CHAPTER 10 Flashcards
What are drugs?
chemicals that affect physiology in any manner
What are chemotherapeutic agents?
drugs that act against disease
What are the modes of action of antimicrobials?
inhibition of cell wall synthesis,
block a pathogens attachment to host,
inhibition of protein synthesis,
breakdown of the cell membrane structure or function,
interference with functions of DNA and RNA,
blockage of key metabolic pathways
What are the major action modes of antibacterial drugs?
inhibition of cell wall synthesis- ex. penicillins;
inhibition of protein synthesis- ex. tetracyclines;
inhibition of nucleic acid replication and transcription- ex. quinolones;
injury to plasma membrane- ex. polymyxin B;
inhibition of essential metabolite synthesis- ex. sulfanilamide
What mode of action has no affect on the existing peptidoglycan layer and only is effective for growing cells?
inhibition of synthesis (on bacterial cell walls)
Major drugs targeting bacteria?
isoniazid, polymycin, penicillin, streptomycin, erythromycin, tertracycline, sulfonamides
Major drugs targeting fungi?
echinocandins, nystatin, amphotericin B, azoles, allylamines
Major drugs targeting vegetative cells?
.
Major drugs targeting spores?
.
Major drugs targeting protozoa?
atovaquone, azoles
Major drugs targeting helminths?
niclosamide, praziquantel
Major drugs targeting viruses?
arildone, ribavirin, acyclovir
What makes viruses the trickiest targets?
the virus has to attach to host cell, then enter the cell, then uncode its genetic information, and then attack and take over cell. Several processes need to be interfered with which makes it more difficult to target
How do we measure resistance?
take sample and put in agar or broth, expose to various drugs and observe if they divide and thrive or not
How do we measure effectiveness of a drug?
diffusion susceptibility test, minimum inhibitory concentration test, minimum bactericidal concentration test
Why do we need to be careful with antibiotics?
drug toxicity can occur; drugs can be toxic to kidneys, liver, or nerves; need to specifically consider drugs for pregnant women carefully
What can go wrong with antibiotics?
allergies, disruption of normal microbiota (causing secondary infections),
How can we combat resistance?
maintain high concentration of drug in patient for sufficient time;
use antimicrobial agents in combination (synergism and antagonism)
What are the mechanisms of resistance?
blocking entry,
inactivation by enzymes,
alteration of target molecule,
efflux of antibiotic
What is synergism?
occurs when one drug enhances the effect of a second drug
What is antagonism?
occurs when drugs interfere with each other
What is antagonism?
occurs when drugs interfere with each other
What are 7 ways microorganisms can be resistant to antimicrobial drugs?
• produce enzyme that destroys or deactivates Slow or prevent entry of drug into the cell
• Alter target of drug so it binds less effectively
• Alter their own metabolic chemistry
• Pump antimicrobial drug out of the cell before it can
act
• Bacteria in biofilms can resist antimicrobials
• Mycobacterium tuberculosis produces MfpA protein
What is horizontal gene transfer?
genes transferring from one bacteria to the other
What are the ways R plasmids can be acquired in drug resistance?
transformation, transduction, conjugation
What is transformation?
transfer of free DNA
What is transduction?
transfer by viral delivery
What is conjugation?
plasma transfer
Inactivation of drug example
penicillin by beta-lactamase, an enzyme that cleaves a portion of the molecule and renders it inactive
decreased permeability
receptor that transports the drug is altered, so the drug cannot enter the cell
activation of drug pumps
specialized membrane proteins are activated and continually pump the drug out of the cell (efflux pumps)
change in drug binding site
binding site on target (ribosome) is altered so drug has no effect
use of alternate metabolic pathway
the drug has blocked the usual metabolic pathway so the microbe circumvents it by using an alternate, unblocked pathway that achieves the required outcome
