Lecture 13. Key Gram Positive Superbug - Staphylococcus aureus

Question 1

What is the only molecule that Streptococcus aureus can code for?

Answer 1

Coagulase

Question 2

What is catalase used for?

Answer 2

Distinguishing between Staphylococcus and Streptococcus bacteria
Catalase protects Staphylococcus from reactive oxygen species

Question 3

What are the (likely) reasons for the reduction in MRSA cases in Europe?

Answer 3

Improved screening of hospitalised patients
Better infection-control practices (isolating patients who have MRSA)
Better barrier precautions (doctors wearing sterile gowns)

Question 4

Where did the majority of MRSA associated deaths occur in Wales between 2010-14?

Answer 4

92.7% NHS hospital (being hospitalised is a risk factor)

Question 5

What are reservoirs of MRSA?

Answer 5

Healthcare-associated MRSA
Livestock-associated MRSA
Community-associated MRSA
Fomite-associated MRSA

Question 6

What is a significant risk for subsequent S. aureus?

Answer 6

Colonisation of the nares

Question 7

In >80% of S.aureus bacteraemais, the infecting strain is identical to what?

Answer 7

Nasal colonising strain detected prior to onset of bacteraemia

Question 8

How long can MRSA survive on sterile goods?

Answer 8

More than 38 weeks

Question 9

How has the epidemiology of MRSA changed?

Answer 9

Previously most patients became colonised with MRSA in hospitals: many patients now become colonised in the community (e.g. nursing homes), [community acquired MRSA (CA-MRSA)]

Question 10

What are examples of community-associated MRSA being spread by frequent skin to skin contact?

Answer 10

Sports participants
Men who have sex with men (MSM)
Living in crowded conditions: inmates in prisons,
military recruits, children in daycare, elderly in care centres
Having or touching cut/grazed skin

Question 11

What are examples of community-associated MRSA being from fomites?

Answer 11

Sharing common personal items e.g. towels and razors
Touching contaminated surfaces

Question 12

What are other risk factors in the spread of community-associated MRSA?

Answer 12

Being HIV positive
Getting tattooed

Question 13

What was detected in 98% of MRSA isolates?

Answer 13

SCCmec type IV and the PVL toxin gene

Question 14

What is staphylococcal cassette chromosome mec (SCCmec)?

Answer 14

A mobile genetic element of Staphylococcal bacteria. Includes the mecA gene (resistance to methicillin): the only known way to spread this gene is by horizontal gene transfer

Question 15

What is Panton-Valentine leukocidin (PVL)?

Answer 15

An exotoxin that stimulates apoptosis of granulocytes and monocytes and secrets an α-toxin

Question 16

What is Clone USA300?

Answer 16

MRSA that has upregulation of multiple virulence factors, and secretes an α-toxin that stimulates apoptosis of T cells, B cells, and Monocytes as well as PVL

Question 17

How were incidence of USA300 reduced?

Answer 17

General control measures for MRSA

Question 18

How did S. aureus become highly resistant to methicillin?

Answer 18

High level resistance to methicillin developed by the acquisition of a completely new PBP – PBP2’ encoded by mecA –with a very low affinity for methicillin

Question 19

What is the antibiotic of choice for treating MRSA infections?

Answer 19

The glycopeptide vancomycin

Question 20

When was vancomycin resistance first detected?

Answer 20

1997: VISA - vancomycin intermediately susceptible S. aureus - first isolated in Japan, causing widespread alarm