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17 Cards in this Set

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Constitutive vs Inducible?
B-lactamases can be constituitively (constantly) expressed, or Induced expression (eg by antibiotics)
What are the B-lactamase classifications?
Ambler (based on differences in amino acid sequences)
Bush-Jacoby (based on different substrates/B-lactams)
Which B-lactamase classes are plasmid mediated?
Bush-Jacoby Class 1 (and most of class 2 and 3)
What is the most problematic B-lactamase class?
Bush-Jacoby Class 2be
Whats a "stably derepressed mutant"?
Bacteria that have a mutation that inhibits the inhibtion of their own B-lactamase production.
They now produce B-lactamase constituitively when induced by an antibiotic.
Give example(s) of bacteria that tend to have more stably derepressed mutants.
Give example(s) of B-Lactams that tend to induce derepressed mutants.
Whats the classic example of a drug that induces a stably derepressed mutant?
SPICE organisms
Known inducers of Bush class 1 chromosomal B-Lactamases: Cefoxitin, Imipenem, (3rd gen cephs: cefotaxime,ceftriaxone,ceftazidime)
Classic ex: Ceftazidime inducing an Enterobacter mutant
Note: The stably derepressed mutation is associated with bush class 1 chromosome B-Lactamase genes, not with other classes like class 2be plasmid B-Lactamase genes (seen in ESBLs).
List all the SPICE organisms
Serratia
P. aeruginosa
Indole + Proteus
Citrobacter
Enterobacter
"SPICE"
If class 1 chromosomal B-lactamases are suspected, which antibiotics should NOT be given to the px?
3rd gen cephalosporins(me: cefotaxime,ceftriaxone,ceftazidime)
Piperacillin/Tazobactam(Tazo cant inhibit these B-Lactamases)
Note: Cefoxitin and Imipenem werent mentioned, but IBLV you would also not give these.
If class 1 chromosomal B-lactamases are suspected, which antibiotics SHOULD be given to the px?
Cefepime (4th gen)
Carbapenems
These are just more stable to the class 1 chromosomal B-lactamases than other antibiotics.
Q: Since SPICE organisms are associated with class 1 chromosomal B-Lactamases, are carbapenems and cefepime the goto drugs for SPICE organisms?
What are ESBLs, and which bugs have them?
Extended Spectrum B-lactamases
Produced by K. pneumonia and E. coli
Bush class 2be (from mutant 2b genes)
IBLV theyre more problematic because they hydrolize a wider spectrum of B-Lactams, and because the genes are on a plasmid they're more transferable.
When ESBL producing organisms are suspected, which antibiotics should be avoided?
3rd gen cephalosporins
Aztreonam (monobactam)

Note: This is just like when we asked about which antibiotics should be avoided when bush class 1 chromosomal B-Lactamases are suspected, here we're concerned with bush class 2b and 2be plasmid B-Lactamases.
Note: The bush classifications are just a way of grouping B-Lactamase genes, but we associate microorganisms with these classes because they contain some of these genes.
When ESBL producing organisms are suspected, which antibiotics should be used?
Carbapenems(drug of choice)
The higher Bush class 2's and the Bush class 3's are ______
Genes that code for Carbapenemases (enzymes that break down carbapenems).
So you cant use carbapenems against the high class 2b or any of the class 3 bacteria. But you want to use them for class 1, and class 2b/2be.
Whats the most dominant B-lactamase gene in the world?
CTX-M
How do bacteria dec their permeability to pcns?
They downregulate their expression of porins so pcns have fewer "doors" to enter(for gram - only).
What are these: MexAB-OprM, MexCD-OprJ, MexEF-OprN, MexXY-OprM?
Genes for (over expressed) efflux pumps produced by just one bacteria (P. aeruginosa)
What kind of resistance do efflux pumps confer?
Besides over-expression leading to very active efflux of drugs, each pump can pump out a broad spectrum of drugs confering multi-drug resistance to that bacterium