Pyogenic Flashcards
What are the major pathogens involved in infections of the skin and underlying tissues?
Staphylococcus aureus and Streptococcus pyogenes
Both can cause bloodstream infection (sepsis)
What is the typical Gram stain appearance of Staphylococcus aureus?
Clusters
S. aureus appears as clusters in a Gram stain
What is the typical Gram stain appearance of Streptococcus pyogenes?
Chains
S. pyogenes appears as chains in a Gram stain
What are some common infections caused by Staphylococcus aureus?
- 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)
What are the distinguishing features of S. aureus?
- Catalase positive
- Coagulase positive
- Penicillin resistance
- Tendency to cause localized infections (abscesses)
S. aureus shows high antimicrobial resistance
What are the distinguishing features of S. pyogenes?
- Catalase negative
- Coagulase negative
- Penicillin susceptible
- Tendency to produce spreading infections
S. pyogenes is less resistant to antimicrobials compared to S. aureus
What are some virulence factors of Staphylococcus aureus?
- Protein A
- Capsule
- Biofilms
- Secreted enzymes (invasins)
- Toxins (e.g., PVL, α-toxin)
These factors contribute to immune evasion and tissue damage
What are some virulence factors of Streptococcus pyogenes?
- 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
What are some common skin and soft tissue infections caused by Staphylococcus aureus and Streptococcus pyogenes?
- Impetigo
- Folliculitis
- Furuncles
- Carbuncles
- Cellulitis
- Erysipelas
- Necrotizing fasciitis
These infections are prevalent in New Zealand
What is the treatment for minor skin infections caused by S. aureus?
Topical antiseptics and antimicrobials
Oral or IV antibiotics may be required if the infection progresses
What is the treatment for infections caused by methicillin-resistant Staphylococcus aureus (MRSA)?
Vancomycin
MRSA is resistant to flucloxacillin and other beta-lactams
What is folliculitis?
Infection of hair follicles leading to small papules that evolve into pustules
Typically caused by S. aureus
What characterizes a furuncle?
A deeper infection of a hair follicle with pus, arising from folliculitis
S. aureus is commonly the causative agent
What distinguishes a carbuncle from a furuncle?
Extensive infection of hair follicles, usually causing systemic symptoms like fever
Carbuncles typically occur on the neck, back, or thighs
What are the symptoms of cellulitis?
- Pain
- Heat
- Swelling
- Erythema
- Fever
- Chills
- Nausea
- Leukocytosis
Complications can include abscess and sepsis
True or False: Streptococcus pyogenes is resistant to penicillin.
False
S. pyogenes remains susceptible to penicillin
Fill in the blank: The _______ protein in S. pyogenes plays an important role in rheumatic fever.
M
Antibodies against M protein can cross-react with self-tissues
What is the percentage of bacteraemia cases associated with pyodermas?
30%
Bacteraemia refers to the presence of bacteria in the bloodstream.
List some complications of pyodermas.
- Abscess
- Osteomyelitis
- Septic arthritis
- Sepsis
- Necrotizing fasciitis
What are the most common aetiological agents of pyodermas?
- S. aureus
- S. pyogenes
- Other Gram +ve cocci (enterococci, staphs, streps)
- Gram –ve rods
- Anaerobes
What are some risk factors for cellulitis?
- Trauma
- Diabetes
- Vascular disease
- Pregnancy
- Obesity
- Immune deficiency
- Age
How is cellulitis diagnosed?
- Clinical diagnosis
- Culture of aspirates, abscesses, pustules, wounds
- Blood cultures if febrile
What is erysipelas?
Superficial cellulitis with lymphatic involvement caused by S. pyogenes
Symptoms include a bright red, well-demarcated lesion.
What are some symptoms of erysipelas?
- Bright red, well-demarcated lesion
- Systemic symptoms (fever, chills, malaise, leukocytosis)
- Typically affects legs/face
What is necrotizing fasciitis?
A rapid, spreading, destructive infection along fascia with high mortality
Mortality exceeds 90% if treatment is delayed.
What are common pathogens involved in necrotizing fasciitis?
- S. pyogenes
- S. aureus
- Often polymicrobial with aerobic/anaerobes
What are the diagnostic criteria for necrotizing fasciitis?
- Clinical signs (edematous, erythematous, intensely painful)
- Rapidly advancing cellulitis
- Laboratory culture & antimicrobial sensitivities
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
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
What is the resistance profile of S. aureus?
Over 50% are penicillin resistant
MRSA (Methicillin-resistant Staphylococcus aureus) is resistant to flucloxacillin.
What are some important Staphylococcus species associated with infections?
- S. epidermidis (HAI, device-associated biofilm infections)
- S. saprophyticus (UTI in young women)
What is the role of M protein in S. pyogenes?
- Antigenic variation
- Repels phagocytes
- Inhibits opsonisation
- Binds fibronectin
What types of infections can S. pyogenes cause?
- Pharyngitis
- Skin infections
- Pneumonia
- Endocarditis
- Postpartum infections
- Sepsis
What is the clinical presentation of impetigo?
Thin-walled vesicle on erythematous base that dries to form ‘honey’ colored crusts
Non-bullous impetigo is caused by S. aureus and/or S. pyogenes.
What is folliculitis?
Infection of hair follicles characterized by small papules evolving into pustules
Commonly caused by S. aureus.
What is the significance of the microbiome in skin infections?
Some commensals may be opportunistic pathogens
Microbial virulence, site of infection, and host response influence disease severity.
What are pyodermas?
Skin infections including impetigo, folliculitis, furuncles, and carbuncles
They are often caused by staphs and streps.
Fill in the blank: The most common gram-positive cocci clinically are _______.
Staphylococcus & Streptococcus
True or False: S. aureus is catalase negative.
False
S. aureus is catalase positive.
True or False: S. pyogenes is often associated with localized infections.
False
S. pyogenes is often associated with spreading infections.
What are bullous crusts associated with?
S. aureus and epidermolytic exotoxin
They form fluid-filled vesicles (bullae) and can affect all ages.
How is a diagnosis of bullous lesions made?
Based on clinical presentation and culture of bullous/serous fluid
This can aid in the choice of antimicrobial treatment.
What is folliculitis?
Infection of hair follicles characterized by small papules evolving into pustules
It is typically superficial and often caused by S. aureus.
What are common treatments for folliculitis?
- Topical antiseptics
- Wound care
- Oral antimicrobials if extensive disease
Self-limiting in many cases.
What is a furuncle?
A deeper infection of a hair follicle with pus, also known as a boil
It arises from folliculitis and may present with local cellulitis.
What are the complications associated with a furuncle?
- Abscesses
- Cellulitis
Risk factors include diabetes, obesity, and immunosuppression.
What characterizes a carbuncle?
Extensive infection of hair follicles, usually located on the neck, back, or thighs
It is often associated with systemic symptoms such as fever and nausea.
What are the common symptoms of cellulitis?
- Pain
- Heat
- Swelling
- Erythema
- Fever
- Chills
- Nausea
- Leukocytosis
Complications can include abscess, osteomyelitis, and sepsis.
What are the most common aetiological agents of cellulitis?
- S. aureus
- S. pyogenes
- Other Gram-positive cocci
- Gram-negative rods
- Anaerobes
Cellulitis may also be polymicrobial.
What are risk factors for developing cellulitis?
- Trauma
- Diabetes
- Vascular disease
- Pregnancy
- Obesity
- Immune deficiency
- Age
These factors increase susceptibility to infection.
What is erysipelas?
A superficial cellulitis with lymphatic involvement, primarily caused by S. pyogenes
Symptoms include a bright red, well-demarcated lesion.
What are the complications of erysipelas?
- Sepsis
- Septic arthritis
- Infective endocarditis
- Lymphatic damage
- Necrotizing fasciitis
It is typically more severe in those with risk factors.
What is necrotizing fasciitis?
A rapid, spreading, destructive infection along the fascia
It has a high mortality rate, especially if treatment is delayed.
What are the common causative organisms of necrotizing fasciitis?
- S. pyogenes
- S. aureus
- Most infections are polymicrobial
They often include aerobic and anaerobic bacteria.
What symptoms are associated with necrotizing fasciitis?
- Oedema
- Erythema
- Intense pain
- Warmth
- Tenderness
- Fever
- Malaise
Rapidly advancing cellulitis is also characteristic.
What is the initial treatment for skin and soft tissue infections?
- Wound care
- Topical antiseptics for minor infections
- Surgical drainage for abscesses
Oral or IV antimicrobials may be required if there is a risk of progression.
What is a common antimicrobial treatment for S. aureus infections?
Flucloxacillin
Over 50% of S. aureus strains are resistant to penicillin.
What is the treatment for MRSA infections?
Vancomycin
MRSA is resistant to flucloxacillin.
What are the common causes of skin infections?
- S. aureus for localized infections (abscesses)
- S. pyogenes for spreading infections
Rates of skin infections are notably high in certain populations.
What is the significance of Gram-positive cocci in clinical samples?
- Staphs appear in clusters (catalase +ve)
- Streps appear in pairs/chains (catalase -ve)
They are part of the microbiome and can indicate infection.
