Biology Chapter 8

what is a drug?
anything that effects the physiology of an organism
ex: caffeine, alcohol, nicotine
what are chemotherapeutics?
drugs that act against a disease
ex: lipatpor, nexium, humira
what are antimicrobial agents?
drugs that treat an infection by either killing or slowing the growth of a microbe
why is Paul Ehrlich important?
coined the term chemotherapy to describe compounds that would selectively kill pathogens
(magic bullets)
why is Gerhard Domagk important?
chemist who discovered sulfanilamide (Prontosil) — Prontosil was the first commercially available antibiotic — Gerhard was jailed because he acknowledged he won the Nobel Prize
why is Alexander Fleming important?
discovered Penicillin released from penicillium (fungi) can kill bacteria — left plates by window sill and penicillin blew in and bacteria wouldn’t grow around it
why is Selmen Waksman important?
found that antibacterial compounds are made by other bacteria — coined the term antibiotics, found that streptomyces was effective against streptomycin
what are antibiotics?
compounds made by microorganisms that kill other microorganisms
what are semisynthetics?
chemically altered antibiotics that are more effective than naturally occurring ones
what are synthetics?
antimicrobials that are completely synthesized in a lab
Selective Toxicity
key to any antimicrobial being effective — compounds that kill the microbe but not the host
what is the most common way to prevent bacterial cell wall synthesis?
prevent cross linkage of NAM subunits by using Beta-Lactam rings to bind to enzymes that cross-link NAM subunits
what are beta-lactams effective against?
gram positive bacteria because of the their thick peptidoglycan cell walls
What Beta-Lactams interfere with bridges that link NAM subunits in many Gram Positives?
Vancomycin and Clycloserine
What Beta-Lactam blocks secretion of NAG and NAM from cytoplasm?
Bacitracin
What Beta-Lactam disrupts mycolic acid formation in mycobacterial species (effective against TB if resistant against Streptomycin)?
Isoniazid and Ethambutol
Drugs that prevent bacteria from increasing amount of Peptidoglycan?
Vancomycin and Clycloserine
Bacitracin
Isoniazid and Ethambutol
Function of Echinocandins?
disrupt fungal cell wall biogenesis
Function of Caspofungin?
inhibits enzymes that produce glucan
Glucan = essential for fungal cell wall biosynthesis
What do fungi cytoplasmic membranes contain?
Ergosterol
What do human cytoplasmic membranes contain?
Cholesterol
What is the function of Amphotericin B?
attaches to ergosterol in fungal membranes (inhibits ergosterol by using Amp B)
What infection does Amp B treat?
can be used orally for thrush which is a fungal infection in the mouth
CANNOT be used on bacterial infections
Bacteria lack sterols: not susceptible
Function of Aminoglycosides for inhibition of protein synthesis?
(Streptomycin) causes change in 30S shape so mRNA is misread
Function of Tetracycline for inhibition of protein synthesis?
Tetracycline and some aminoglycosides block docking site of tRNA
Prevents insertion of amino acids in the growing peptide chain
Function of Chloramphenicol for inhibition of protein synthesis?
blocks peptide bond formation
cheap & easy to produce — side effects no longer make it the first choice drug that it once was
Function of Lincosamides or macrolides for inhibition of protein synthesis?
bind 50S subunit which blocks proper mRNA movement through ribosome — synthesis stops
Function of Antisense for inhibition of protein synthesis?
insertion of nucleic acid
What is AZT used for?
a nucleotide analog used to treat viral infections by inhibiting reverse transcriptase
What virus is reverse transcriptase necessary for?
HIV and other viruses
Function of Rifampicin
binds to RNA polymerase at a site adjacent to the RNA polymerase active center and blocks RNA synthesis by physically blocking the formation of the phosphodiester bond in the RNA backbone (blocks mRNA & proteins)
What do Quinolones do?
interfere with the metabolism of malaria parasites
What makes an ideal antimicrobial?
Readily available
Inexpensive
Chemically stable
Easily administered
Non toxic and Non Allergenic
What is the spectrum of action?
the number of different pathogens a drug acts against
Narrow-Spectrum
effective against few organism
Broad-Spectrum
effective against many organism
-may allow for secondary or superinfections to develop
-killing of normal flora reduces microbial antagonism
Diffusion Test
paper circle placed in bacterial lawn and if bacteria does not grow around it then it is a good antibiotic (zone of inhibition = where bacteria doesn’t grow)
Minimum inhibitory concentration test
the lack of turbidity in a test tube inhibits growth
Minimum bactericidal concentration test
allows one to determine the concentration of a drug that it takes to kill a microbe (bacteriocidal/fungicidal) activity
Tropical application of drug
for external infections
Oral route
requires no needles and is self-administered
Intramuscular administration
delivers drug via needle into muscle
Intravenous administration
delivers drug via needle to bloodstream
Toxicity
-cause of many adverse reactions
-drugs may be toxic to kidneys, liver, or nerves
-consideration needed when prescribing drugs to pregnant women
Allergies
-allergic reactions are rare but can be life threatening
-immune system response
-anaphylactic shock
Effects of disruption of normal microbiota by antibiotics
-may result in secondary infections
-overgrowth of normal flora causes superinfections
-greatest concern for hospitalized patients
T/F all resistance is caused by mutation
False: some pathogens are naturally resistant
Which two ways is resistance by bacteria acquired?
-New mutations of chromosomal genes
-Acquisition of R-plasmids via transformation, transduction, and conjugation
What are the 7 known mechanisms of microbial resistance to antibiotics?
-Produce enzymes that destroys or deactivates drug
-Slow or prevent entry of drug into the cell
-Alter target of drug so it binds less effectively
-Alter their metabolic chemistry
-Pump antimicrobial drugs out of the cell before it can act
-Biofilms retard drug diffusion and slow metabolic rate
-Myobacterium TB produces MfpA protein
What does the protein MfpA do?
binds to gyrate and blocks fluoroquinolone from binding
What is a superbug?
a microbe that is resistant to three or more classes of antibiotics
What is Cross resistance?
a phenomena of one antibiotic resistance mechanism leading to resistance to other similar antibiotics
Synergism
antibiotics that work together
Antagonism
antibiotics that work against each other
ex: penicillin is going to be problematic to the cell wall (not being synthesized) only will hurt if bacteria is continuing to grow, if you’re going to give penicillin and another drug to slow growth it will not be beneficial
Orphan Drug Development
provides orphan status to drugs and biologics which are defined as those intended for the safe and effective treatment, diagnosis or presentation of rare diseases that affect fewer than 200k people in the US
What are 5 methods of limiting resistance?
Maintain high concentration of drug in patient for sufficient time (kills all sensitive cells and inhibits others so immune system can destroy them)
Use antimicrobial agent in combination (synergism vs antagonism)
Use antimicrobials only when absolutely necessary
Develop new variations of existing drugs
Search for new antibiotics, semisynthetics, and synthetics
why is penicillin regarded as the first true antibiotic?
It is produce naturally by the fungus Penicillium
What is microbial antagonism?
the ability of the normal flora to outcompete and outgrow pathogens
what is a superinfection?
A disease caused by an organism that is often an opportunist or one that was present in low numbers — a sequel to removal of the normal flora by antibiotic treatment
What causes thrush?
candida albicans
Which of the following classifications would best describe Candida Albicans?
yeast
What is meant by selective toxicity?
Chemotherapeutic agents should act against the pathogen and not the host
Why are chemotherapeutic agents that work on the peptidoglycan cell wall of bacteria a good choice of drug?
Humans and other animal hosts lack peptidoglycan cell walls
Quinolones and Fluoroquinolones act against what bacterial target?
DNA gyrase
Why is it difficult to find good chemotherapeutic agents against viruses?
Viruses depend on the host cell’s machinery, so it is hard to find a viral target that would leave the host cell unaffected
_____ cells would be expected to be the most susceptible to the action of polyene drugs such as amphotericin B, while ______ cells would be the least susceptible.
fungal; bacterial
Why is the drug actinomycin used only in research applications or in the treatment of cancer?
because it is active against both prokaryotic and eukaryotic cells
Which of the following is NOT a direct mode of action of antimicrobial drugs?
inhibition of flagella formation
An antimicrobial drug that blocks the transport of NAG and NAM from the cytoplasm is targeting which of the following cellular processes?
cell wall synthesis
Why do antimicrobial agents active against mycobacteria have to be administered for months or years rather than the typical 10-30 days prescribed to treat other infections?
Mycobacteria reproduce very slowly
Which of the following antimicrobial drugs would likely be useful to treat a staphylococcal infection?
erythromycin
Oxazolidinones
block initiation
Aminoglycosides
change 30S subunit
Antisense nucleic acids
block ribosome attachment
Lincosamides and Macrolides
block ribosome movement
Tetracyclines
block tRNA docking
Chloramphenicol
inhibits peptide bonding
Which of the following is NOT a type of side effect exhibited by antimicrobial drugs?
inhibition of host cellular enzymes
An antimicrobial disks on Kirby-Bauer plate that shows no zone of inhibition indicates that the microbe being tested is ______ to the drug
Resistant
Which antibiotic is overcome by beta-lactamases?
Penicillin
How might efflux pumps increase antibiotic resistance in bacteria?
Resistant bacteria can have more efflux pumps, and can have less specific efflux pumps
The process of acquiring antibiotic resistance by means of bacteriophage activity is called _____
R-plasmid acquisition
Which of the following mutations would not result in antibiotic resistance?
Silent Mutation
R-plasmids are most likely acquired via ______
bacterial conjugation
Which of the following activities can be shown to increase resistance among microbial populations?
taking antibacterial drugs for viral infections
If a particular bacterial species is resistant to beta-lactam antibiotics, which of the following might you expect to find inside the bacterial cells?
R-plasmids
Which of the following is NOT associated with microbial mechanisms of resistance?
denaturation of proteins

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