Exam 1 - (3) Antibiotics Flashcards
Who discovered Penecillin in 1920?
Alexander Fleming
What WWII heroes (1940) demonstrated the safety and effectiveness of penicillins in humans?
-Ernst Chain, Howard Flory
What are the two modes of antibiotic action?
- Bactericidal
- Bacteriostatic
What is the difference between bactericidal and bacteriostatic antibiotics?
-Bacteriostatic slow down bacterial replication/halt growth, bactericidal kill bacteria.
What are some qualifications of the “ideal” antibiotic?
- Broad spectrum of activity
- Would not induce bacterial resistance
- High therapeutic index (highly potent but non-toxic to patient; therapeutic index is toxic dose:effective dose)
- Selective toxicity (specific microbes targeted, not host cells)
What are some ways an antibiotic achieves selective toxicity?
Targets structures that are unique in microbes:
- cell wall
- enzymes (replication, transcription, translation)
- metabolities
- Ribosome structure
What are the five ways antibiotics inhibit bacteria?
1- Inhibition of cell wall synthesis 2-Disruption of cell wall function 3-Inhibition of protein synthesis 4-Inhibition od nucleic acid synthesis 5-Action as antimetabolites
What are some examples of antibiotic cell wall synthesis inhibition?
- prevent NAG-NAM binding in the cytoplasm
- prevent peptide side chain binding
- prevent linking of side chain units
- prevents cross-linking of chains
Penecillin disrupts cell wall synthesis, how?
-causes competition for bacterial enzyme that cleaves D-ala - D-ala linkage in cell wall synthesis, enzyme instead cleaves penicillin creating toxic fragments.
What do generations of antibiotics related to penicillin have in common?
a beta-Lactam ring within their structure
Polymyxin B sulfate is an example of an antibiotic which operates by disrupting bacterial cell membranes, how?
It binds to membrane phospholipids.
-note: Polymyxin B sulfate is toxic to eukaryotic cell membranes as well, and as a result is applied topically.
Antibiotics that operate by inhibiting protein synthesis act on which bacterial cycle/structure
Ribosome (which is “different” than eukaryotic ribosome)
What are some antibiotics that disrupt the bacterial ribosomal cycle?
- Linezolid
- Tetracycline
- Aminoglycosides
- Macrolidies, choramphenicol
One mode of antibiotic action is inhibition of nucleic acid synthesis. However, many inhibitors bind to ______ and are thus too ______ for use.
- DNA
- toxic
Metronidazole is an exception to the toxic DNA binding inhibitors. This is because it is ______ until it is converted to it’s ______ form by ______ microbes. Therefore it is only active in ^this type^ of bacteria.
- inert
- active
- anerobic
Nalidixic acid and Quinolones are examples of antibiotics that affect which bacterial replication structure?
DNA gyrase
Rifamycin is an antibiotic that inhibits which bacterial replication structure?
RNA polymerase
Para-aminobenzoic acid (PABA) and Para-aminosialic acid are bacteriostatic antibiotics which operate as:
Antimetabolites
A result of antibiotic overuse (Agricultural use, Physician misuse, Pharmacist misuse, patient misuse) is:
antibiotic resistance within the bacteria they target.
What are the three steps in the action of antibiotics on which drug resistance can act?
1- Drug penetrates the envelope
2-Transport into the cell
3-Drug binds to the target
What are three mechanisms of drug resistance?
1-Synthesis of enzymes that inactivate the drug
2-Prevention of access to the target site
-Inhibiting uptake
-Increasing secretion of the drug
3-Modification of the target site
Penicillin is deactivated by resistant bacteria by:
synthesizing enzymes which break a bond in penicillin’s b-lactam ring
Drug resistant bacteria can prevent the uptake of antibiotics by
- blocking porins to the antibiotics
- creating drug efflux pumps to pump antibiotics out of them (all classes of bacteria have these to some degree)
Bacteria can render antibiotics useless by modifying their target sites. Two ways of accomplishing this are:
- Modifying enzyme activity (e.g. developing a higher affinity for a molecule other than the antibiotic)
- Altering their metabolic pathways
Name three ways antibiotic resistance spreads:
1-Chromasome associated resistance
2-Plasmid mediated resistance
3-Rapid spread of resistance
Bacterial sensitivity to antibiotics occurs over a ______ range.
Dynamic (the few bacteria that are resistant to the antibiotic will eventually thrive and can spread)
How do you combat an antibiotic resistant pathogen?
- Synergism - penecillin and streptomycin
- Antagonism - chloramphenicol and penecillin
- Indifference
What are drawbacks to administering an antibiotic cocktail?
- Failure to eliminate pathogen (increased likelihood of superinfection)
- Synergistic Toxicity
Are antibiotics effective against all microbes?
NO!!!! (fungi, viruses)
