Ch. 15 Antimicrobial Drugs Flashcards
(25 cards)
Bacteriostatic drugs
cause a reversible inhibition of growth, with bacterial growth restarting after elimination of the drug
Bactericidal drugs & who specifically needs it
kill their target bacteria; necessary for life-threatening infections
- immunocompromised patients
what does spectrum of activity of an antibacterial drug relate to
diversity of targeted bacteria
Narrow-spectrum drugs
if the pathogen causing an infection has been identified, best use narrow-spectrum antimicrobial and minimize collateral damage to the normal microbiota
- some only target gram-positive bacteria while others only target gram-negative
Broad-spectrum antimicrobial
targets a wide variety of bacterial pathogens; frequently used as an empiric therapy to cover a wide range of potential pathogens while waiting on the lab identification of the infecting pathogen
- both gram-positive and gram-negative species
- also used for polymicrobial infections
- used when a narrow-spectrum drug fails
Risk associated with broad-spectrum antimicrobials
also target a broad spectrum of the normal microbiota –> increase risk for secondary infection (superinfection)
superinfection
develops when the antibacterial intended for the preexisiting infection kills the protective microbiota
antibiotics (chemotherapeutic drugs) are specific to what domain
antibacterial aka. bacterium – target bacterial processes if process is vital for bacterial growth
- bacteria do process different from host
- does not harm human host
- safe to use in human body
Selective toxicity
antimicrobial drug selectively kills or inhibits the growth of microbial targets while causing minimal or no harm to the host
basis of antibiotic function
the diversity of 70S ribosomes reinforces the fact that each antibiotic is a tiny molecule that fits into one site in a catalyst to block its activity
What makes development of drugs against viruses difficult?
- viral simple structure
- obligate intracellular pathogens – use host’s cellular machinery to replicate
Most antiviral drugs are nucleoside analogs and function by…
inhibiting nucleic acid biosynthesis
Ways viruses function: just think about, don’t memorize
- inhibiting nucleic acid biosynthesis ex) acyclovir
- interfering with both DNA and RNA synthesis, perhaps by reducing GTP ex) Ribavirin
- binding to transmembrane protein ex) amantadine
- neuraminidase inhibitors ex) taminflu
- biding to the viral capsid ex) pleconaril
- combinations of synthetic antiviral drugs
Why aren’t there “broad spectrum” antivirals?
Viruses lack metabolic pathways, viruses use a hosts ribosomes and polymerases
- viruses offer few conserved vulnerabilities (like 70S ribosome for instance)
If an antiviral drug blocked translation or transcription, what would happen?
The host would be devastated
How do bacteria fight back against antibiotics?
-Target modification: antibiotic targets can spontaneously mutate, the mutated form still does its catalytic job but it doesn’t fit the antibiotic as well
- New genes: gained to execute even greater levels of antibiotic resistance
Four mechanisms for antibiotic resistance
1) Efflux pumps
2) Blocked penetration
3) Inactivation of enzymes
4) Target Modification
Efflux pumps
use bacterial cell energy to push antibiotics out of the bacterium through an exporter protein
- prevents accumulation of drug to a level that would be antibacterial
- prevents drug from reaching its target
Blocked penetration
bring in a NEW, antibiotic resistant form of the target; target replacement or inactivation through hydrolysis
Target modification
structural changes to antibacterial drug targets can prevent binding –> drug is ineffective
- occurs through spontaneous mutation – evolutionary advantage to develop drug resistance
Inactivation of enzymes
degradative enzymes: enzyme attacks the antibiotic and breaks it down
What carries efflux pumps, antibiotic degradative enzymes, and target replacement?
Bacterial genes: transposons
-transposons carry an antibiotic resistance gene alongside their transposase gene
How does a transposon move, enter a cell, and pass to future generations?
plasmid with transposon enters cell via HGT –> generations later, transposon may hop to a chromosome –> random transposition events may occur –> over time, HGT events spread plasmids and chromosomal fragments to unrelated bacteria
What happens when an antibiotic is present in an environment where only one cell is resistant?
Selection for antibiotic resistance
-future generations will have resistance as a result
