Antibiotics Flashcards
What term is used to describe killing or inhibiting the growth of a microorganism without harming host cells?
selective toxicity
What is the difference between bacteriostatic vs. bactericidal?
bacteriostatic –> inhibit growth (no killing)
bactericidal –> killing
When is bacteriostatic generally used?
when host defenses can be counted on
When is bactericidal generally used?
during infection is severe or patient is immunocompromised
Combination of two antibiotics with enhanced bactercidal activity when used together is known as what?
antibiotic synergism
Combination of antibiotics in which one interferes with the activity of the other is known as what?
antibiotic antagonism
Broad-spectrum antibiotics are effective against a large variety of bacteria, what are the advantages and disadvantages?
advantage: incr. likelihood of effectiveness against a bacterial infection of unknown etiology
disadvantage: incr. likelihood of disrupting the patients normal microbiota (but minor to more serious consequences)
Narrow-spectrum antibiotics are effective against only a small subset of bacteria, what are the advantages and disadvantages?
advantage: avoids disruption of normal microbiota
disadvantage: must have specific disease causing bacteria identified to choose correct antibiotic
True or False. Antibiotics cause resistance
FALSE
What causes antibiotic resistance?
general mutation and/ or acquisition of genetic elements from other bacteria carrying resistance genes
What are the three types of antibiotic resistance?
1) sensitive
2) intermediate
3) resistant
What type of antibiotic resistance could be treated with a recommended dosage regimen of an antimicrobial agent?
sensitive
What type of antibiotic resistance could be treated in body sites where the drug are physiologically concentrated or when a high dosage of drug can be used?
intermediate
What type of antibiotic resistance is not usually inhibited by the usually achieved concentrations of the antimicrobial?
resistant
When is empiric therapy used?
antibiotic treatment while waiting for lab results
When is targeted therapy used?
once lab results have been received and bacteria have been identified
What are some general mechanisms in which bacteria can become antibiotic resistant (5)?
1) breakdown of an antibiotic (hydrolysis)
2) chemical modification of an antibiotic
3) alteration of the target
4) altered permeability, decreased influx or increased efflux
5) lack of target
What are the two types of activity used in antibiotic susceptibility testing?
1) bacteriostatic
2) bactericidal
What is minimum inhibitory concentration (MIC)?
lowest concentration of antibiotic that inhibits growth
What is minimum bactericidal concentration (MBC)?
lowest concentration of antibiotic that kills 99.9%
How is MIC determined?
1) Kirby-Bauer Test (zone of inhibition seen in disk-diffusion assay)
2) E-test (strip of antibiotics with concentration gradient)
How is MBC determined?
broth culture –> check for bacterial growth after overnight incubation
What is targeted in cell wall active vs membrane active antibiotics?
cell wall active –> disrupts peptidoglycan synthesis
membrane active –> disrupts or interferes with membrane integrity/synthesis
True or False. Cell wall active antibiotics are effective against resting and actively dividing bacteria
FALSE. only effective against actively dividing bacteria. it targets the making of PG, if the bacterium is already there, the antibiotics are not effective against it
True of False. Membrane active antibiotics are effective against resting bacteria only
FALSE. they are effective against both resting AND actively dividing bacteria
Are beta-lactams bactericidal or bacteriostatic?
bactericidal
What is the mechanism of action of beta-lactams?
they inhibit cell wall synthesis, specifically they block the active site of transpeptidase
Penicillin is an example of which type of antibiotics?
beta-lactams
What are some ways bacteria become resistant to beta-lactams (4)?
1) altered transpeptidases
2) altered outer-membrane permeability
3) presence of efflux pumps
4) chemical modification of antibiotic
When beta-lactams can no longer bind to the active site of transpeptidase, what kind of resistance have the bacteria undergo?
altered transpeptidases
How does altered outer membrane permeability lead to beta-lactam resistance?
protein channels called porins gain mutations that can cause beta-lactams to no longer gain entrance inside the cell
How does the presence of efflux pumps lead to beta-lactam resistance?
the antibiotics are pumped back out and that effectively reduces the antibiotic concentration within the cell
What’s an example of chemical modification of antibiotic that lead to its resistance?
the bacteria may have beta-lactamase, an enzyme that turns beta-lactams into its inactive form
What is the mechanism of vancomycin?
it recognizes and binds to the 2 D-ala on the end of peptide chains thus preventing transpeptidase from interacting. cross-links can’t be formed = cell death
How can bacteria become resistant to vancomycin?
last D-ala residue has been replaced by a D-lactate and vancomycin can no longer bind to it. cross-links are once again successfully formed and so does cell wall
What antibiotics interferes with dephoshorylation in cyclin of lipid carrier, bactoprenol?
bacitracin
What antibiotics targets protein synthesis?
1) tetracyclines
2) aminoglycosides
3) macrolides
Tetracyclines are bactericidal or bacterostatic?
bacterostatic
Aminoglycosides are bactericidal or bacterostatic?
bactercidal
Macrolides are bactericidal or bacterostatic?
bacteriostatic
What ribosome subunit do tetracylines bind to?
30s
What ribosome subunit do aminoglycosides bind to?
30s
What ribosome subunit do macrolides bind to?
50s
Which of the three protein synthesis inhibitors is generally used as an alternative for individuals with penicillin allergy?
macrolides
Which of the three protein synthesis inhibitors is only effective against aerobic organisms because it is oxygen-dependent?
aminoglycosides
Which of the three protein synthesis inhibitors is a broad spectrum antibiotics?
tetracyclines
What are the three nucleic acid synthesis inhibitors?
1) quinolones
2) rigampin, rifabutin
3) metronidazole
Which of the nucleic acid synthesis inhibitors are bactericidal?
all three are bactericidal
Which of the nucleic acid synthesis inhibitors inhibits DNA replication, recombination and repair?
quinolones
Which of the nucleic acid synthesis inhibitors binds to DNA-dependent RNA polymerase and inhibits initiation of RNA synthesis?
rifampin, rifabutin
Which of the nucleic acid synthesis inhibitors gets reduced bacteria and becomes toxic that damages their DNA?
metronidazole
What type of antibiotics is sulfonamides and trimethoprim?
antimetabolites
What is the mode of action for sulfonamides and trimethoprim?
they target folate metabolism thus preventing bacteria from having the necessary material to build DNA and RNA
