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Flashcards in S. aureus Deck (30):
1

Describe Staphylococci?

gram positive cocci that grow in clusters; non-motile

2

What are the 3 pathogenic species in humans?

S.aureus; s. epidermidis; s. saprophyticus

3

What type of infections does s. saprophyticus?

UTI

4

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

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

5

Which pathogenic staph species use mannitol (sugar)?

S.aureus and S.saprophyticus

6

Why is S.aureus coagulase positive?

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

7

What is the main test for differentiating strep vs staph?

all staph are catalse positive whereas strep are negative

8

How does the catalase test work?

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

9

What is the function of protein A?

binds Fc region of antibodies, inhibiting their normal function

10

What is the function of clumping factor?

causes clumping of blood plasma

11

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

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

12

What are the diseases the aureus causes by exotoxin release?

gastroenteritis; toxic shock syndrome; staph scalded skin syndrome

13

What is the exotoxin responsible for gastroenteritis?

enterotoxins

14

What exotoxin is responsible for toxic shock syndrome?

TSST-1

15

What exotoxin is responseible for staph scalded skin syndrome?

exfoliation toxin

16

What feature do endotoxins and TSST1 share?

both superantigens

17

What is a superantigen?

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

18

What is the target of exoliation toxin?

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

19

How is protein A linked to the cell wall?

covalently linked to peptidoglycan

20

What are the functions of peptidoglycan?

shape/structure; protection; platform to anchor surface proteins

21

How is peptidoglycan syntehsised?

by enzymes not the ribosome

22

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

penicillin binding proteins

23

How many penicillin binding proteins does S.aureus have?

4

24

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

PBP2

25

what funtion do all PBPs have?

transpeptidase

26

How does the transpeptidase activity of PBPs work?

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

27

Why does penicillin inhibit PBP action?

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

28

What gene encodes PBP2a?

mecA

29

What causes aureus resistance to penicillin?

beta lactamase

30

What causes aureus resistance to methicillin?

PBP2a which has low affinity for methicillin