Infectious Diseases - Antibiotic Resistance Flashcards
(36 cards)
cfr gene
cfr gene = chloramphenicol/ florpenicol resistant
Seen in some staph to make resistant to LINEZOLID
VRE is most commonly faecium or faecalis?
Faecium is more commonly resistant
VRE: which genotype is most common?
In South Australia: Van B
In Eastern Australia and USA: Van A
What are the mechanisms for antibiotic resistance?
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)
What are the ESKAPE organisms?
= highly resistant species
Enterococcus Faecium Staph Aureus Klebsiella pneumonia Acinetobacter baumanii Pseudomonas aeruginosa Enterobacter sp.
Which Ambler Class of Beta Lactamases are structurally unrelated to PBPs and what mineral are they dependent on?
Class A
Zinc-dependent
Class A Beta Lactamases
- examples?
- what additional therapy do they lend themselves to?
ESBLs
Carbapenemases
Penicillinases
Inhibited by clavulanate (beta lactamase inhibitors) which get preferentially hydrolised instead of antibiotics
Class B Beta Lactamases
- examples?
- inhibited by what?
Metalloenzymes
Broadest spectrum (hydrolise ALL beta lactamases except aztreonam)
Inhibited by chelating agents
Class C Beta Lactamases
- examples?
AmpC enzymes which preferentially hydrolyse cephalosporins and are NOT inhibited by clavulanate
What are ESCAPPM Organisms?
Chromosomally mediated beta lactamases:
Enterobacter sp Serratia sp Citrobacter sp Acinetobacter sp Pseudomonas aeruginosa Proteus vulgaris Morganella morganii
Which organisms have ESBL?
How do you treat them?
E coli and Klebsiella most commonly
(also in Enterobacter and Acinetobacter)
Treat with meropenem, irtapenem and cotrimoxazole
What does NDM-1 do?
How do you treat?
Encodes carbapenemases
In klebsiella and E coli
Treat with polymyxins and tigecycline
Risk factors for NDM-1 organism?
Travel
Hospitalisations
Puddles and tap water
Sweedish backpackers
A question mentions sweedish backpackers and puddles…what antibiotic resistance mechanism do you suspect?
NDM-1
What is KPC antibiotic resistance?
KPC encodes a carbapenemase produced by Klebsiella
Gene is blaKPC
Variable resistance to colistin
What gene encodes KPC?
blaKPC
What is GelE antibiotic resistance mechanism?
E faecalis produces metalloproteinase GelE which degrades E cadherin.
Some bacteria are resistant via altered binding sites. Describe these four mechanisms
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
How does VRE make antibiotic resistance?
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
How is VRE resistance obtained by bacteria?
Plasmid or transposins
In SA what type of VRE do we have?
Which is more common in Eastern states?
Usually Van-B type of VRE in SA
But most commonly in Eastern states and USA is Van-A
Relationship between Van A VRE and teicoplanin?
Van A is ALWAYS resistant to teicoplanin, and is induced by glycopeptides like teicoplanin
How do we treat VRE?
Treat with amoxicillin (faecalis often sensitive, NOT faecium)
Linezolid Teicoplanin (but ONLY if Van B) Synercid (ONLY faecium) Daptomycin Fosfomycin
What is optrA gene?
optrA gene found in E faecalis and E faecium results in OXAZOLIDIONE resistance
