Resistance In Gram +ve

Question 1

High priority pathogens (WHO list)

Answer 1

•enterococcus faecium
•staphylococcus aureus

Question 2

Medium priority pathogens (WHO)

Answer 2

•streptococcus pneumoniae

Question 3

Staphylococcus aureus resistance mechanism

Answer 3

•produce beta lactamase
•destroys penicillin

Question 4

Enterococci resistance

Answer 4

•inherent resistance/tolerance

Question 5

Streptococcus Pneumoniae resistance mechanism

Answer 5

•alter Penicillin binding proteins (PBP)
•reduced affinity for beta lactams

Question 6

What is the functions of PBPs (penicillin binding proteins)

Answer 6

•provides cross linking between NAG and NAM in peptidoglycan cell wall

Question 7

How do beta lactam antibiotics affect cell wall

Answer 7

•PBPs recognise D-ala-D-ala
•beta lactams mimic this
•PBPs bind beta lactams instead
•cross linking disrupts

Question 8

What do beta lactamases do

Answer 8

•hydrolyse beta lactam ring between N and O
•creates penicillioc acid instead
•ineffective

Question 9

What is the effective part of penicillins

Answer 9

•the beta lactam ring

Question 10

What is flucloxacillin used for

Answer 10

•beta lactamase producing staphylococci

Question 11

How does flucloxacillin work for staphylococcus but penicillin does not

Answer 11

•became resistant to penicillin
•bulky side chains added to make flucloxacillin prevent beta lactamase from working

Question 12

What is the spectrum of flucloxacillin

Answer 12

•very narrow
•developed for beta lactamase producing staphylococcus

Question 13

What is MRSA

Answer 13

Methicillin resistant staphylococcus aureus

Question 14

How did MRSA begin

Answer 14

•methicillin introduced after penicillin resistance
•s aureus became resistant to methicillin and MRSA spread

Question 15

Mechanism of MRSA resistance

Answer 15

•expression of PBP2a - resists methicillin

Question 16

What encodes for PBP2a

Answer 16

•mecA on staphylococcal chromosomal cassette (SSCmec)

Question 17

What is the target for methicillin resistance tests

Answer 17

•mecA gene on staphylococcal chromosomal cassette

Question 18

What caused the MRSA epidemic

Answer 18

•clonal spread of S. Aureus strains containing SCCmec
•not individual mutations

Question 19

What is SCCmec

Answer 19

•operon in MRSA
•encoding for mecA (PBP2a)

Question 20

How did they reduce MRSA rates

Answer 20

•reporting and surveillance of bacteraemia
•infection control
•bacteraemia targets

Question 21

Bacteraemia meaning

Answer 21

Presence of bacteria in the bloodstream

Question 22

What can enterococci cause

Answer 22

•UTI
•bowel sepsis

Question 23

What enterococci make up >90% of human isolates of enterococcus

Answer 23

•E. Faecalis
•E. Faecium

Question 24

How are enterococci tolerant

Answer 24

•contain PBPs with low affinity for beta lactams and glycopeptides
•inhibited by clinical concentrations
•only killed if excess of MIC

Question 25

Synergy meaning

Answer 25

Cooperation of >1 substances to produce combined effect better than if individual

Question 26

How can enterococci tolerance be overcome

Answer 26

•synergy •combine cell walls active agent with aminoglycoside

Question 27

Antibiotic combination to treat enterococci

Answer 27

•gentamicin + penicillin or vancomycin

Question 28

What is E. Faecium resistant to

Answer 28

Vancomycin

Question 29

What are the 6 phenotypes for vancomycin resistance

Answer 29

•VanA-G

Question 30

Clinically significant vancomycin resistant phenotypes

Answer 30

VanA and VanB

Question 31

Most common vancomycin resistant phenotype

Answer 31

VanA

Question 32

How many genes does the VanA/B phenotype contains

Answer 32

•7 genes in 2 clusters (VANA +VANB)

Question 33

Describe VanA resistance

Answer 33

•high resistant to vancomycin and teicoplanin •alter PBP - D-ala-D-ala becomes D-ala-D-lac

Question 34

Describe VanB resistance

Answer 34

•variable resistance to vancomycin •susceptible to teicoplanin

Question 35

What is VRE

Answer 35

Vancomycin resistant enterococci

Question 36

How does/did VRE evolve

Answer 36

High risk patients who have been treated with glycopeptides *incorrect antibiotic use rather than infection control like MRSA

Question 37

How to mediate VRE

Answer 37

Antibiotic stewardship

Question 38

Main places/treatments where VRE evolves

Answer 38

•Haemodialysis •Haematology •Critical Care

Question 39

Treatments for VRE

Answer 39

•quinupristin-dalfopristin •linezolid •daptomycin •tigecycline

Question 40

What is VRSA

Answer 40

•S. Aureus aquired VanA gene found in enterococci

Question 41

How do pneumococcals become resistant to beta-lactams

Answer 41

•alter PBPs •alters to PBP types - 2x, 2b, 1a

Question 42

Six PBPs S. Pneumonia contains

Answer 42

•1a, 1b, 2a, 2b, 2x, 3

Question 43

What is standard treatment for meningitis

Answer 43

•cephalosporin (ceftriaxone)

Question 44

How are pneumococci resistant to cephalosporin

Answer 44

•alterations of PBP - 1a, 2x

Question 45

Treatments for childhood meningitis - with previous antibiotic use or travel out of the UK in past 3 months

Answer 45

Vancomycin