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Chapter 10 – Controlling Microbial Growth in the Body: Antimicrobial Drugs
1
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 Applying an antimicrobial agent that is more toxic to a pathogen than to the pathogen’s
host
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List six mechanisms by which antimicrobial drugs affect pathogens
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3
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 Penicillin and cephalosporin, irreversibly bind to enzymes responsible for the NAM peptide
bonding
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 Bacitracin blocks the transport of NAG and NAM from cytoplasm to the cell wall
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Describe the six different mechanisms by which protein synthesis is inhibited by antimicrobial drugs
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 Tetracycline blocks the tRNA docking site (A site), which prevents the addition of amino
acids
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 Lincosamides bind to a different place, preventing the ribosome to move the string of
mRNA codons along
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 Oxazolidinone block the start of translation by preventing the large subunit to form the
initiation complex
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Describe how nystatin and amphotericin B interfere with cytoplasmic membranes
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6
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

Sulfonamides are structural analogs to PABA, so it competes for the active site on the
enzyme for production of dihydrofolic acid
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7
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

Analogs have structural similarities in shape and size of each other, so they fit in the same
active site
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Describe how amantadine inhibits viral infection
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 Amantadine is an antiviral drug that functions as a weak organic base, neutralizing the
acidic conditions
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How do nucleoside (and nucleotide) analogs inhibit nucleic acid function? Example: AZT
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 Changing the shape prevents further replication, transcription, or translation of viral or
cancer DNA or RNA
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Describe the action of antimicrobial attachment antagonists
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11
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 They inhibit DNA gyrase, an enzyme needed for correct coiling and uncoiling of replicating
DNA of bacteria
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Distinguish narrow-spectrum drugs from broad-spectrum drugs in their targets and side effects
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(ex: penicillin)
 Drugs with a high variety of targets are considered broad-spectrum drugs
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13
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k
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Kirby-Bauer test), Etest, MIC, and MBC tests
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o After incubation, the effective drugs inhibit the growth of bacteria as seen in figure
to left
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 Minimum Inhibitory Concentration (MIC) Test
o This test suggests the smallest amount of drug that inhibits growth and
reproduction of a pathogen
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o After inoculation, cloudiness indicates growth, clear tubes indicate lack of growth or
death
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Minimum Bactericidal Concentration (MBC) Tests
o A MBC test determines the amount of drug required to kill the microbe
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o The lowest concentration with no bacterial growth is the MBC
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Discuss the advantages and disadvantages of the different routes of administration of antimicrobial
drugs
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 Oral administration - Pros: no needles required
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 Intramuscularly (IM) - Pros: allows drug to slowly diffuse into many blood vessels within
muscle
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 Intravenously (IV) - Pros: delivers drug directly into bloodstream via a needle or catheter
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15
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 Toxicity: Some drugs, like Polymyxin and aminoglycosides, can be toxic to the kidneys, liver,
or nerves
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 Allergies: Penicillin can have an allergic reaction called anaphylactic shock
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o Long term use of broad-spectrum drugs can cause growth of Candid albicans in
vagina or mouth or growth of Clostridium difficile in the colon
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Describe how populations of resistant microbes can arise
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17
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 Resistant cells simply possess R plasmids that produce necessary proteins needed for
resistance
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List seven ways by which microorganisms can be resistant to antimicrobial drugs
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o …may alter itself so that antimetabolites either cannot attach or at least less
effectively
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o
o
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…may pump the antimicrobial out of the cell before the drug can act
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Mycobacterium tuberculosis synthesize MfpA protein that protects its DNA
molecule
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List two ways that genes for drug resistance are spread between bacteria
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