S. aureus

Question 1

Describe Staphylococci?

Answer 1

gram positive cocci that grow in clusters; non-motile

Question 2

What are the 3 pathogenic species in humans?

Answer 2

S.aureus; s. epidermidis; s. saprophyticus

Question 3

What type of infections does s. saprophyticus?

Answer 3

UTI

Question 4

How can S.aureus be differentiated from S.epidermidis; S.saprophyticus?

Answer 4

S. aureus is coagulase positive whereas otehrs are negative; appaearnce- aureus is yellow vs others are white ; aureus is positive for protein A/clumping factor whereas otehrs are negative

Question 5

Which pathogenic staph species use mannitol (sugar)?

Answer 5

S.aureus and S.saprophyticus

Question 6

Why is S.aureus coagulase positive?

Answer 6

secretes coagulase which leads to localised blood clotting as cleaves prothrombin into thrombin which converts fibrinogen to fibrin

Question 7

What is the main test for differentiating strep vs staph?

Answer 7

all staph are catalse positive whereas strep are negative

Question 8

How does the catalase test work?

Answer 8

if bacteria produce catalase enzyme, are able to convert hydrogen peroxide to water and oxygen- resulting in lots of bubbles

Question 9

What is the function of protein A?

Answer 9

binds Fc region of antibodies, inhibiting their normal function

Question 10

What is the function of clumping factor?

Answer 10

causes clumping of blood plasma

Question 11

What are the ways of differentitating staph. aureus from strep?

Answer 11

microscopy- clusters vs chain; culture: golden pigment of aureus; catalse test

Question 12

What are the diseases the aureus causes by exotoxin release?

Answer 12

gastroenteritis; toxic shock syndrome; staph scalded skin syndrome

Question 13

What is the exotoxin responsible for gastroenteritis?

Answer 13

enterotoxins

Question 14

What exotoxin is responsible for toxic shock syndrome?

Answer 14

TSST-1

Question 15

What exotoxin is responseible for staph scalded skin syndrome?

Answer 15

exfoliation toxin

Question 16

What feature do endotoxins and TSST1 share?

Answer 16

both superantigens

Question 17

What is a superantigen?

Answer 17

binds outside the antigen-binding groove reulsting in APC and T cell binding even wihtout peptide reuslting in hyperactivation of hte immune system

Question 18

What is the target of exoliation toxin?

Answer 18

cleaves desmoglein-1: resulting in disintegration of a layer of skin

Question 19

How is protein A linked to the cell wall?

Answer 19

covalently linked to peptidoglycan

Question 20

What are the functions of peptidoglycan?

Answer 20

shape/structure; protection; platform to anchor surface proteins

Question 21

How is peptidoglycan syntehsised?

Answer 21

by enzymes not the ribosome

Question 22

What enzymes convert a monomer of peptiodglycan to a cross-linked peptidoglycan?

Answer 22

penicillin binding proteins

Question 23

How many penicillin binding proteins does S.aureus have?

Answer 23

4

Question 24

Which is the only PBP to have both transglycosylase and transpeptidase activity?

Answer 24

PBP2

Question 25

what funtion do all PBPs have?

Answer 25

transpeptidase

Question 26

How does the transpeptidase activity of PBPs work?

Answer 26

cleaves a peptide and binds itself (now tetrapeptide- monomer is pentapeptide) covalently then makes another peptide bond to join to another chain

Question 27

Why does penicillin inhibit PBP action?

Answer 27

looks like a PBP substrate to PBP covalently binds and cleaves beta-lactam ring but cannot resolve itself

Question 28

What gene encodes PBP2a?

Answer 28

mecA

Question 29

What causes aureus resistance to penicillin?

Answer 29

beta lactamase

Question 30

What causes aureus resistance to methicillin?

Answer 30

PBP2a which has low affinity for methicillin