Microbiology Homework Chapter 9A
Place the steps of the Etest in the correct order.
1. Innoculate surface of agar plate with bacteria 2. Place Etest strips on surface of agar plate 3. Incubate plates 24-48 hours 4.Determine MIC
In the disk diffusion test, zone-width is influenced by
-Diffusion rate of antibiotic -initial concentration of antibiotic -Solubility of antibiotic
Which two of the following statements about the dilution susceptibility test are true?
-MIC is determined by lack of growth in a tube with minimum amount of antibiotic -MLC determined by lack of growth in antibiotic free broth that was inoculated from previous non-growth tube with lowest concentration of antibiotic
Place the steps of the broth dilution test to determine the MLC in the correct order.
1. Inoculate Broth tubes containing serially diluted antibiotic 2. Incubate cultures in antibiotic tubes for 16 to 20 hours 3. Observe tubes to with the lowest concentration in which there was no growth represents MIC 4. Inoculate broth tubes (no antibiotic) with samples that did not grow in tubes with anitbiotics 5.Incubate culutres in broth without antibiotics 6. Obserce tubes: tube with the lowest antibiotic concentration in which there was no growth represent MLCTrue or false: In the disk diffusion test, zone width is a measure of bacterial susceptibility.
Place the steps of the disk diffusion test in the correct order.
1. Inoculate surface of Mueller-Hinton agar plate with bacteria 2. Place antibiotic infused test disk onto agar surface 3. Incubate plates 16-18 hours at 35C 4. Measure zone 5. Determine MLC
Place the following antimicrobial agents in the correct order of their development as pharmaceuticals (from earliest to latest).
1. Salvarson 2. Sulfonamides 3. Penicillin 4. Streptomycin 5. Tetracycline
What is the approximate concentration of antibiotic when the inhibitory zone diameter is 14 mm?
16
Which of the following are broad spectrum antibiotics?
Amoxicillin Ampicillin
In this molecule, a cephalosporin, which component is the β-lactam ring?
B
Which two of the following characteristics apply to aminoglycosides?
Bind to 30S ribosomal subunit Synthesis of abnormal proteins
The aminoglycoside antibiotics are characterized by the presence of amino sugars and a _____.
Cyclohexane ring
Which two of the following statements are correct?
Different organisms may have differing susceptibilities to a particular drug. Streptomycin would be a good choice for chemotherapy against an organism that produces a 20 mm zone of inhibition.
If you were suffering a bacterial infection, which of the five antibiotics tested here would you *not* want to clear the infection?
E
An antibiotic susceptibility test that uses small pieces of plastic that contain an antibiotic gradient to determine the MIC is called the
Etest
This image illustrates the _____ to determine antibiotic susceptibility and MIC.
Etest
True or false: The lower the therapeutic index, the better the chemotherapeutic agent is.
False
Which three of the following scientists were awarded the Nobel prize for the discovery and production of penicillin?
Fleming Florey Chain
Many new antimicrobial agents have been discovered in which two soil inhabitants?
Fungia Bacteria
Which host system eliminates pathogens targeted by static antimicrobial agents?
Immune
The term bactericidal means that the antimicrobial agent bacteria, and bacteriostatic means that it reversibly the growth of the bacteria.
Kills Inhibits
William and A. W. developed a disk diffusion test that bears their names and is still in widespread use today.
Kirby Bauer
Which of the following is NOT a side effect of aminoglycoside antibiotic use?
Liver damage
Which of the following are possible side effects of aminoglycoside antibiotic use?
Loss of balance Allergic reaction
In the dilution susceptibility test, the lowest concentration of antibiotic that results in no growth of the test bacterium is the _____.
MIC
For consistency, the medium used for disk diffusion tests is _____ agar.
Mueller-Hinton
The era of modern antimicrobial chemotherapy began with the work of _______, who put forth the concept of a "magic bullet," a chemical that would selectively destroy pathogens without harming human cells.
Paul Ehrlich
Match each antimicrobial agent with the person or persons who discovered it.
Penicillin-Duchesne and Flemming Sulfonamide-Domagk Streptomycin-Waksman Salvarsan-Ehrlich and Hata
Which of the following is NOT a likely source antimicrobial agents?
Plant natural products
Which of the following statements is correct?
Pseudomonas is less susceptible to carbenicillin than E. coli.
Naturally occurring antibiotics that have been chemically modified by the addition of chemical groups are called antibiotics.
Semi-synthetic
Which of the following are typical sources of antimicrobial agents?
Semisynthetic agents - chemically modified naturally occurring antibiotics Natural products of soil bacteria and fungus Synthetic agents - products of chemical reactions
Cidal-Kills the target
Static-Reversibly inhibits the growth of the target
Selective toxicity Death or inhibition of pathogen with minimal damage to host
Therapeutic dose Drug level required for treatment of an infection
The degree of selective toxicity can be expressed in terms of
Therapeutic dose Toxic dose
Which of the following statements about carbapenems and monobactams is false?
These drugs are heavily used clinically.
True or false: In the disk diffusion test, zone width is a measure of bacterial susceptibility.
True
The drug of last resort for the treatment of antibiotic resistant Staphylococcus aureus is
Vancomycin
Which of the following is a narrow spectrum antibiotic?
Vancomycin
Which of the following is considered a "drug of last resort" when treating antibiotic resistant Staphylococcus aureus?
Vancomycin
A zone of inhibition is _____.
a clear ring around an antibiotic disk in the Kirby-Bauer assay
Which three of the following are believed to be mechanisms of action of penicillin?
activate bacterial autolytic enzymes inhibit the transpeptidation reaction in peptidoglycan synthesis stimulate holins to form holes in the plasma membrane
Based on its chemical structure, the antibiotic shown here belongs to the class of drugs termed ____
aminoglycosides
Match each antibiotic with its mechanism of action.
aminoglycosides-bind to the 30s RIBSOMAL SUBUNIT Macrolides-bind to the 50s RIBSUNIT oXAZ-REVE
Which of the following is NOT a likely source antimicrobial agents? Chemical modification of antibiotics
ant natural products
The therapeutic index of a protein synthesis inhibitor is less than the therapeutic index of a cell wall inhibitor because _____.
bacterial cells and host cells both use ribosomes for protein synthesis
Vancomycin has the same target as β-lactam antibiotics, the transpeptidation reaction in peptidoglycan synthesis, but it differs in that it _____.
binds to the enzyme's substrate
Penicillin disrupts cell wall formation by _____.
blocking the formation of peptidoglycan cross links
The sulfonamides inhibit the growth of a wide variety of bacteria and are classified as -spectrum drugs.
broad
Drugs that are effective against a wide variety of pathogens are called _____ drugs.
broad-spectrum
The two newest classes of β-lactam drugs are
carbapenems monobactams
The most selective antibiotics in use target the bacterial .
cell wall
The most selective antibiotics target _____.
cell wall synthesis
All aminoglycoside antibiotics contain a(n) ring and amino sugars.
cyclohexene
The Kirby-Bauer test is the most commonly used type of _______.
disk diffusion test
The drugs that target the cell wall have a high therapeutic index because human cells _____.
do not have cell walls
The concept of a "magic bullet," a chemical that would selectively destroy pathogens without harming human cells, was put forth by Paul Blank 1Blank 1, Correct Unavailable, whose research sparked the era of modern antimicrobial chemotherapy.
ehrlich
True or false: Both penicillins and semisynthetic penicillins are substrates for beta-lactamases.
false
The tetracycline antibiotics are characterized by a _____.
four ring structure with various side chains attached
As a general rule, the (greater/smaller) therapeutic index, then the better the antimicrobial agent.
greater
As a general rule, the therapeutic index, then the better the antimicrobial agent.
greater
In the Kirby-Bauer assay pictured here, the bacterial strain is _____.
growing all over the surface of the plate
A drug that disrupts a microbial structure or function not found in host cells has a _____ therapeutic index.
higher
Static antimicrobial agents require the activities of the host response to destroy the targeted pathogen.
immune
In the dilution susceptibility test, the minimum concentration is the lowest concentration of antibiotic that results in no growth after incubation.
inhibitory
The minimal concentration is the level of an antimicrobial agent required to stop the growth of a targeted pathogen.
inhibitory
Both minimum concentration and minimum concentration can be determined using the dilution susceptibility test.
inhibitory letha;
Penicillin is considered to be the first true antibiotic, meaning that it _____.
is a natural microbial product
Penicillin has a high therapeutic index because _____.
its cellular target, peptidoglycan, is absent from host cells
Most penicillin resistant bacteria produce enzymes called penicillinases that hydrolyze the β-
lactam
The most critical portion of the cephalosporin molecule is the β- , which is essential for the antimicrobial activity of the drug.
lactam ring
The therapeutic index of a protein synthesis inhibitor is _____ the therapeutic index of a cell wall inhibitor.
less than
The minimal concentration is the level of an antimicrobial agent required to kill a targeted pathogen.
lethal
Bacteria sensitive to penicillin are killed as a result of osmotic
lysis
Which two of the following antibiotics inhibit protein synthesis by binding to the 50S ribosomal subunit?
macrolides chloramphenicol
The concentration of drug necessary to prevent the growth of a pathogen is called the _____.
minimal inhibitory concentration
The concentration of drug necessary to kill a pathogen is called the _____.
minimal lethal concentration
What information do you get from the Etest that you do not get from the Kirby-Bauer test?
minimum inhibitory concentration
The dilution susceptibility test can be used to determine
minimum inhibitory concentration minimum lethal concentration
Penicillin G, penicillin V, and methicillin are spectrum antibiotics.
narrow
Vancomycin is a spectrum antibiotic.
narrow
Vancomycin is classified as a spectrum drug because it is only effective against Gram positive bacteria.
narrow
Drugs that are only effective against a limited variety of pathogens are called _____ drugs.
narrow-spectrum
The ultimate result of penicillin treatment of sensitive bacteria is cell-death resulting from ______.
osmotic lysis
Fleming, Florey, and Chain were awarded the Nobel prize in 1945 for the discovery and production of
penecillin
The mechanism of action of is three-fold: It inhibits the transpeptidase reaction in peptidoglycan biosynthesis, activates bacterial autolytic enzymes, and stimulates holins to form holes in the plasma membrane.
penecillin
The first true antibiotic (a natural microbial product) to be used was
penicillin
The most critical component of the vancomycin molecule is the ________ portion of the glycoprotein, which is essential for the antimicrobial activity of the drug.
peptide
The most critical component of the vancomycin molecule is the ________ portion of the glycoprotein, which is essential for the antimicrobial activity of the drug. sugar
peptide
The structural component of the vancomycin molecule that is critical for antimicrobial activity is the ________.
peptide portion
It is thought that penicillin blocks the bacterial enzymes that create crosslinks between polymers (strands) in the cell wall.
peptidoglycan
The mechanism of action of this antibiotic on bacterial cells is to inhibit _____.
peptidoglycan synthesis
On this Petri dish showing the interaction of two microorganisms, the organism indicated by the letter B is _____. producing c
poducing compounds active against organism A
n the Kirby-Bauer assay pictured here, the antibiotic is _____.
present in the white disks Reason: The white disks were used to apply antibiotic to the plate, and while some has diffused into the surrounding zones, there will still be significant amounts in the disks.
On this Petri dish showing the interaction of two microorganisms, the organism indicated by the letter B is _____.
producing compounds active against organism A
Aminoglycosides interfere with _____.
protein synthesis
The antibiotic shown here inhibits bacterial growth by disrupting _____.
protein synthesis
In the assay shown here, the MIC is determined by _____
reading where the zone of inhibition intersects the Etest strip
A successful antimicrobial agent has , the ability to kill or inhibit microbial pathogens with little or no damage to the host.
selective toxicity
The ability to kill or inhibit microbial pathogens while causing minimal damage to the host is called _____.
selective toxicity
Naturally occurring antibiotics that have been chemically modified are called ______.
semi-synthetic
The first drug to successfully treat tuberculosis was _____.
streptomycin
An inhibitory zone diameter of 22 mm would indicate that this organism is _____ to this hypothetical drug.
susceptible
On this Petri dish showing the interaction of two microorganisms, the organism indicated by the letter A is _____.
susceptible to compounds produced by organism B
The are a family of antibiotics that are characterized by a four ring structure to which a variety of side chains are attached.
tetracyclines
The semisynthetic penicillins nafcillin, oxacillin, and methicillin are more difficult for β-lactamase enzymes to degrade because _____.
they have bulkier side chains than natural penicillin
The therapeutic index is the ratio of the _____.
toxic dose to therapeutic dose
The therapeutic index is the ratio of the
toxic, therapeutic
True or false: The tetracyclines are bacteriostatic.
true
Streptomycin is important historically because it was the first drug to successfully treat _____.
tuberculosis
Which of the following antibiotics inhibits the transpeptidation reaction of peptidoglycan synthesis, but lacks a β-lactam ring in its structure?
vancomycin
A clear area that forms around an antibiotic disk after incubation with a bacterial strain is called a of inhibition.
zone
The structural component of the cephalosporin molecule that is critical for antimicrobial activity is the _________.
β-lactam ring
The basis of penicillin resistance in bacteria is the ability to produce enzymes called penicillinases or _______.
β-lactamases
