Lecture 32 - Staph Aureus

Question 1

Features of Staph aureus
1)
2)
3)

Answer 1

1) Gram + cocci
2) Non-motile
3) Facultative anaerobes

Question 2

Where does Staph aureus normally inhabit?
1) 
2) 
3) 
4)

Answer 2

1) URT
2) Skin
3) Vagina
4) Intestine

Question 3

Examples of SA virulence factors
1) 
2) 
3) 
4)
5)
6)
7)

Answer 3

1) Exfoliative toxins
2) Enterotoxins
3) Haemolysins
4) Lipases, proteases, DNAases
5) Leukocidins
6) Protein A
7) Beta-lactamase

Question 4

Protein A

Answer 4

Binds Fc of IgG

Question 5

Most common serious SA infections
1)
2)
3)

Answer 5

1) Haematogenous spread
2) Endocarditis
3) Osteomyelitis

Question 6

How long did it take SA to become resistant to penicillin?

Answer 6

1-2 years

Question 7

How long did it take SA to become resistant to methicillin?

Answer 7

Under 1 year

Question 8

How long did it take for 25% of SA in hospitals to be resistant to penicillin?

Answer 8

6 years

Question 9

How long did it take for 25% of SA in hospitals to be resistant to methicillin?

Answer 9

20 years

Question 10

Is MRSA more or less virulent than normal SA?

Answer 10

Less virulent

Question 11

Number of people in the USA who are colonised with SA

Answer 11

89.4 million

Question 12

When is SA most dangerous?

Answer 12

When it gets into the bloodstream, causes metastatic infections (endocarditis, osteomyelitis/septic arthritis, discitis/epidural abscesses)

Question 13

SA bacteraemia incidence in Australia

Answer 13

35/100,000 people

Question 14

ANZCOSS
1)
2)
3)

Answer 14

1) Australia New Zealand Cooperative on Outcomes in Staphylococcal sepsis
2) Prospective observational cohort study of Staph bloodstream infections
3) Shows that chance of dying of staph bacteraemia increases with age

Question 15

Size of SA genome

Answer 15

2.8MB

Question 16

Proportion of SA genome that is core genome

Answer 16

~75%

Question 17

Amino acid conservation of core genome between SA strains

Answer 17

98-100%

Question 18

Contents of SA core genome
1) 
2) 
3) 
4)
5)
6)
7)

Answer 18

1) Central metabolism
2) Hose keeping
3) Protein A
4) Capsule
5) Coagulase
6) Protease
7) Fibrinogen-binding proteins

Question 19

How can the accessory genome be constructed?
1) 
2) 
3) 
4)

Answer 19

1) Phage
2) Genomic islands
3) Pathogenicity islands
4) Plasmids and transposons

Question 20

Contents of pathogenicity islands in SA
1)
2)

Answer 20

Superantigens, such as

1) tst
2) Enterotoxins

Question 21

Contents of transposons and plasmids in SA accessory genome

Answer 21

Antibiotic resistance genes

Question 22

Staphylococcal cassette chromosome

Answer 22

Contains mecA

Question 23

What is the Staphylococcal cassette chromosome found in?

Answer 23

MRSA

Question 24

In the Artemis tool, what show up as blue?

Answer 24

Parts of the accessory genome

Question 25

Is high-level vancomycin resistance common in SA?

Answer 25

No. Quite rare

Question 26

What confers high-level vancomycin resistance?

Answer 26

VanA from VRE

Question 27

What does the VanA gene do?
1)
2)

Answer 27

1) Confers high-level vancomycin resistance

2) Encodes a ligase that replaces d-ala-d-ala with d-ala-d-lac

Question 28

High-level vancomycin resistance MIC

Answer 28

Over 16mg/L

Question 29

Where does vancomycin act in bacteria?

Answer 29

High rate of diffusion through the division septa of bacteria.
Where new cell wall is made

Question 30

Vancomycin intermediate Staph aureus (VISA) vancomycin MIC

Answer 30

4-8mg/L

Question 31

A way to measure vancomycin resistance in SA

Answer 31

Population analysis

Question 32

What is population analysis?

Answer 32

Culture SA in different concentrations of vancomycin, see how many colonies grow. Can be used to calculate MIC

Question 33

What is the VISA phenotype associated with?

Answer 33

Cell wall thickening

Question 34

Last-resort antibiotic for MRSA treatment

Answer 34

Linezolid

Question 35

What are GraS, VraS?
1)
2)
3)

Answer 35

1) Membrane-bound sensors in SA
2) 2-component regulators
3) Might be activated in response to vancomycin, contribute to VISA phenotype

Question 36

SA 2 component regulators

Answer 36

1) GraS

2) VraS

Question 37

How do GraS and VraS work?
1)
2)

Answer 37

1) Sensor regions detect a stimulus

2) VraR, GraR bind to DNA, change transcription

Question 38

Effects of stimulating VraS and GraS
1)
2)
3)
4)
5)

Answer 38

1) Alanation of membrane teichoic acids increases +ve charge of membrane, reducing vancomycin diffusion
2) Thickening of cell wall
3) Decrease in exotoxin production
4) Reduced protein A
5) Increased capsule

Question 39

Is VISA very common?

Answer 39

Not at the moment.

It is likely to become more common

Question 40

How does VISA evolve?

Answer 40

Appears to accumulate mutations in regulatory genes

Question 41

walR gene
1)
2)
3)

Answer 41

1) A 2 component regulator
2) Controls cell wall synthesis
3) Present in division septum cell wall

Question 42

Effect of mutant walR 
1)
2)
3)
4)

Answer 42

1) Might be responsible for VISA phenotype
2) Mutation of A to G changes lysine to arginine
3) Reduced autolysin production
4) Increased cell wall production

Question 43

Autolysin role

Answer 43

Involved in cell wall turnover in SA

Question 44

How do we know that mutant walR is responsible for VISA?

Answer 44

Koch’s molecular postulates (gene removed, lost VISA. Gene placed in vanc-sensitive SA, became VISA)