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Block 7 Week 2 > Kozel: Skin and Soft Tissue Infections > Flashcards

Kozel: Skin and Soft Tissue Infections Flashcards

1
Q

Any skin infection that is pyogenic

A

pyoderma

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2
Q

What is primary pyoderma?

A

primary pyoderma is called impetigo; it is a vesicular, later crusted, superficial infection of skin

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3
Q

What two bacteria can cause non-bullous impetigo? Which is the most common?

A

Streptococcus pyogenes

Staph aureus **most common

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4
Q

How does non-bullous impetigo typically present?

A

begins as erythematous papules that evolve into vesicles and pustules and rupture; they dry to form honey-colored crusts on an erythematous base

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5
Q

Does non-bullous impetigo typically scar?

A

no; non-bullous impetigo typically heals without scarring

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6
Q

What bacteria is responsible for bullous impetigo?

A

Staph aureus produces an exfoliating toxin that cleaves the dermal-epidermal junction

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7
Q

This is an ulcerative pyoderma of skin. It is a deeper form of impetigo that follows insect bites or trauma. Caused by Staph aureus or Strep pyogenes. It usually heals with scarring.

A

Ecthyma

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8
Q

So, what is the difference between impetigo and ecthyma?

A

ecthyma is a deeper form of impetigo

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9
Q

What are five purulent manifestations of primary pyoderma?

A 
cutaneous abscess
folliculitis
carbuncles
furuncles
chancriform lesions
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10
Q

This is a collection of pus within the dermis and deeper tissue, usu caused by S. aureus

A

cutaneous abscess

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11
Q

This is pyoderma located within a hair follicle

A

folliculitis

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12
Q

This is an inflammatory nodule extending into subcutaneous tissue, follows folliculitis

A

Furuncle (boil)

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13
Q

This is a coalescent process involving multiple follicles

A

Carbuncle

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14
Q

One manifestation of purulent primary pyoderma is chancriform or ulcerative lesions; list three types of chancriform lesions

A 
cutaneous anthrax (Bacillus anthracis; eschar)
venereal infections (Treponema pallidum - syphilis)
other infections (ex: franscisella tularensis)
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15
Q

These are diffuse, superficial, spreading skin infections

A

cellulitis and erysipelas

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16
Q

Infection involving upper dermis and subcutaneous fat
Follows previous trauma, often minor, or underlying skin lesion, e.g., furuncle or ecthyma
Pain, erythema, involved area very red, hot and swollen

A

Cellulitis

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17
Q

What causes cellulitis? What does cellulitis require?

A

Group A strep and others; less often S. aureus and other bacteria; requires antimicrobial therapy

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18
Q

Superficial cellulitis with prominent lymphatic involvement

Painful; sharp demarcation from adjacent normal skin

A

Erysipelas

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19
Q

What bug causes erysipelas? How does erysipelas differ from cellulitis?

A

almost entirely caused by S. pyogenes; more superficial than cellulitis, involves lymph nodes, and forms sharp demarcation from surrounding normal skin

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20
Q

Aggressive subcutaneous infection that tracks along the superficial fascia – all tissue between skin and underlying muscle
Most often an extension from a skin lesion
Systemic toxicity

A

Necrotizing fasciitis

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21
Q

What bugs can cause necrotizing fasciitis?

A

S. pyogenes
S. aureus
Vibrio vulnificus
Aeromonas

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22
Q

List three examples of systemic bacterial infections that produce rashes or skin lesions

A

Streptobacillus moniliformis: rat-bite fever with petechial/purpuric lesions

Borrelia burgdorfi: erythema migrans

Leptospirosis: macropapular rash

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23
Q

List three toxin-induces skin reactions

A

scarlet fever
scalded skin syndrome
toxic shock syndrome

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24
Q

Follows pharyngitis by group A streptococcus

Streptococcal pyogenic exotoxin A (SpeA)

A

Scarlet fever

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25
Q

Follows local infection by Staphylococcus aureus

Staphylococcal exfoliating toxin

A

Scalded skin syndrome

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26
Q

Follows infection by Staphylococcus aureus

Staphylococcal TSST-1 - superantigen

A

Toxic shock syndrome

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27
Q

List some examples of skin infections following animal contact

A

Cutaneous anthrax (seen in veterinarians)
Cat-scratch disease (Bartonella henselae)
Erysipeloid (contact w fish, marine animals, pigs, poultry)
Pasteurella multocida (dog and cat bites)
Bubonic plague (Yersinia pestis)
Tularemia (Francisella tularensis)

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28
Q

Presence of pus within individual muscle groups
Usually S. aureus (90%)
Most cases in tropics

A

pyomyositis

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29
Q

Necrotic damage to muscle tissue
Occurs after muscle injury and contamination with soil or other material containing spores
Extreme pain, crepitus due to gas formation, yellowish/bronze discoloration
Etiology: Clostridium perfringens (most common) and other clostridial species

A

gas gangrene

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30
Q

What is Group A strep (GAS) a synonym for?

A

Strep pyogenes

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31
Q

Are streptococci:

gram + or gram -
catalase + or catalase -
aerobic or anaerobic

A

gram +; catalase -; facultative anaerobes

**distinguish from staph, because staph is catalase +

32
Q

What are 3 ways to classify streptococci?

A

hemolytic pattern on blood agar (alpha, beta, non-hemolytic)
antigenic (lancefield grouping)
biochemical properties

33
Q

How can you tell alpha from beta from gamma or non-hemolytic on blood agar?

A

alpha - partial hemolysis and greening of agar
beta - complete hemolysis creating a clear zone
gamma - no hemolysis

34
Q

Which hemolytic group- alpha, beta, or gamma- produces streptolysins O and S?

A

beta

35
Q

Which bacterium has group A carbohydrate? Which bacteria has groups B, C, F, G, H, K, L carbohydrate? Which bacteria have groups E, M, N carbohydrate? What about group D?

A

S. pyogenes; normal flora of mucous membranes; bacteria found in lower animals; enterococcus

36
Q 
What is the serological classification for the following:
S. pyogenes?
S. agalactiae?
S. pneumoniae?
S. viridans?
A

S. pyogenes: A antigen, beta hemolytic

S. agalactiae: B antigen, beta hemolytic

S. pneumoniae: no antigen, alpha hemolytic

S. viridans: no antigen, alpha or beta hemolytic

37
Q

What are two antigens that can be found on S. pyogenes? Which antigen induces type-specific protective immunity?

A

Lancefield carbohydrate and M protein

**M protein induces type-specific protective immunity

38
Q

2 extracellular enzymes associated w S. pyogenes?

A

streptolysin O

DNAse

39
Q

What can Group A strep (GAS or S. pyogenes) cause?

A

pharyngitis **most pharyngitis is viral, but this is the most common bacterial cause
skin infections: impetigo, erysipelas, cellulitis, myositis and necrotizing fasciitis
bacteremia
toxemia: scarlet fever and TSS
non-pus forming disease: glomerulonephritis and Rheumatic fever

40
Q

What is unique about erysipelas?

A

it forms a fiery red or salmon colored cellulitis that has well demarcated edges

41
Q

List four virulence factors that S. pyogenes presents with. What is the primary mechanism of virulence by each of these factors?

A

Lipoteichoic acid (in cell wall of gram + bacteria)
F protein
M protein
Hyaluronic acid capsule;
they all promote adherence of the bacteria to nasopharyngeal/epithelial cells

42
Q

This antigen is ESSENTIAL for the virulence of S. pyogenes; it is anti-phagocytic, meaning it keeps the organism outside of phagocytic cells

A

M protein

43
Q

What are two toxins associated with S. pyogenes, and what does each cause?

A
  1. streptococcal pyrogenic exotoxins (Spe): fever/rash of scarlet fever, TSS, due to superantigen release
  2. lipoteichoic acid: inflammation
44
Q

Describe the rash seen in scarlet fever

A

red cheeks, but pale around the nose/mouth; fine, red rough-textured rash like sand-paper

45
Q

This is the only antigen of S. pyogenes that confers long-term type-specific immunity to infection

A

M protein

46
Q

What are two serological assays (antibody tests) that you might do to confirm infection by S. pyogenes?

A

Anti-streptolysin O *useful in diagnosing rheumatic fever

Anti-DNAse *useful if glomerulonephritis is suspected

47
Q

One is one reservoir of S. pyogenes transmission?

A

asymptomatic carriers (carry S. pyogenes in nasopharynx)

48
Q

What is the first choice for treatment of streptococcal infection?

A

penicillin

**prompt use reduces antibody response

49
Q

What is the goal of treatment of streptococcal infections?

A

reduce the level of antigen in the body so that the patient does not have an immune response

50
Q

What are some issues when administering penicillin for a streptococcal infection??

A
  • possible mixed infection
  • necrotizing fasciitis - need high dose penicillin + clindamycin + drainage
  • allergy
51
Q

What does Staph aureus usually look like on blood agar?

A

golden colored colonies

52
Q

Is staph aureus:

gram + or gram -
catalase + or catalase -
alpha, beta, or non-hemolytic

A

gram +; catalase +; beta or non-hemolytic

53
Q

What do Staph aureus bacteria carry?

A

plasmids and bacteriophages which confer antibiotic resistance and toxins

54
Q

If 80% of the S. aureus genome is core genome, what is the remainder of the genome made up of?

A

mobine DNA with plasmids, bacteriophages, and transposons which may code for virulence factors and antibiotic resistance

55
Q

What types of infections does Staph aureus cause?

A

impetigo: bullous and pustular
abscesses, folliculitis, furuncles and carbuncles
deep infections: bacteremia, osteomyelitis and septic arthritis, pneumonia
staph toxins: food poisoning, scalded skin syndrome, TSS

56
Q

What are 3 diseases caused by staphylococcal toxins? Which is the most common?

A
  1. food poisoning **most common cause of food poisoning in the US
  2. scalded skin syndrome
  3. TSS
57
Q

Is staph as virulent as strep?

A

no, it is only weakly virulent

58
Q

Describe the lesions seen in staph infection

A

suppuration (pus)
irreversible tissue damage
scarring

59
Q

What are some of the virulence factors for staphylococci?

A 
antiphagocytic capsule
lipoteichoic acids --> contribute to inflammation
protein A
coagulase
catalase
penicillinase
60
Q

List some of the toxins produced by staph

A

cytotoxins: alpha, beta, delta, gamma, P-V leukocidin
exfoliating toxin: scalded skin syndrome
pyrogenic exotoxins: super-antigens like TSS or staph enterotoxins

61
Q

Staph food poisoning is the number 1 cause of food poisoning in the US. It is due to the ingestion of (blank)

A

preformed staphylococcal enterotoxin

**in this form of poisoning, you ingest the toxin, not the organism that makes the toxin

62
Q

What does staph food poisoning cause?

A

well, it targets the sensory smooth nerve endings in smooth muscle of the intestine causing nausea, cramps, vomiting, and diarrhea

63
Q

Describe scalded skin syndrome caused by staph

A

It is an exfoliative skin disease; so, there is an infection w staph at a distant site, but the release of this exfoliating toxin (a serine protease) cleaves the dermal-epidermal junction and forms fragile thin-roofed vesicopustules

64
Q

What is the local form of scalded skin syndrome called?

A

bullous impetigo

65
Q

What are the symptoms of toxic shock syndrome caused by staph?

A 
fever
vomiting
diarrhea
rash
shock
66
Q

T/F: Superantigens can activate ~10% of your T cells all at once

A

True

67
Q

These two bacterial exotoxins both cause fever and systemic effects and act as superantigens causing massive cytokine release and T cell activation

A

SpeA (strep pyrogenic exotoxin)

TSST-1

68
Q

This test distinguishes Staph aureus from other staphylococci

A

coagulase test

69
Q

Two ways to recognize MRSA?

A

chromogenic media with disks (like we did in lab)

PCR for mecA (which carries resistance to methicillin)

70
Q

What is the primary reservoir for staph?

A

man

**staph makes up the normal flora of the large bowel, the skin, the anterior nares

71
Q

How is staph infection acquired?

A

from air, direct contact, or endogenously

**high rate in hospitals which may require screening for nasal carriers and decontamination

72
Q

Treatment of staph?

A

drain the lesion!!
control the underlying disease
antibiotics (like penicillinase-resistant penicillins, clindamycin, TMP-SMX)

73
Q

What is the mechanism of resistance for VISA (vancomycin intermediate S. aureus)?

A

cell wall with free ala-ala groups; acts as a decoy for vancomycin

74
Q

What is the mechanism of resitance for VRSA (vancomycin resistant S. aureus)?

A

ala-lactate production; acts as decoy for vancomycin

75
Q

What does the mecA gene code for in MRSA?

A

an altered penicillin binding site with low affinity for beta-lactam antibiotics

76
Q

This type of MRSA is associated with risk factors, i.e. surgery, indwelling catheter, etc

A

Health care-associated MRSA

77
Q

This type of MRSA has no/limited risk factors. It is the most common cause of skin and soft tissue infections in community
Usually carries the PV leukocidin
Pauci-resistant

A

community-associated MRSA

Block 7 Week 2 (9 decks)

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