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MICN201 2025 Infection & Immunity > Pyogenic > Flashcards

Pyogenic Flashcards

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1
Q

What are the major pathogens involved in infections of the skin and underlying tissues?

A

Staphylococcus aureus and Streptococcus pyogenes

Both can cause bloodstream infection (sepsis)

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2
Q

What is the typical Gram stain appearance of Staphylococcus aureus?

A

Clusters

S. aureus appears as clusters in a Gram stain

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3
Q

What is the typical Gram stain appearance of Streptococcus pyogenes?

A

Chains

S. pyogenes appears as chains in a Gram stain

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4
Q

What are some common infections caused by Staphylococcus aureus?

A
  • Skin infections
  • Wound infections
  • Abscesses
  • Osteomyelitis
  • Septic arthritis
  • Food poisoning
  • Eye infections
  • Pneumonia
  • Endocarditis
  • Meningitis
  • Sepsis

S. aureus is a major cause of healthcare-associated infections (HAI)

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5
Q

What are the distinguishing features of S. aureus?

A
  • Catalase positive
  • Coagulase positive
  • Penicillin resistance
  • Tendency to cause localized infections (abscesses)

S. aureus shows high antimicrobial resistance

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6
Q

What are the distinguishing features of S. pyogenes?

A
  • Catalase negative
  • Coagulase negative
  • Penicillin susceptible
  • Tendency to produce spreading infections

S. pyogenes is less resistant to antimicrobials compared to S. aureus

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7
Q

What are some virulence factors of Staphylococcus aureus?

A
  • Protein A
  • Capsule
  • Biofilms
  • Secreted enzymes (invasins)
  • Toxins (e.g., PVL, α-toxin)

These factors contribute to immune evasion and tissue damage

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8
Q

What are some virulence factors of Streptococcus pyogenes?

A
  • M protein
  • Capsule (hyaluronic acid)
  • Protein G
  • Biofilms
  • Enzymes (e.g., C5a peptidase, DNase)
  • Toxins (e.g., erythrogenic toxins)

M protein plays a significant role in rheumatic fever

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9
Q

What are some common skin and soft tissue infections caused by Staphylococcus aureus and Streptococcus pyogenes?

A
  • Impetigo
  • Folliculitis
  • Furuncles
  • Carbuncles
  • Cellulitis
  • Erysipelas
  • Necrotizing fasciitis

These infections are prevalent in New Zealand

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10
Q

What is the treatment for minor skin infections caused by S. aureus?

A

Topical antiseptics and antimicrobials

Oral or IV antibiotics may be required if the infection progresses

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11
Q

What is the treatment for infections caused by methicillin-resistant Staphylococcus aureus (MRSA)?

A

Vancomycin

MRSA is resistant to flucloxacillin and other beta-lactams

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12
Q

What is folliculitis?

A

Infection of hair follicles leading to small papules that evolve into pustules

Typically caused by S. aureus

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13
Q

What characterizes a furuncle?

A

A deeper infection of a hair follicle with pus, arising from folliculitis

S. aureus is commonly the causative agent

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14
Q

What distinguishes a carbuncle from a furuncle?

A

Extensive infection of hair follicles, usually causing systemic symptoms like fever

Carbuncles typically occur on the neck, back, or thighs

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15
Q

What are the symptoms of cellulitis?

A
  • Pain
  • Heat
  • Swelling
  • Erythema
  • Fever
  • Chills
  • Nausea
  • Leukocytosis

Complications can include abscess and sepsis

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16
Q

True or False: Streptococcus pyogenes is resistant to penicillin.

A

False

S. pyogenes remains susceptible to penicillin

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17
Q

Fill in the blank: The _______ protein in S. pyogenes plays an important role in rheumatic fever.

A

M

Antibodies against M protein can cross-react with self-tissues

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18
Q

What is the percentage of bacteraemia cases associated with pyodermas?

A

30%

Bacteraemia refers to the presence of bacteria in the bloodstream.

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19
Q

List some complications of pyodermas.

A
  • Abscess
  • Osteomyelitis
  • Septic arthritis
  • Sepsis
  • Necrotizing fasciitis
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20
Q

What are the most common aetiological agents of pyodermas?

A
  • S. aureus
  • S. pyogenes
  • Other Gram +ve cocci (enterococci, staphs, streps)
  • Gram –ve rods
  • Anaerobes
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21
Q

What are some risk factors for cellulitis?

A
  • Trauma
  • Diabetes
  • Vascular disease
  • Pregnancy
  • Obesity
  • Immune deficiency
  • Age
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22
Q

How is cellulitis diagnosed?

A
  • Clinical diagnosis
  • Culture of aspirates, abscesses, pustules, wounds
  • Blood cultures if febrile
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23
Q

What is erysipelas?

A

Superficial cellulitis with lymphatic involvement caused by S. pyogenes

Symptoms include a bright red, well-demarcated lesion.

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24
Q

What are some symptoms of erysipelas?

A
  • Bright red, well-demarcated lesion
  • Systemic symptoms (fever, chills, malaise, leukocytosis)
  • Typically affects legs/face
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25
What is necrotizing fasciitis?
A rapid, spreading, destructive infection along fascia with high mortality ## Footnote Mortality exceeds 90% if treatment is delayed.
26
What are common pathogens involved in necrotizing fasciitis?
* S. pyogenes * S. aureus * Often polymicrobial with aerobic/anaerobes
27
What are the diagnostic criteria for necrotizing fasciitis?
* Clinical signs (edematous, erythematous, intensely painful) * Rapidly advancing cellulitis * Laboratory culture & antimicrobial sensitivities
28
What is the treatment for skin and soft tissue infections?
* Minor infections: wound care & topical antiseptics * Abscesses: surgical drainage +/- antimicrobials * Cellulitis: oral/IV antimicrobials * Necrotizing fasciitis: IV antimicrobials + surgical debridement
29
What are the common causes of skin infections in relation to S. aureus and S. pyogenes?
* S. aureus: localized infections (abscesses) * S. pyogenes: spreading infections
30
What is the resistance profile of S. aureus?
Over 50% are penicillin resistant ## Footnote MRSA (Methicillin-resistant Staphylococcus aureus) is resistant to flucloxacillin.
31
What are some important Staphylococcus species associated with infections?
* S. epidermidis (HAI, device-associated biofilm infections) * S. saprophyticus (UTI in young women)
32
What is the role of M protein in S. pyogenes?
* Antigenic variation * Repels phagocytes * Inhibits opsonisation * Binds fibronectin
33
What types of infections can S. pyogenes cause?
* Pharyngitis * Skin infections * Pneumonia * Endocarditis * Postpartum infections * Sepsis
34
What is the clinical presentation of impetigo?
Thin-walled vesicle on erythematous base that dries to form 'honey' colored crusts ## Footnote Non-bullous impetigo is caused by S. aureus and/or S. pyogenes.
35
What is folliculitis?
Infection of hair follicles characterized by small papules evolving into pustules ## Footnote Commonly caused by S. aureus.
36
What is the significance of the microbiome in skin infections?
Some commensals may be opportunistic pathogens ## Footnote Microbial virulence, site of infection, and host response influence disease severity.
37
What are pyodermas?
Skin infections including impetigo, folliculitis, furuncles, and carbuncles ## Footnote They are often caused by staphs and streps.
38
Fill in the blank: The most common gram-positive cocci clinically are _______.
Staphylococcus & Streptococcus
39
True or False: S. aureus is catalase negative.
False ## Footnote S. aureus is catalase positive.
40
True or False: S. pyogenes is often associated with localized infections.
False ## Footnote S. pyogenes is often associated with spreading infections.
41
What are bullous crusts associated with?
S. aureus and epidermolytic exotoxin ## Footnote They form fluid-filled vesicles (bullae) and can affect all ages.
42
How is a diagnosis of bullous lesions made?
Based on clinical presentation and culture of bullous/serous fluid ## Footnote This can aid in the choice of antimicrobial treatment.
43
What is folliculitis?
Infection of hair follicles characterized by small papules evolving into pustules ## Footnote It is typically superficial and often caused by S. aureus.
44
What are common treatments for folliculitis?
* Topical antiseptics * Wound care * Oral antimicrobials if extensive disease ## Footnote Self-limiting in many cases.
45
What is a furuncle?
A deeper infection of a hair follicle with pus, also known as a boil ## Footnote It arises from folliculitis and may present with local cellulitis.
46
What are the complications associated with a furuncle?
* Abscesses * Cellulitis ## Footnote Risk factors include diabetes, obesity, and immunosuppression.
47
What characterizes a carbuncle?
Extensive infection of hair follicles, usually located on the neck, back, or thighs ## Footnote It is often associated with systemic symptoms such as fever and nausea.
48
What are the common symptoms of cellulitis?
* Pain * Heat * Swelling * Erythema * Fever * Chills * Nausea * Leukocytosis ## Footnote Complications can include abscess, osteomyelitis, and sepsis.
49
What are the most common aetiological agents of cellulitis?
* S. aureus * S. pyogenes * Other Gram-positive cocci * Gram-negative rods * Anaerobes ## Footnote Cellulitis may also be polymicrobial.
50
What are risk factors for developing cellulitis?
* Trauma * Diabetes * Vascular disease * Pregnancy * Obesity * Immune deficiency * Age ## Footnote These factors increase susceptibility to infection.
51
What is erysipelas?
A superficial cellulitis with lymphatic involvement, primarily caused by S. pyogenes ## Footnote Symptoms include a bright red, well-demarcated lesion.
52
What are the complications of erysipelas?
* Sepsis * Septic arthritis * Infective endocarditis * Lymphatic damage * Necrotizing fasciitis ## Footnote It is typically more severe in those with risk factors.
53
What is necrotizing fasciitis?
A rapid, spreading, destructive infection along the fascia ## Footnote It has a high mortality rate, especially if treatment is delayed.
54
What are the common causative organisms of necrotizing fasciitis?
* S. pyogenes * S. aureus * Most infections are polymicrobial ## Footnote They often include aerobic and anaerobic bacteria.
55
What symptoms are associated with necrotizing fasciitis?
* Oedema * Erythema * Intense pain * Warmth * Tenderness * Fever * Malaise ## Footnote Rapidly advancing cellulitis is also characteristic.
56
What is the initial treatment for skin and soft tissue infections?
* Wound care * Topical antiseptics for minor infections * Surgical drainage for abscesses ## Footnote Oral or IV antimicrobials may be required if there is a risk of progression.
57
What is a common antimicrobial treatment for S. aureus infections?
Flucloxacillin ## Footnote Over 50% of S. aureus strains are resistant to penicillin.
58
What is the treatment for MRSA infections?
Vancomycin ## Footnote MRSA is resistant to flucloxacillin.
59
What are the common causes of skin infections?
* S. aureus for localized infections (abscesses) * S. pyogenes for spreading infections ## Footnote Rates of skin infections are notably high in certain populations.
60
What is the significance of Gram-positive cocci in clinical samples?
* Staphs appear in clusters (catalase +ve) * Streps appear in pairs/chains (catalase -ve) ## Footnote They are part of the microbiome and can indicate infection.

MICN201 2025 Infection & Immunity (7 decks)

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