Major Gram-Positive Bacterial Pathogens Flashcards
How do they differ from gram -ve bacteria
Lack a periplasmic space
Infection example 1 - OSTEOMYELITIS
caused by?
method of coagulase testing
Virulence factors and effects
- staphylococcus
- 40 species
- can be coagulase +ve or -ve
- incubate bacteria at 37 degrees, -ve will stay liquid +ve clots plasma - may protect from phagocytosis - staph AUREUS
- spread by aerosol and touch
- MRSA - resistant to beta lactams, gentamicin, erythromycin and tetracycline
- pore-forming toxins
- proteases
- exfoliatin –> SKIN SLOUGHING
- toxic shock syndrome toxin –> stimulates cytokine release
- Protein A - surface protein which binds antibodies the wrong way - preventing opsonisation
Associated conditions of S. aureus - pyogenic
Wound infections Abscesses, boils Impetigo Septicaemia Osteomyelitis Pneumonia Endocarditis
Associated conditions of S. aureus - toxin mediated
Scalded skin syndrome
Toxic shock syndrome
Food poisoning
Associated conditions of S. aureus - coagulase positive
Infected implants
Endocarditis
Septicaemia
Coagulase -ve staphylococci examples
Found in
Virulence factors
S. epidermis
- infections in prostheses and catheters
- forms persistent biofilms
S. saprophyticus
- acute cystitis
- haemagglutinin for adhesion
- urease in kidney stones
Infection case 2 - shoulder wound
Progression
Swab culture
Examples of differently lysing
3 days spreading inflammation –> fever and malaise
Streptococcus pyogenes
β-haemolytic - complete lysis of blood e.g s. pyogenes
α - partial haemolysis e.g s. intermedius
ɣ - non haemolytic e.g s mutans
FACULTATIVE ANAEROBE
Penicillin sensitive
Effect of differently haemolysing organisms on horse blood dish
α - partial greening
β - complete lysis
ɣ - no lysis
3 classifications of streptococci
- Haemolytic
- Lancefield grouping
- Biochemical properties
Sero-Grouping
Method of grouping by bacterial carbohydrate cell surface antigens
Lancefield groups
How is group determined
Some more important
A-H and K-V
Antiserum added to each group and then added to a suspension of bacteria
Clumping –> recognition
Group A - S.pyogenes; important pathogen –
Group B - S.agalactiae neonatal infections
Infections caused by S. pyogenes
Wound infections Tonsilitis Otitis media Impetigo Scarlet fever
Complications of S. pyogenes infection
How can risk be investigated??
Rheumatic fever
• Inflammatory disease of heart, joints, skin, brain. Often
follows Strep. throat infection • Antibody cross reactivity
Glomerulonephritis
• Inflammatory disease sometimes following
Anti-SLO titre
Anti-SLO titre
What does SLO result in
What indicated ASLO presence
Anti-streptiolysin O (ASLO) titre – ASLO – Antibody against SLO
Streptolysin O – beta haemolysis of cells
ASLO positive is black dots
• Streptococcal exoenzymes are bound to biologically inert latex particles
• If streptococcal antibodies present in the test sample, reaction occurs.
• presence of an ASO titer of >200 IU/mL in the serum = agglutination of the latex particles.
S. pyogenes virulence factors
Exported
Surface factors
Toxins
Enzymes
Hyaluronidase - spreading
Streptokinase - breaks down clots
C5a peptidase - reduces chemotaxis
Capsule - hyaluronic acid (protection)
M protein – surface protein (encourages complement
degradation) cross reactivity?
Streptolysins O&S - binds cholesterol
Erythrogenic toxin - SPeA – exaggerated response
