Lecture 13 [Exam 3] Flashcards
What played a major role in life expectancy?
Antibiotics
50%–60% of hospital-acquired (nosocomial) staphylococcus
infections are caused by _______________.
methicillin-resistant S. aureus (MRSA)
___________ are compounds produced by one species of microbe that can kill or inhibit the growth of other microbes.
Antibiotics
True or False: Antibiotics also includes synthetic chemotherapeutic agents (useful clinically but synthesized chemically)
True
What began the modern antibiotic revolution?
Penicillin
Who discovered penicillin?
Alexander Fleming
True or False: Penicillin originates from Penicillium notatum.
True
What two scientists purified penicillin?
Howard Florey & Ernst Chain
__________ are inactive until converted by body to
active agents, sulfanilamide.
sulfa drugs
Who discovered sulfa drugs?
Gerhard Domagk
___________ is a precursor of folic acid, a vitamin needed
for DNA synthesis
Analogs of para-aminobenzoic acid (PABA)
What do sulfa drugs do?
Binds to and inhibit the enzyme that
converts PABA to folic acid
True or False: Humans do not synthesize folic acid; therefore, sulfa drugs only affect bacteria.
True
True or False: Bacteria do not transport folic acid
True
Who screened 10,000 strains of soil bacteria and fungi for their ability to inhibit growth or kill bacteria and discovered streptomycin?
Selman Waksman
True or False: Streptomycin is produced by Streptomyces
griseus, a soil bacterium
True
Successful antimicrobial compounds exhibit _______________.
Selective toxicity
True or False: Many compounds have side effects at high concentration.
True
True or False: Some drugs cause allergic responses.
True
________________ are effective against many species.
Broad spectrum
______________ kills Gram-positive and Gram-negative bacteria.
Ampicillin
True or False: Penicillin is only effective against gram positive bacteria.
True
_______________ is clinically useful only against Mycobacterium tuberculosis
Isoniazid
__________ are antibiotics that kill target organisms
Bactericidal
____________ are antibiotics that prevent the growth of organisms and let the body’s immune system dispatch the intruding microbe.
Bacteriostatic
What factors need to be considered when administering antibiotics?
- The relative effectiveness of different antibiotics on the
organism causing the infection. - The average attainable tissue levels of each drug.
- The route of administration – oral/intravenous
_______________ can be taken orally and will distribute to tissues.
Cefixime
_______________ is effectively distributed to tissues when given
intravenously (IV).
Ceftriaxone
__________________ is the lowest concentration of the drug that prevents growth of an organism.
minimal inhibitory concentration (MIC)
How do we measure MIC?
Tested by serial dilution of antibiotic
What are benefits of the strip test?
- avoids the need for dilutions.
- contain a gradient of antibiotic
- placed on an agar plate freshly
seeded with a dilute lawn of bacteria
_____________ is also the point at which the elliptical zone of inhibition intersects with the strip.
MIC
True or False: Individual MIC determinations are impractical
True
_______________ tests strain sensitivity to multiple antibiotics. It uses a series of round filter paper disks
impregnated with different antibiotics. A dispenser delivers up to 12 disks to the surface of an agar plate covered by a bacterial lawn.
The Kirby-Bauer assay
____________________ reflects relative sensitivity. It is measured around each disk, and the
results are compared with a table
Diameter of zone of inhibition
What aspects are targeted by antibiotics?
*Cell wall synthesis
* Cell membrane integrity
* DNA synthesis
* RNA synthesis
* Protein synthesis
* Metabolism
Poking holes in the ________________ is an effective way to kill bacteria.
cell membrane
_______________ is a cyclic peptide produced by Bacillus brevis that inserts into membranes as a dimer. It also forms a leaky cation channel that disrupts ion concentration gradients
Gramicidin
True or False: Gramicidin is used only topically,
True
____________ is a polypeptide produced by Bacillus polymyxa . It is a positively charged polypeptide ring binds to the outer (lipid A) and inner membranes of bacteria.
Polymyxin
True or False: Polymyxin is also used only topically.
True
____________ is lipopeptide produced by Streptomyces roseosporus that aggregates in the membranes of Gram-positive bacteria. It forms an ion channel that leaks potassium ions
Daptomycin
True or False: Daptomycin is effective against MRSA.
True
______________ is an antibiotic that blocks bacterial topoisomerases such as DNA gyrase and
topoisomerase IV which leads to the disruption of DNA replication.
True
____________ is an example of a prodrug (inactive until metabolically processed in the body) that is metabolized by cofactors ferredoxin and flavodoxin, and is effective against anaerobic bacteria and protozoa.
Metronidazole
_________ are the basis of selective toxicity that do not exist in mammalian cells.
Bacterial cell walls
__________________ are derived from the amino acids, cysteine and valine, which are condensed by
fungal enzymes to form a beta-lactam ring structure.
Beta-lactam Antibiotics
True or False: The beta-lactam ring chemically resembles the D-Ala-D-Ala piece of peptidoglycan which allows penicillin to bind to and inhibit the transpeptidase enzyme that cross-links peptidoglycan chains.
True
What are two ways bacteria can develop a resistance to beta-lactam antibiotics?
a beta-lactamase enzyme that cleaves the critical
beta-lactam ring or an altered transpeptidase that no longer binds beta-
lactam antibiotics
Antibiotics are considered _______________.
secondary metabolites
In what stage are antibiotics produced?
stationary phase
True or False: Genes encoding some of these drug resistance mechanisms have been
transferred to pathogens.
True
What are three basic antibiotic resistance strategies?
- Keep the antibiotic out of the cell.
- Prevent the antibiotic from
binding to its target. - Dislodge bound antibiotic from
its target.
Antibiotic resistance genes can be ______________, or __________________.
plasma borne or part of the chromosome
What are three ways in which bacteria keeps antibiotics out of the cell?
Bacteria can destroy the antibiotic before it enters
the cell or decrease membrane permeability
across the outer membrane. They can also pump antibiotics out of the cell.
True or False: The beta-lactamase enzyme
specifically destroys penicillins.
True
True or False: Gram-negative bacteria can express alternative outer membrane porins
with pores too narrow to allow drug penetration.
True
True or False: Multidrug resistance (MDR) efflux pumps are particularly dangerous because they can pump out many different types of antibiotics.
True
What are two ways in which bacteria prevent the antibiotic from binding to its target?
They can modify the target so that it no longer binds the antibiotic or add modifying groups that inactivate the
antibiotic.
True or False: Enzymes are used to modify and inactivate antibiotics.
True
True or False: Bacteria can dislodge an antibiotic already bound to its target?
True
_____________ organisms can produce proteins that bind to ribosomes and dislodge antibiotics.
Gram positive (+)
