L4 - Gram Positive Cocci

Question 1

What is the mechanism of action of the B-Lactam antibiotics?

Answer 1

They interfere with cell-wall synthesis through a bacterial enzyme called transpeptidase.

Question 2

Describe the mechanism of resistance of MRSA strains of Staphylococcus aureus to the isoxazolyl penicillins.

Answer 2

They have acquired a gene called mecA which encodes for a transpeptidase, PBP2a.

Question 3

Name 3 non-suppurative complications of Streptococcus pyogenes infection.

Answer 3

Scarlet fever, Rheumatic fever and acute post-streptococcal glomerulonephritis.

Question 4

Why do non-suppurative S.pyogenes complications follow some streptococcal infections and not others?

Answer 4

The strains of S. pyogenes that produce these infections possess virulence factors that other strains don’t have.

Question 5

What is Osteomyelitis?

Answer 5

Bone infection.

Question 6

What is the most common cause of osteomyelitis?

Answer 6

Staphylococcus aureus.

Question 7

FBP stands for…

Answer 7

Full blood picture.

Question 8

CRP stands for…

Answer 8

C-Reactive protein.

Question 9

What does a high Erythrocyte Sedimentation Rate (ESR) indicate?

Answer 9

Inflammation somewhere in the body.

Question 10

What colour are Gram Positives in a blood culture?

Answer 10

Bluish purple.

Question 11

What colour are Gram Negatives in a blood culture?

Answer 11

Pink.

Question 12

Cellulitis is typically caused by…

Answer 12

Streptococcus pyogenes.

Question 13

Describe the gram stain of Staphylococci

Answer 13

Blue, round cocci arranged in grape like clusters

Question 14

When do you use the coagulase test, and how does it work?

Answer 14

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

Question 15

Which Staphylococcus causes urinary tract infections?

Answer 15

Staphylococcus saprophyticus

Question 16

Which test do you use to distinguish between staph and strep species?

Answer 16

The catalase test. Streptococci are catalase negative, as they don’t contain the enzyme catalase, which converts H2O2 to water and oxygen.

Question 17

Describe the gram stain of Streptococci

Answer 17

Blue, round cocci generally arranged in pairs (diplococci), or in chains

Question 18

Describe the difference between alpha-haemolytic and beta-haemolytic steptococci

Answer 18

Alpha - bacteria will only partially digest red blood cells in agar plate
Beta - will fully digest red blood cells in agar plate

Question 19

How are beta-haemolytic streptococci classified?

Answer 19

By their Lancefield typing.
S.pyogenes is Lancefield A
S.agalactiae is Lancefield B

Question 20

Does S.pyogenes cause suppurative disease (pus-forming)?

Answer 20

Yes - these include tonsillitis and Otitis media

Question 21

What are six species of important alpha-haemolytic streptococci?

Answer 21

S.angionis (abscesses)
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”

Question 22

Describe the gram stain of S.pneumoniae

Answer 22

Blue, diplococci, lancet-shaped

Question 23

What are the two important species of enterococci, where do they reside, and what is their gram stain?

Answer 23

Enterococci faecium & Enterococci faecalis
Human bowel commensal flora
Gram positive, diplococci in chains