Common Mechanisms of Bacterial Resistance Flashcards
When is an organism considered resistant?
When the organism is unlikely to respond to attainable levels of that drug in tissues.
What are the different types of microbial resistance?
Inherent Resistance
Acquired Resistance
What is inherent resistance?
Natural resistance to an antibiotic. This resistance is usually due to the inability of the drug to penetrate the bacterial cell wall.
What is acquired resistance?
Resistance that may be present in some strains but not in others, so needs to be subjected to laboratory sensitivity testing.
How is bacterial resistance acquired?
1.)A spontaneous mutation during multiplication of bacterial DNA can result in a change in structure or function which no longer allows the antibiotic to act as its target may have changed.
2.)The gene or genes that code for resistance can spread from organism to organism or indeed from species to species.
This is the most common method of resistance spread. Genes usually carried on plasmids or on transposons.
What are the 2 methods of resistance to beta lactam antibiotics?
- ) beta lactamase production
2. ) Alteration of penicillin binding protein (PBP) target site
What is beta lactamase?
Bacterial enzymes which cleave beta lactam ring of the antibiotic, rendering it inactive.
What are the 2 ways to combat beta lactamase?
- Introduce a second component to the antibiotic which is a beta lactamase inhibitor, so protects the antibiotic from enzymatic degradation.
- modify the antibiotic side chain to produce an antibiotic which is resistant to the actions of beta lactamase.
Why are extended spectrum beta lactamses an increasing problem in hospitals?
They are produced by some gram negative organisms. They can break down 3rd generation cephalosporins as well as penicillins rendering them resistant to all beta lactam antibiotics.
What are CPE?
Carbapenemase Producing Enterobacteriaceae - an extremely resistant gram negative organism, resistant to carbapenem.
What are Penicillin Binding Proteins (PBPs)?
The enzymes which are involved in peptidogylcan synthesis and which are inhibited by the binding of penicillins and cephalosporins.
What does a mutation in a PBP cause?
Results in a modified target site to which beta-lactams will no longer bind.
Some can be resistant to all beta lactams.
What antibiotic is beta lactamase resistant and so is used to treat resistant staphylococcus aureus?
Flucloxacillin
What is MRSA resistant to?
Penicillin and cephalosporins.
Outline glycopeptide resistance.
- Previously unheard of (very unusual in gram positives)
- However vancomycin resistant enterococci have emerged.
(peptidoglycan precursor to which vancomycin used to bind has been altered).
