البكتيريا المراوغة Flashcards
Bacteria are capable of becoming resistant through several mechanisms
- Decreased Permeability
- Efflux Pump
- Degrading enzyme
- Alteration in target molecule
Increase efflux
Pumping out the antibiotic faster than it gets in
Give me example about antibiotic that resistance by Increase efflux
tetracyclines
Give me example about antibiotic that resistance by Reduce cellular uptake / Decreased the penetration
imipenem
Reduce cellular uptake
membrane becomes impermeable for antibiotic
Inactivation of the drug (Degrading enzyme)
some bacteria have enzymes that cleave or modify antibiotics
Give me example about antibiotic that resistance by Inactivation of the drug / Degrading enzyme
b lactamase inactivates penicillin and cephalosporin
Alteration of the target site
antibiotic cannot bind to its intended target because the target itself has been modified
Resistance has two types mey be :
- Inherent, intrinsic or innate resistance :
The properties of the bacterium are responsible for preventing the antibiotic action. - Acquired or extrinsic resistance :
It occurs when bacteria which were previously susceptible become resistant after exposure to certain antibiotic
Example about Intrinsic resistance
Ex. Intrinsic resistance to Gram-negative bacteria is thought to be
associated with the outer cell membrane, preventing certain antibiotics
from reaching their intracellular targets
Differences between Intrinsic and Extrinsic?
Intrinsic resistance is always chromosomally mediated
Acquired resistance may occur by mutations in the chromosome or by the acquisition of genes coding for resistance from an external source normally via a Plasmid or Transposon
give me type of bacteria that have Natural (Inherent) Resistance
(non-genetic natural resistant to AMA )
- Mycoplasmas
- Sporulated bacteria
- Tuberculosis
- Spheroplasts and protoplasts
Genetic basis of acquired resistance , there are three genetic elements are responsible for acquired resistance:
- Chromosomal mutations
- Plasmids
- Transposons
Chromosomal mutations could result in development of antibiotic resistance in genes due to changes
in the DNA sequence (point or frame shift)
M. tuberculosis where a minority population of organisms are resistant to which antibiotic ?
isoniazid
and eventually result in overgrowth by this subpopulation of resistant organisms.
Plasmid
Extrachromosomal piece of DNA codes for a number of properties including antibiotic resistance
Transposons
They are jumping genetic elements capable of transferring or transposing independently from one DNA molecule (chromosomes or plasmids) to another
True or False
The central region of the transposon often codes for antibiotic resistance genes.
ترو طبعاً
Mechanisms of Acquired Resistance
1- Reduction in cellular permeability to the antibiotic
2- Production of drug-inactivating enzymes.
3. Efflux Pump
4- Change in the antibiotic target site
5- Switch to alternative metabolic pathways unaffected by the drug.
6-Increased production of essential metabolite: that out compete antibiotic (e.g. increased production of PABA confers
resistance to sulfonamides).
Note: PABA is para-aminobenzoic acid that is used in DHF synthesis
Types of Cells Reduction of cellular permeability
1.Alteration of porins
affect antibiotics uptake e.g. chloramphenicol and cephaloridine
2.Antagonist of Ab-transport process
e.g. tetracyclines and erythromycin (decreasing influx or increasing efflux)
3.Loss of transport process
alanine transport system in case of cycloserine
4.Absence of transport system
aminoglycosides Abs and anaerobes (O2 transport system).
Types of Production of Drug-inactivating Enzymes
- b-lactamases: convert penicillins and cephalpsporins into toxic penicilloic and cephalosporic acids.
- Cross-resistance often occur
معلومة .
b-lactamases are inducible (G +ve) and constitutive (G –ve) enzymes
.