Gram +ve Bacteria Flashcards
(16 cards)
What are the similarities & differences in gram +ve and -ve bacteria
- BOTH have plasma membrane
- BOTH have peptidoglycan layer
•
What bacteria is mostly (90%) the cause of osteomyelitis
• Staphylococcus aureus;
(Habitat mostly nose & skin)
Treatment:
- flucloxacillin 3 months
What is Coagulase
An enzyme produced by bacteria that clots blood plasma. Fibrin clot formation around bacteria may protect from phagocytosis
Staph. aureus (coagulase positive +ve)
• Spread by aerosol & touch
- can have either carriers or shedders
• MRSA -
RESISTANT FACTORS:
- Beta-lactams
- gentamicin, erythromycin, tetracycline
What are the Virulence factors of Staph. aureus
• Pore-forming toxins (some strains)
- alpha-haemolysin & Panton-Valentine Leucocidin (PVL toxin causes haemorrhagic pneumonia)
• Proteases:
- Exfoliatin - scalded skin syndrome
• Toxic Shock Syndrome toxin (TSST) - stimulates cytokine release
• Protein A:
- surface protein which binds Ig’s in wrong orientation preventing opsonisation & phagocytosis
Coagulase negative Staphylococci
• S.epidermidis
- OPPORTUNISTIC infections in debilitated, prostheses, catheters
- Main virulence factor is its ability to form persistent biofilms
• S.saprophyticus
- Causes Acute Cystitis:
- Releases haemagglutinin for adhesion to human cells
- Releases Urease - kidney stones
Wound received to shoulder. Spreading inflammation leading to fever and malaise. What bacteria?
• Swab culture:
STREPTOCOCCUS PYOGENES:
Presents as “chains”
Staphylococci presents as clusters
- beta-haemolytic, (group A)
- Facultatively anaerobic
- Penicillin sensitive
What is Haemolysis
Haemolysis is the destruction of red blood cells
• ALPHA:
- partial haemolysis
- e.g.) S.intermedius
- H2o2 reacts with Haemoglobin
- green colour
• BETA:
- complete lysis
e. g.) S.pyogenes - release haemolysins O & S
• Non (or GAMMA) - NO LYSIS
e.g) Some S.mutans
In what three ways can Streptococci be classified
1.) Haemolysis
2.) Lancefield typing
(based on carbohyrate cell surface antigens on catalase -ve, coagulase -ve bacteria)
3.) Biochemical properties
What are the infections caused by S.pyogenes
- Wound infections - cellulitis
- Tonsillitis & Pharyngitis
- Otitis media (inner ear)
- Impetigo
- Scarlet fever
Complications of S.pyogenes infections
prompt treated is needed to S.pyogenes that give rise to immunologically mediated complications
• Rheumatic fever
- inflammatory disease of the heart, joints.
It often follows a Strep. throat infection
• Glomerulonephritis:
- inflammatory disease sometimes following S.pyogenes infection
Can assess risk by doing an Anti-SLO titre
What are the virulence factors of S. progenies
• CAPSULE:
- made of hyaluronic acid which protects from phagocytosis
• M PROTEIN (surface protein):
- Encourages complement degradation
EXPORTED FACTORS;
• ENZYMES:
- Streptokinase (breaks down clots)
- C5a peptidase - reduces chemotaxis
• TOXINS:
- Streptolysins O&S - binds cholestrol
- Erythrogenic toxin - SPeA which causes exaggerated response in host
S.pneumoniae
Presents as ‘Draughtsman colonies’
CAUSES:
- pneumonia
- otitis media
- sinusitis
- meningitis
PREDISPOSING FACTORS
- impaired mucus trapping (e.g. viral infection)
- hypogammaglobulinaemia
- asplenia
S.pneumoniae virulence factors
• CAPSULE:
- polysaccharide (84 types), antiphagocytic
• INFLAMMATORY WALL CONSTITUENTS:
- teichoic acid (choline)
- peptidoglycan
• CYTOTOXIN:
- pneumolysin
What is the collective name for oral streptococci
VIRIDANS STREPTOCOCCI
- alpha or non-haemolytic
- some cause dental caries & abscesses
• important in infective endocarditis
- S. sanguinis, S.oralis
- Can cause deep organ abscesses (e.g. brain. liver)
- Most virulent are the ‘milleri group’
- S.intermedius
- S. anginosus
- S. constellatus
C. diptheriae
• Droplet spread
• Can grow in the presence of potassium tellurite:
- selective method for isolating this bacteria from the throat
• Toxin:
- Inhibits protein synthesis (inactivates elongation factor-2 in host cells by adding ADP-ribosyl group to aa dipthamide)
Prevention:
Vaccination - toxoid
(Inactivated toxin)
