lecture 3 - pyogenic gram-positive cocci Flashcards
What is the full name of staph. a?
Staphylococcus aureus
What is the full name of strep p.?
Streptococcus pyogenes
What are the 2 bacteria that most commonly cause skin and soft tissue infections?
Staphylococcus aureus & streptococcus pyogenes
What classfication of bacteria are staph. aureus and strep. pyogenes?
pyogenic, gram-positive cocci
What does pyogenic mean?
Pus producing - purulent
What are the components of pus?
bacteria, neutrophils, fibrin
What is the inflammatory exudate in pyogenic gram-positive cocci infections?
Pus
What is an abscess?
Localised collection of pus in a fibrin-lined cavity
What is the arrangement of staph. aureus?
clusters
What is the arrangement of strep. pyogenes?
chains
Are strep and staph aerobic or anaerobic?
Facultative anaerobic - can grow either aerobically or anaerobically.
What does facultative anaerobic mean?
A bacteria than can grow aerobically or anaerobically.
Are staph. aureus infections typically localised or spreading?
localised - abscesses
Are strep. pyogenes infections typically localised or spreading?
spreading
Is staph. aureus or strep. pyogenes more antimicrobial resistant?
Staph. aureus
Is staph. aureus catalase negative or positive?
catalase positive
Is strep. pyogenes catalase negative or positive?
catalase negative
What does it mean if a bacteria is catalase positive?
It has the catalase enzyme, which converts H2O2 to O2
What bacteria is the most common cause of skin and wound infections, and abscesses?
Staph. aureus
Where is staph. aureus typically carried non-infectiously?
The nose
What toxin does staph. aeureus have to kill neutrophils?
PVL - panton valentine leukocidin.
What is bacterial coagulase?
A protein that sits on the surface of bacteria that converts fibrinogen to fibrin.
What is the function of bound bacterial coagulase?
Bound to the cell wall and converts fibrinogen to fibrin, causing clotting of the blood.
What protein/enzyme does S. aureus have that results in blood plasma clotting?
Coagulase
What are the infections commonly caused by strep. pyogenes?
Pharyngitis, skin infections, pneumonia, endocarditis, sepsis, rheumatic fever (from Group A streps)
What are the post-infectious conditions caused by strep. pyogenes?
Rheumatic fever, acute glomerulonephritis
Where is strep. pyogenes typically carried?
The pharynx/throat
What is the most important virulence factor of strep. pyogenes?
M protein
What feature of strep. pyogenes allows it to repel phagocytes?
M protein in the bacterial cell wall provides a negative charge which repels negatively charge phagocytes.
What are pyodermas?
purulent bacterial skin infections
What are the 4 types of pyodermas in order of increasing severity?
Impetigo, folliculitis, furuncles, carbuncles
What is the common name for impetigo?
school sores
What are the 2 forms of impetigo?
Non-bullous & bullous
What bacteria causes non-bullous impetigo?
Staph. aureus &/or strep. pyogenes
What age group is most likely to develop non-bullous impetigo?
Children
How does non-bullous impetigo present?
Red sores around the mouth and nose that dry to form golden coloured crusts.
What bacteria causes bullous impetigo?
Staph. aureus
What is the presentation of bullous impetigo?
Fluid filled vesicles (bullae) on the skin anywhere in the body
What is the age group most affected by bullous impetigo?
All ages are affected.
What is folliculitis?
Infection of hair follicles
What is the presentation of folliculitis?
Small papules around hair follicles that evolve into pustules.
What is the difference between papules & pustules in folliculitis?
Papules are hard, raised red lumps around follicles that evolve into pustules - small superficial abscesses.
What are the treatments for folliculitis?
Topical antimicrobials, followed by oral antimicrobials in serious or extensive cases.
What is the common name for furuncles?
Boils
What condition progresses into the formation of a furuncle?
Folliculitis
What is a furuncle?
Deeper infection of a hair follicle with pus, and local cellulitis surrounding the follicle.
What bacteria typically causes a furuncle?
Staph. aureus
What are the risk factors for developing a furuncle?
Diabetes, obesity, carriage of stap. aureus, immunosuppression
What are carbuncles?
Extensive infection of a group of follicles
Where are carbuncles typically found?
The neck, back, thighs
What bacteria typically causes carbuncles?
Staph. aureus
What is cellulitis?
Acute spreading of skin infection involving the dermis & hypodermis
What are the symptoms of cellulitis?
Little necrosis, oedema/swelling, ill-defined margins of red skin merging smoothly with adjacent skin, pain, heat, tenderness, fever, etc.
What are the complications of cellulitis?
Abscess, osteomyelitis, sepsis, necrotising fasciitis
What bacteria most commonly cause cellultis?
gram-positive cocci - staph. aureus & strep. pyogenes
What are the risk factors for cellulitis?
trauma, diabetes, obesity, age, immunosupression, vascular disease, pregnancy
What is erysipelas?
Superficial cellulitis with lymphatic involvement.
What are the symptoms of erysipelas?
bright red, well demarcated, hard, swollen lesion. accompanied by systemic symptoms such as fever, chills, malaise
What is necrotizing fasciitis?
Rapid, spreading, destructive infection along the fascia
What is fascia?
Fibrous connective tissue between the skin and muscle
Why does necrotizing fasciitis have a high mortality?
It cause sepsis, which leads to multi-organ failure.
What bacteria commonly cause necrotizing fasciitis?
usually polymicrobial - often staph. aureus & strep. pyogenes
What are the typical treatments for pyodermas?
antimicrobials avoided unless advanced, topical antiseptics
What are the typical treatments for carbuncles?
surgical drainage, antimicrobials
How are advanced skin infection such as necrotising fasciitis and cellulitis initially treated?
Empiric therapy
What is empiric therapy in terms of antimicrobial drugs?
The early delivery of broad spectrum antimicrobial drugs, despite not yet having a diagnosis of the bacteria present, to help prevent rapid spread in acute infections.
What is the most commonly used antibiotic for Staph. aureus infections, and why?
Flucloxacillin, many strains are resistant to penicillin.
What is the antimicrobial used to treat MRSA (methicillin resistant stapholococcus aureus) infections?
Vancomycin
What is the antimicrobial most commonly used to treat strep. pyogenes infections?
penicillin
