Microbiology Homework Chapter 9A

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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


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