S4L1 - Antibiotics And Resistance Flashcards
(38 cards)
What are the 4 main classes of antimicrobials?
Antibacterial, antifungal, antiviral and antiprotozoal agents
What is the difference between bactericidal and bacteriostatic?
Bacteriocidal = capable of killing bacteria
Bacteriostatic = arrest bacteria growth and multiplication.
What are the 4 different mechanisms of action of antibiotics?
Disrupting cell wall synthesis
Disrupting cell membrane function
Inhibiting nuclei acid synthesis
Disrupting protein synthesis
What is the difference between broad and narrow antibiotics? What are their advantages?
Broad spectrum = affect both gram positive and gram negative. Have more side affects as affect non-target microorganisms that may cause side affects.
Narrow spectrum = act against a small spectrum of microorganisms. Are specific to certain bacterium, will not affect many bacterium.
What factors need to be considered when choosing an antiobiotic?
Activity against target organisms Appropriate mode of transmission to reach site of infection Correct formulation (IV/Oral) Dosing frequency/half life Interaction with other drugs Toxicity issues Therapeutic drug monitoring requirements
What 3 mechanisms are used to measure antibiotic activity?
Disc diffusion testing
Broth microdilution
Strip E test
How does disc diffusion testing work?
sample is spread evenly over agar plate. Paper discs are impregnated with different antibiotics and places on the agar. Incubated over night. Measure zone of clearance to see which antimicrobial is most effective. The further the effective the more effective.
What is MIC?
The MIC is the minimum inhibitory concentration. It is the first concentration of the antibiotic that inhibits the growth of the bacteria
What is broth microdilation?
Cultures of different samples of bacterium. Add broth containing antibiotics in increasing doubling concentrations. MIC is concentration of broth added when sample appears clearer/bacterial culture killed.
What is a minimum inhibitory concentration E test?
A strip containing antibiotic at a gradient of concentration. This strip is placed on a contaminated agar plate. Zonal clearing occurs around the strip.
The first number where there is no growth will be the MIC.
Advantage is that is is less time and labour intensive than broth microdilution
What are the 4 different mechanisms of action of antibiotics?
Can affect:
- cell wall synthesis
- cell membrane function
- nuclei could acid synthesis
- protein synthesis
What antibiotics affect cell wall synthesis?
Beta-lactams (penicillins, cephalosporins)
Glycopeptides
What antibiotics affect cell membrane function?
Polymixins
What antibiotics affects the nuclei acid synthesis?
Quinolone
Trimethoprim
Rifampicin
How does penicillin work?
Penicillin reacts with penicillin binding protein, a protein that usually forms the cross linking between the cell membrane and the cell wall. The penicillin stops the formation of cross linking between the cell membrane and the cell wall. This weaken the bacterial wall, allowing influx of water and lysis of the bacterium.
How does vancomycin work?
Vancomycin binds with the nucleic acid chains between the cell wall and the cell membrane. As vancomycin is blinded to these nucleic acid strands, the cell wall cross-linking enzyme cannot attach, and therefore no cross linkages are made. Cell wall is then weakened and lysis occurs.
What are the 3 different types of resistance?
Intrinsic
- no target or access for the drug
- usually permanent
Acquired
- Acquires new genetic material or mutates
- usually permanent
Adaptive
- The organism responds to stress (subinhibitory level of the antibiotic
What are the 3 mechanisms of resistance?
- Enzymatic modification or destruction of antibiotics
- Enzymatic alteration of antibiotic targets
- Mutations of bacterial target sites
How do antibiotics promote chromosomal gene mutation?
When bacteria are exposed to antibiotics, if there is a bacteria present that has a chromosomal gene mutation that provides resistance to the antibiotic then it will not be destroyed by the antibiotic. Only the unmutated bacteria are removed. This leaves the mutated bacterium with less competition, so it can go on the replicate at an increased rate.
What are plasmids?
small circular DNA molecules. Bacteria can pick up new plasmids from other bacterial cells (during conjugation) or from the environment. They can also readily lose them – for instance, when a bacterium divides in two, one of the daughter cells might miss out on getting a plasmid.
Describe horizontal gene transfer
One bacterium can transfer plasmids to another recipient bacterium. They can be bacterium of different species. This allows different genes and therefore properties to be transferred from one species of bacteria to another, such as resistance.
What are commonly used Beta-lactams?
Penicillins
Cephalosporins
Carbapenems
Monobactams
What are the main functions of penicillin?
Penicillin
-Narrow spectrum. Effective against Streptococci.
Amoxicillin
- also some activity against gram negative
Flucloxacillin
- active against staphylococci and streptococci
What are B-lactamase inhibitor combinations?
Combinations of penicillins and beta-lactamase inhibitors.
Used to treat UTI’s
Co-amoxiclav
Piperacillin
