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RACP Written 2018 > Infectious Diseases - Antibiotic Resistance > Flashcards

Infectious Diseases - Antibiotic Resistance Flashcards

1
Q

cfr gene

A

cfr gene = chloramphenicol/ florpenicol resistant

Seen in some staph to make resistant to LINEZOLID

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2
Q

VRE is most commonly faecium or faecalis?

A

Faecium is more commonly resistant

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3
Q

VRE: which genotype is most common?

A

In South Australia: Van B

In Eastern Australia and USA: Van A

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4
Q

What are the mechanisms for antibiotic resistance?

A

Tranduction (bacterial specific viruses transfer DNA between closely related bacteria)

Transformation (parts of DNA taken up by bacterium from external environment)

Conjugation (direct cell-cell contact between bacteria)

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5
Q

What are the ESKAPE organisms?

A

= highly resistant species

Enterococcus Faecium
Staph Aureus
Klebsiella pneumonia
Acinetobacter baumanii
Pseudomonas aeruginosa
Enterobacter sp.
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6
Q

Which Ambler Class of Beta Lactamases are structurally unrelated to PBPs and what mineral are they dependent on?

A

Class A

Zinc-dependent

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7
Q

Class A Beta Lactamases

  • examples?
  • what additional therapy do they lend themselves to?
A

ESBLs
Carbapenemases
Penicillinases

Inhibited by clavulanate (beta lactamase inhibitors) which get preferentially hydrolised instead of antibiotics

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8
Q

Class B Beta Lactamases

  • examples?
  • inhibited by what?
A

Metalloenzymes

Broadest spectrum (hydrolise ALL beta lactamases except aztreonam)

Inhibited by chelating agents

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9
Q

Class C Beta Lactamases

- examples?

A

AmpC enzymes which preferentially hydrolyse cephalosporins and are NOT inhibited by clavulanate

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10
Q

What are ESCAPPM Organisms?

A

Chromosomally mediated beta lactamases:

Enterobacter sp
Serratia sp
Citrobacter sp
Acinetobacter sp
Pseudomonas aeruginosa
Proteus vulgaris
Morganella morganii
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11
Q

Which organisms have ESBL?

How do you treat them?

A

E coli and Klebsiella most commonly
(also in Enterobacter and Acinetobacter)

Treat with meropenem, irtapenem and cotrimoxazole

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12
Q

What does NDM-1 do?

How do you treat?

A

Encodes carbapenemases
In klebsiella and E coli

Treat with polymyxins and tigecycline

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13
Q

Risk factors for NDM-1 organism?

A

Travel
Hospitalisations
Puddles and tap water
Sweedish backpackers

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14
Q

A question mentions sweedish backpackers and puddles…what antibiotic resistance mechanism do you suspect?

A

NDM-1

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15
Q

What is KPC antibiotic resistance?

A

KPC encodes a carbapenemase produced by Klebsiella
Gene is blaKPC

Variable resistance to colistin

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16
Q

What gene encodes KPC?

A

blaKPC

17
Q

What is GelE antibiotic resistance mechanism?

A

E faecalis produces metalloproteinase GelE which degrades E cadherin.

18
Q

Some bacteria are resistant via altered binding sites. Describe these four mechanisms

A

1) Altered ribosomal target site
ie: resistance to streptomycin (30s)
resistance to erythromycin (50s)
cfr gene (chloramphenicol/florpenicol resistance) in some staph which make them resistant to linezolid

2) Altered cell wall precursor targets
ie: VRE

3) Altered target enzymes
ie: altered PBPs in penicillin resistant strep pneumonia

4) Altered protection of target sites

19
Q

How does VRE make antibiotic resistance?

A

VRE (mainly Enterococcus faecium, not faecalis)
substitutes D-lac for D-alanine in lipid 11

Other forms replace D-ala with D-serine which reduces vancomycin efficacy

20
Q

How is VRE resistance obtained by bacteria?

A

Plasmid or transposins

21
Q

In SA what type of VRE do we have?

Which is more common in Eastern states?

A

Usually Van-B type of VRE in SA

But most commonly in Eastern states and USA is Van-A

22
Q

Relationship between Van A VRE and teicoplanin?

A

Van A is ALWAYS resistant to teicoplanin, and is induced by glycopeptides like teicoplanin

23
Q

How do we treat VRE?

A

Treat with amoxicillin (faecalis often sensitive, NOT faecium)

Linezolid
Teicoplanin (but ONLY if Van B)
Synercid (ONLY faecium)
Daptomycin
Fosfomycin
24
Q

What is optrA gene?

A

optrA gene found in E faecalis and E faecium results in OXAZOLIDIONE resistance

25
Q

What is NORSA?

A

Community-acquired, non-multiresistant oxacillin-resistant Staphylococcus aureus (NORSA)

Causes necrotizing pneumonia and skin infections

  • usually sensitive to clindamycin, bactrim, macrolides and gentamicin
26
Q

What is the mechanism by which MRSA is resistant?

A

MRSA is due to mecA gene encoding PBP2a protein with low affinity for beta lactam antibiotics

27
Q

What is VISA MRSA?

How do you treat it?

When is it more commonly encountered?

A

MRSA with reduced vancomycin sensitivity

Associated with thickened cell wall containing vanc-binding dipeptides which detain the drug (so more targets for D-ala-D-ala)

Treat with linezolid or rifampicin

Especially in dialysis or Left Ventricular Devices

28
Q

What are the anti-MRSA cephalosporins?

A

Ceftaroline and Ceftobiprole

29
Q

What are the new MRSA treatments?

A

DALBAVANCIN: noninferior to vanc followed by linezolid

TELAVANCIN

TEDIZOLID = oxazolidinone with less haem adverse effects

30
Q

What is CRE?

How do you treat?

A

= carbapenam resistant enterobacteriae
ie: E coli, klebsiella, salmonella, shigella, enterobacter

Treat with colistin, tigecycline or fosfomycin

31
Q

What creates colistin resistance?

A

mcr-1 gene (plasmid mediated) in enterobacteriae

adds phosphoethanolamine to lipid A in colistin

32
Q

What is most commonly carbepenem resistant?

A

Acinetobacter baumanii

33
Q

What mechanisms create ANTIBIOTIC RESISTANCE via DECREASED PERMEABILITY?

A

Outer membrane permeability:
- ie mutations causing loss of porins

Inner membrane permeability
- ie aminoglycoside resistance

34
Q

What antibiotics are susceptible to ANTIBIOTIC RESISTANCE via ACTIVE EFFLUX?

A

Linezolid
- natural lack of activity of linezolid against gram negatives is due to efflux pump

Tetracyclines
- resistance in gram negatives due to efflux of tetracyclines

Macrolides and Streptogramins
- in some strains of s pneumonia, strep pyogenes, staph aureus and strep epidermidis

Beta lactams
- in pseudomonas

Fluoroquinolones
- in enteric bacteria and staph

35
Q

What is the c diff hypervirulent strain?

A

B1/NAP1/027 is resistant to fluoroquinolones

36
Q

What is GYR mutation?

A

GYR mutation in E coli resistant to cipro

RACP Written 2018 (167 decks)

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