Ch. 13 Flashcards
What is the goal of antimicrobial chemotherapy?
To administer a drug to an infected person that destroys the infective agent without harming the host’s cells
Common metabolic products of bacteria and fungi.
Antibiotics
How are semisynthetic drugs created?
By chemically altering the structure of naturally occurring antibiotics
Why are synthetic drugs used?
Because you can’t get some natural compounds without destroying a habitat or population so drugs created in a lab mimic the action of natural compounds
Central concept in antibiotic treatment; antimicrobial drugs should kill or inhibit microbial cells without simultaneously damaging host tissues.
Selective toxicity
The best drugs block actions of molecules in microorganisms but not ___ cells.
Vertebrate cells
Name a drug with excellent selective toxicity
Penicillins because they block the synthesis of the cell wall found only in bacteria
What characteristics make a drug most toxic to human cells?
Drugs that act upon a structure common to both the infective agent and the host cell
When does selective toxicity become more difficult?
As the characteristics of the infectious agent become more similar to that of the host
What are the metabolic targets of chemotherapeutic agents?
Inhibition of: cell wall synthesis, nucleic acid (DNA/RNA) structure/function, protein synthesis, folic acid synthesis
Interference with: cell membrane structure/function
Drugs that are affective against more than one group of bacteria. Give an example.
Broad spectrum drugs. Example: tetracyclines
Drugs that only target a specific group. Give an example.
Narrow spectrum drugs. Example: polymyxin and penicillins
Drugs that target protein synthesis. Broad spectrum. What are the side effects?
Tetracyclines. Side effects include gastrointestinal disruption and deposition in hard tissues
Drugs that target folic acid synthesis. First modern antimicrobial drugs. Synthetic.
Sulfonamides or sulfa drugs
What do Biofilms do?
Interrupt quorum sensing pathways and add DNAse to antibiotics; pretreatment
What is quinine?
An antimalarial drug that was the principal treatment for hundreds of years. Replaced by less toxic chloroquine and primaquine
What are protozoan infections?
Parasitic diseases
An antibiotic used as chemotherapy for other protozoan infections
Metronidazole (an amoebicide)
What are the three major modes of action for antiviral chemotherapeutic agents?
1) Barring penetration of virus into host cell
2) Blocking transcription and translation of viral molecules
3) Preventing maturation of viral particles
Adaptive response in which microorganisms begin to tolerate an amount of drug that would ordinarily be inhibitory
Drug resistance
Bacteria must be resistant to any antibiotic that they themselves produce
Intrinsic resistance
Bacterial resistance to a drug which they were previously sensitive
Acquired resistance
What are three ways drug resistance can develop?
1) resistance through spontaneous mutation
2) resistance through horizontal transfer
3) sharing of resistance genes accounts for the rapid proliferation of drug-resistant species
Plasmids that are transferred through conjugation, transformation, or transduction
Resistance (R) factors (resistance through horizontal transfer
The ratio of the dose of the drug that is toxic to humans to its minimum effective dose (closer two figures are to each other greater potential for toxic drug reactions)
Therapeutic index (TI)
Smallest concentration of drug that visibly inhibits growth. Helps determine smallest effective dose.
Minimum inhibitory concentration (MIC)
If treatment fails, what are some possible reasons why?
Inability of drug to diffuse into body compartment; resistant microbes in infection that don’t make it into sample collected for testing; infection caused by more than one pathogen mixed, some of which are resistant to the drug
Explain the livestock bacteria situation
Enteric (intestinal) bacteria share resistance plasmids that are constantly selected and amplified by exposure to drugs. These pathogens jump to humans and cause drug-resistant infections
What is the novel approach to antimicrobial therapy?
Disabling host molecules that the invaders use to enhance their position
Why is phage a low tech solution?
Extremely specific and only infect one species of bacteria, leaving normal microbiota alone
Preparations of live microorganisms fed to animals and humans to improve intestinal biota. Replace microbes lost during antimicrobial therapy. Help the biota already there.
Probiotics (ex: probiotic yogurt)
Nutrients that encourage growth of beneficial microbes in the intestine
Prebiotics.
Example of a prebiotic; encourage growth of bifidobacterium in the large intestine and discourage the growth of pathogens; a polymer of fructose molecules and occur in agave, artichokes,wheat, onions, etc.
Fructans
Bind to the enamel of teeth and turn gray/brown. Cause liver damage in pregnant women. Cross the placenta and are deposited in fetal bones and teeth
Tetracyclines
