1-30 Mechanisms of Resistance to Antibiotics Flashcards Preview

MSI Unit I > 1-30 Mechanisms of Resistance to Antibiotics > Flashcards

Flashcards in 1-30 Mechanisms of Resistance to Antibiotics Deck (23)

Intrinsic resistance

innate to resist activity of an abx due to inherent structural or functional characteristics
Ex) M.Tuberculosis, Pseudomonas aeruginosa


Mutational Resistance

resistance may occur due to chromosomal mutation that is spontaneous or random
Mutability depends on structure and number of genes in which mutations can produce selectable phenotype


Acquired Resistance

Acquired resistance - occurs when microorganism obtains ability to resist activity of abx to which it was previously susceptible.

Acquisition of gene(s) conferring resistance through horizontal gene transfer (process of swapping genetic material between neighboring bacteria)


Cite the differences among transformation, transduction, and conjugation with respect to how bacteria acquire extrachromosomal DNA

a. Tranformation - involves uptake of shore fragments of naked DNA

Transduction - involves transfer of DNA from one bacteria into another via bacteriophages

Conjugation - involves transfer of plasmids via sexual pilus, requires cell-cell contact


Major Mechanisms by which bactera can be resistant to antibiotics(7)

1. enzymatic inactivation (beta lactamase)

2. Efflux (push out)

3. Alteration of Target Site (MRSA PBP2->PBP2a)

4. protection of target site

5. overproduction of target

6. bypass of inhibited process

7. decreased permeability


4 classes of beta lactamases

narrow spectrum beta lactamases, extended spectrum beta lactamases (ESBLs), Amp C Beta lactamases, carbepenemases


describe beta lactamase

enzyme inactivates ring by splitting the amide bond



most common producers?

treat with?

extended Spectrum Beta Lactamases - enzymes that mediate resistance against 3rd and 4th generation cephalosporins

Klebsiella, E.coli, and Proteus.

May treat with carbepenem


Amp C beta lactamases


chromosomal enzymes that confer resistance to penicillins, narrow spectrum cephalosporins.

i. Not susceptible to beta lactamase inhibitors
ii. Members of enterobacteriaceae except Klebsiella and E.coli
iii. Has been introduced into plasmids



produced by?

largest resistance, hydrolyze carbepenems but also broad spectrum penicillins

i. Klebsiella pneumonia carbapenemases (KPC) and resistant enterobacteriaceae (CRE)


Discuss the action of beta lactamase inhibitors.

two examples

They have a beta lactam ring which beta lactamases preferentially bind to. Not antimicrobic

clavulanate/clavulanic acid


how are antibiotic genes typically transferred?

mainly through conjugation


what are transposons?

jumping genes, can jump from one place on chromosome to another, from one plasce on plasmid to antoher, or chromosome to plasmid.

Some organsisms are hard wired - but what is this gene picks up the excision and incision sequences? Turns into a transposon. What was once a "hard wired" gene, can now be found on plasmid


insertion sequences

have own promoters. Are mobile genetic elements that are known to encode only fuctions involved in insertion events.

May contain partial or complete, alllow activation of downstream genes



Integrons - gene capturing machine. Little sequences with promoter sequences with a binding site (atttl1). The chomosomal casette comes insid ecell, gets into integron, unfolds, binds. Can also have many in a row.


Impact of integron-borne promoter region

The expression of cassette-associated resistance genes is influenced by their position in an integron and proximity to the promoter sequence and the number of cassettes in the integron.


as bacteria are exposed to antibiotics..

can take genes from promoter to now upregulate resistnace genes. (rpeviously sensitive, now resistance).


why would you ever want resistance genes downregulated?

Being resistant is energy internsive. If you don’t need to be promoting a beta lactamase, turn it off. Being attacked? Turn it back on (upregulate)


how to treat staph aureus?

it produces beta lactamase

give script for both inhibitor and antibiotic, such as augmentin


procedure if a patient has CRE's?


contact plus - strict isolation


describe carbepenemase

Carbepenam-hyrolyzing beta lactamases (produced by CRE's - carbepenem resistant enterobacetre) - most diverse of all beta lactamases
-recognize and hydrolyze all beta lactamaes
-started of as kleb chromosome, turned into a trasnposon


how to treat MRSA



what antibiotics are effective against ESBL producing strains of bacteria?


Decks in MSI Unit I Class (52):