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Microbiology Antibiotics Antiviral Chemotherapeutic
Micro lecture exam 3
EZ book and notes
How did Paul Ehrlich first help discover the use of selective toxicity using dyes for microscopy?
He noticed that some dyes during staining would stain microbes but NOT animal cells.
He thought that the dyes that stuck to the components of microbial cells could inhibit microbial growth, plus only effect prokaryotes and not animal cells.
These drugs were the first to be found effective against a wide range of bacteria, discovered by Gerhard Dogmagk at the Bayer Chemical Co.
What did Alexander Flemming help discover and how did he do this?
: When he noticed unusual growth pattern on some of the plates of growing bacteria in his lab, which was contaminated by mold.
Around the mold, there was a clear zone which contained no growing bacteria.
The clear zone was from the fungus secreting a chemicl that inhibited the growth of bacteria.
This term means the ability to poison a microbe, but not harm the host.
Why are fungi and viruses hard to treat with antimicrobial drugs?
Fungi and parasitic worms are Eukaryotic pathogens that have similiar cell structures to human cells. It's hard to find the selecive toxicity.
Viruses use human cells to reproduce and have very few characteristics to target with drugs.
If a drug had a therapeutic index of 100mg/1mg per cubic cm., would it be safe to take? Why or why not?
100mg <--Toxic Dose
1mg <--Therapeutic Dose
A 100mg toxic dose means a 100 mg of the drug must be consumed before it harmed the host.
However, as little as 1mg is enough to have beneficial results before it ever reaches the toxic dose.
What is the term for a drug when it inhibits the growth of both gram-positive and gram-negative bacteria?
Broad spectrum drug
What is the class of drug referred to when it is only effective against gram-positive bacteria for example?
What are the possible ways that antimicrobial drugs can inhibit bacterial growth? (4 Listed)
1. Inhibit protein synthesis
2. Inhibit Cell wall synthesis
3. Inhibit mRNA synthesis
4. Inhibit DNA synthesis
What is the mechanism of action of sulfa drugs? Why does it not effect human cells?
They inhibit bacterial growth by interfering with an important metabolic pathway that synthesizes folic acid.
It does this by inhibiting the activity of an important enzyme.
Folic acid is important for the synthesis of DNA
Host is not affected because humans get their folic acid from food, and do not need to make their own.
What is the mechanism of action of penicillin drugs?
Inhibit the formation of the peptidoglycan in bacterial cell walls.
How can inhibition of protein synthesis harm bacterial cells but not human cells when the target are ribosomes and both cell types have this structure?
Prokaryotic ribosomes are smaller and have slightly different protein and rRNA components than those of eukaryotic ribosomes.
However, mitochondria inside eukaryotic cells have and there are side effects due to their similiar size to prokaryotic ribosomes.
T or F: Antimicrobial drugs that disrupt the plasma membrane of bacteria have a low selective toxicity.
: Prok. And Euk. Plasma membranes are similiar.
An antifungal disrupts bacterial membranes by binding to the sterols that are found on fungl membranes and lysing the cell.
Explain why inhibition of nucleic acid synthesis is difficult to make and how it can be overcome.
There are similarities in acid synthesis in bacterial and eukaryotic cells.
All cells have DNA and RNA, and their respective polymerases.
There are differences though with the enzymes used in bacterial and human cells.
For example, bacteria have DNA gyrase, which is required for the coiling of bacterial DNA. This is then targeted by drugs since human cells to not have this enzyme.
What is apoptosis and how does it occur? How does it occur using antimicrobial drugs?
Apoptosis is a programmed cell death. It occurs when a cell is damaged or ages.
Some antibiotics trigger apoptosis in bacteria by activating proteins called autolysins that dissolve the cell wall during apoptosis.
How does the antiviral drug, AZT, inhibit viral growth? Is it selectively toxic?
It mimics the nucleotide, thymine.
It is inserted into the growing DNA strand, into the active site of DNA polymerase.
Because their chemical structure is not actually that of nucleotides, no more nucleotides cn be added to the chain, and replication is stopped.
Viral reverse transcriptase has a higher affinity for AZT than human DNA polymerse, so it is selectively toxic.
Tamiflu is an antiviral drug tht inhibits the enzyme, neuraminidase, located on the surface of the flu virus.
What does the enzyme do and how does the drug inhibit this virus?
Antiflu drugs act as neuraminidase inhibitors.
Neuraminidase is essential in the release of the virus from the infected cell.
The drug blocks the making of this protein, which stops viral replication, and shortens the flu symptoms (if taken very soon after exposure)
How do protease inhibitors work to treat HIV?
Protease is a viral enzyme that is needed to cut viral proteins during maturation of the virus.
Thus, the drug prevent completion of the viral replication cycle.
How have interferons been used in recombinant DNA technology and why?
Interferons re cytokines that are made by virally infected cells and signaling neighboring cells to protect themselves against viral attack.
After producing high levels of interferons from recomb. DNA tech, they have been used to treat hepatitis, influenza, and herpes infections.
What is the purpose of the Kirby-Bauer test? How is this done?
It is to determine the spectrum of activity of an antimicrobial drug.
Paper disks that contain different concentrations of antibiotics are observed for clear zones, which indicates a positive inhibition of bacterial growth with that antibiotic.
When determining the proper dose of an antimicrobial drug, what is the name of the lowest concentration of the drug that inhibits growth?
Minimum Inhibitory concentration (MIC)
What are the two main types of drug resistant microbes?
1. Inherent resistance
2. Acquire Resistance