Flashcards in L4 - Gram Positive Cocci Deck (23)
What is the mechanism of action of the B-Lactam antibiotics?
They interfere with cell-wall synthesis through a bacterial enzyme called transpeptidase.
Describe the mechanism of resistance of MRSA strains of Staphylococcus aureus to the isoxazolyl penicillins.
They have acquired a gene called mecA which encodes for a transpeptidase, PBP2a.
Name 3 non-suppurative complications of Streptococcus pyogenes infection.
Scarlet fever, Rheumatic fever and acute post-streptococcal glomerulonephritis.
Why do non-suppurative S.pyogenes complications follow some streptococcal infections and not others?
The strains of S. pyogenes that produce these infections possess virulence factors that other strains don't have.
What is Osteomyelitis?
What is the most common cause of osteomyelitis?
FBP stands for...
Full blood picture.
CRP stands for...
What does a high Erythrocyte Sedimentation Rate (ESR) indicate?
Inflammation somewhere in the body.
What colour are Gram Positives in a blood culture?
What colour are Gram Negatives in a blood culture?
Cellulitis is typically caused by...
Describe the gram stain of Staphylococci
Blue, round cocci arranged in grape like clusters
When do you use the coagulase test, and how does it work?
When you want to identify the species of Staphylococcus. S.aureus will be coagulase positive, as it produces an enzyme called coagulase, which converts fibrinogen to fibrin.
Other species of Staphylococci are coagulase negative
Which Staphylococcus causes urinary tract infections?
Which test do you use to distinguish between staph and strep species?
The catalase test. Streptococci are catalase negative, as they don't contain the enzyme catalase, which converts H2O2 to water and oxygen.
Describe the gram stain of Streptococci
Blue, round cocci generally arranged in pairs (diplococci), or in chains
Describe the difference between alpha-haemolytic and beta-haemolytic steptococci
Alpha - bacteria will only partially digest red blood cells in agar plate
Beta - will fully digest red blood cells in agar plate
How are beta-haemolytic streptococci classified?
By their Lancefield typing.
S.pyogenes is Lancefield A
S.agalactiae is Lancefield B
Does S.pyogenes cause suppurative disease (pus-forming)?
Yes - these include tonsillitis and Otitis media
What are six species of important alpha-haemolytic streptococci?
S.mutans (leading cause dental carries)
S.mitis (non-hospital acquired endocarditis)
S.salvarius (mouth flora, uncommon cause of meningitis)
S.sanguinus (antagonises S.mutans role in dental carries)
S.bovis (GI commensal, can cause endocarditis, bacteraemia and septicaemia)
"Angie Mutated Mighty Saliva, Sanguinely Bored"
Describe the gram stain of S.pneumoniae
Blue, diplococci, lancet-shaped