 50% cases

TX: small furuncles, warm compresses to help drainage. Incision and drainage. The role of ancillary antimicrobial therapy is unclear.

Question 18

Impetigo (pyoderma, impetigo contagiosa)

Answer 18

contagious superficial infection primarily seen in young children (2-5 years).

poor personal hygiene

purulent with crusting

commonly caused by streptococcus pyogenes either alone or together with staphylococcus aureus

Question 19

non bullous impetigo vesiculopusules with crusting

Answer 19

papules progress to vesicles surrounded by erythema

most frequently observed in children ages 2 to 5 years

usually occurs in warm, humid conditions

risk factors: poverty, overcrowding, poor hygiene, and underlying scabies

GAS and S. aureus are most common causes

impetigo caused by nephrogenic GAS can lead to post streptococcal glomerulonephritis

Question 20

pustular impetigo

Answer 20

intraepidermal vesicles filled with exudate (pus)

crusted lesions

S. aureus, or GAS

seen in exposed areas of the body during the warm, moist weather

Question 21

bullous impetigo

Answer 21

localized staphylococcal scalded skin syndrome

caused by S. aureus of phage group II that produces exofliative toxin A (no cell adhesion)

happens in newborns and young children

culture positive

no nikolsky’s sign

high communicable

Question 22

erysipelas 2 (long and explained)

Answer 22

tender, superficial erythematous and edematous lesions

the infection spreads primarily in the upper dermis and superficial lymphatics (deeper dermis and subcutaneous fat is cellulitis)

mainly affected young and elders. Fiery red (salmon red), advancing erythema

the rash is usually confluent and sharply demarcated rom the surrounding, normal skin.

It is always caused by GAS.

Question 23

Cellulitis: acute inflammation

Answer 23

Redness, induration, heat, and tenderness, the distinction between infected and noninfected area is not as clear

often accompanied by inflammation of the draining lymph nodes

90% of cases are caused by GAS and S. Aureus

In unimmunized children, infection with H. Flu type B

cellulitis associated with bites or scratches from cats or dogs (p. multocida)

all develop rapidly (24 to 48 hrs) from minor injury to severe speticemia

elevation of the affected area and empiric antibiotic therapy

Question 24

Necrotizing infections of the skin and fascia

Answer 24

common features: extensive tissue destruction, throbosis of blood vessels, bacteria spreading along fascial planes, and unimpressive infiltration of inflammatory cells

necrotizing fasciitis is a deep seated infection of the subcutaneous tissue leading to destruction of fascia and fat but may spare skin

Question 25

Type 1 necrotizing fasciitis

Answer 25

a mixed infection caused by aerobic nd anaerobic bacteria and occurs most commonly after surgical procedures and in patients with diabetes and peripheral vascular disease.

Question 26

type 2 necrotizing fasciitis

Answer 26

monomicrobial infection caued by group A streptococcus (GAS, streptoccus pyogenes). Necrotizing fasciitis caused by community associated methaicillin resistant staphylococcus aureus (MRSA) as a monomicrobial infection has also been described.

Question 27

Necrotizing fasciitis caused by V. vulnificus

Answer 27

rapidly progressive wound infections after exposure to contaminated seawater the wound infections are characterized by initial swelling, erythema, and pain followed by the development of vesicles or bullae and eventual tissue necrosis mortality: 50%

Question 28

Myonecrosis

Answer 28

Most often due to C. perfringens, C. septicum, C. histolyticum or C. Sordellii usually associated with local trauma Gas is always found in the skin, but fascia and deep muscle spared Non clostridial cellulitis is due to infection with a mixed anaerobic and aerobic organisms that produce gas. Associated with diabetes with a foul odor. Myonecrosis is found in 50% of patients with necrotizing fasciitis caused by GAS.

Question 29

Staphylococcal scalded skin syndrome (ritter's disease)

Answer 29

perioral erythema covers entire body within two days psoitive nikolsky's sign: large blisters with clear fluid, no organism, no leucocytes exfoliative toxin destroys the intracellular connections in the skin

Question 30

Pseudomonas aeruginosa

Answer 30

Gram negative aerobic and (anaerobic) rod shaped motile (pili and flagella) grape like odor environmental bacterium simple growth requirement

Question 31

Pseudomonas folliculitis

Answer 31

resulting from immersion in contaminated water such as hot tubs, whirlpools, swimming pools a secondary infection in people who have acne or who depilate their legs fingernail infection

Question 32

Mycobacterium leprae

Answer 32

an obligately aerobic rod with gram + like wall the infections are caused by aerosols can not be grown in vitro two animal models: armadillo and in the footpads of mice grow best in skin histocytes, endothelial cells and the schwann cells of peripheral nerves

Question 33

Lepromatous leprosy

Answer 33

multibacillary. Growth of bactera is relatively unimpeded. Lesions show dense infiltration. Large numbers of bacilli reach bloodstream skin lesions are diffuse, extensive, depiliated, extesnive tissue destruction cell mediated immunty is deficient Th2 response infectivity: high analgous to miliary TB nonreactive to lepromin

Question 34

Treatment of lepromatous leprosy

Answer 34

for epromatous leprosy, the triple therapy with dapsone, ribiospfampin, and clofazimine for a minimum of two years, and maybe lifelong or until biopsies are negatie for acid fast rods for tuberculoid leprosy, a combination of dapsone and rifampin for 6 months is recommended.

Question 35

Tuberculoid leprosy

Answer 35

red blotchy lesions with anesthetic areas. Cell mediated response TH1. Infectivity low.

Question 36

Bacillus anthracis

Answer 36

gram psoitive spore forming capsule (D glutamic acid) exotoxin with three parts: edema factor, lethal factor, protective antigen

Question 37

typical A-B type binary toxin: edema factor and protective antigen + edema toxin

Answer 37

A portion of the edema toxin, adenylate cyclase, similar to the one produced by bordetella pertussis, activated by human calmodulin, resulting in increased intracellular cAMP-impared flow of ions and water

Question 38

typical A-B type binary toxin: lethal factor + protective antigen = lethal toxin

Answer 38

a portion of the letal toxin, a protease induces macrophage to produce high levels of cytokines that trigger the shock

Question 39

protective antigen

Answer 39

B portion of the A-B toxin that promotes entry of EF into phagocytic cells

Question 40

Inhalation ahtrax

Answer 40

by inhalation of aerosolized spores. mediastinal widening replication occurs wtihin the lung with local exotoxin release fever, shortness of breath, cough, HA, vomiting, chills, and chest and abdominal pain. Later progression: respiratory distress and death within 3 days of initial symptoms

Question 41

cutaneous anthrax

Answer 41

most common. Painless papule at the site of incoulation progress to an ulcer surrounding vesicles. necrotic eschar germination, rapid proliferation, taxin release and localized tissue necrosis. Round black lesion with a rim of edema: malignant pustule

Question 42

B. anthracis: Lab diagnosis

Answer 42

microscopic examination of material from papules. No spores in clinical specimen, serpentine chain of bacilli culture: non hemolytic, sticky, colonies biochemical tests ultimately should confirm presumptive diagnosis

Question 43

B anthracis: protection and terapy

Answer 43

inactivated cell free product as vaccine against PA short term. Live attenuated vaccine is also available treatment should last for 60 days with: penicillin, ciprofloxacin, doxycycline