Antimicrobial chemotherapy- antibiotic resistance Flashcards
When is an organism considered resistant?
An organism is considered resistant to a given drug when it is unlikely to respond to attainable levels of that drug in tissues.
What strain is resistant to aminoglycosides?
streptococci
Why are gram negative organisms always resistant to Vancomycin?
Gram-negative organisms
always resistant to Vancomycin
(this is usually due to inability of the drug
to penetrate the bacterial cell wall to exert its action).
What is inherent or intrinsic resistance?
naturally resistant to an antibiotic
What test is required when dealing with acquired resistance?
laboratory sensitivity testing
Describe selective pressure?
because of the huge pressures we put on top of the bacteria- we have facilitated the bacteria to develop specific mutation (particularly toward action of antibiotics)
Describe spontaneous mutation?
change in structure or function which no longer allows the antibiotic to act
Describe spread of resistance?
the gene/s that code for resistance can spread from organism to organism or from species to species.
Genes can be carried on plasmids (extra chromosomal packages of DNA)
or on transposons (packets of DNA which insert themselves into the chromosome).
What are the different types of horizontal transfer?
Conjugation: method of horizontal gene transfer where direct cell-to-cell contact facilitates the exchange of genetic material. This process is primarily mediated by plasmids, small, circular DNA molecules independent of chromosomal DNA.
Transformation: Transformation involves the uptake of naked DNA from the environment by bacterial cells, allowing bacteria to acquire genetic material without direct contact with other organisms.
Transduction: Transduction involves bacteriophages, viruses that specifically infect bacteria. Unlike other modes of gene transfer, transduction relies on these viral intermediaries to facilitate the movement of genetic material between bacterial cells.
What is the most important antibiotic resistance mechanism?
Beta-lactamase production - Beta lactamases are bacterial enzymes which cleave the beta lactam ring of the antibiotic and thus render it inactive
What are the two ways to inhibit the function of the beta lactamase?
1.Through the use of a combination of antibiotics e.g. co-amoxiclav (amoxicillin (a penicillin) plus the beta lactamase inhibitor clavulanic acid)
- take penicillin and make structural changes to make new drug
for e.g. Flucloxacillin - modified penicillin
Which bacteria produce beta lactamase?
most hospital strains of Staphylococcus Aureus produce beta lactamase.
Beta lactamases are also common in gram negative bacilli.
What has been the consequence of extended spectrum beta lactamases?
not able to use most of the beta lactams available, particularly if gram negative.
Why is Carbapenemase-producing Enterobacteriaceae/ carbapenem resistant enterobacteriaceae a clinical problem?
gram negative bacteria, particularly extremely resistant for the carbapenems (beta lactam class of antibiotics).
Describe what happens in the alter
Micro-organisms develop resistance to β–lactams by changing the structure of their Penicillin binding sites
Mutations in PBP genes result in a modified target site to which
β–lactams will no longer bind.
e.g. Methicillin Resistant S.Aureus
