Chapter 10 Controlling microbial growth in the body

Question 1

Chemicals that affect physiology in any manner is called drugs, give some examples

Answer 1

Caffeine, alcohol, and tobacco

Question 2

Drugs that act against diseases are called? (Any chemical to treat or apply to any treatment to treat any human condition)

Answer 2

Chemotherapeutic agents, examples are insulin, anticancer drugs, and drugs for treating infections called antimicrobial agents (antimicrobials)

Question 3

What did Paul Ehrlich (1854-1915) do?

Answer 3

• A visionary germen scientist
• Proposed chemotherapy to describe use of chemicals that selectively kill pathogens while having little or no effect on patient
• He wrote of “magic bullets” that would bind to receptors on germs to bring about their death while ignoring host cells, which lacked the receptor moleucles
• His search resulted in the discovery of one arsenic compound that killed trypanosome parasites & another that worked against the bacterial agent of syphilis.

Question 4

What did Alexander Fleming do?

Answer 4

• British bacteriologist, he reported that antibacterial action of penicillin released from Penicillium mold, which creates a zone where bacteria can’t grow

Question 5

Back in the day Ehrlich’s arsenic compounds were toxic to humans, and penicillin was not available in large quantities to be useful until the late 1940s so what was used instead?

Answer 5

Sulfanilamide, discovered in 1932 by the German chemist Gerhard Domagk was the first practical antimicrobial agent efficacious in treating a wide array of bacterial infections

Question 6

What did Selman Waksman discover?

Answer 6

Other microorganisms that are sources of useful antimicrobials, most notably species of soil-dwelling bacteria in the genus Streptomyces. Waksman coined to term antibiotics to describe antimicrobial agents that are produced naturally by an organism

Question 7

Drugs that are effective against antiviral agents are likely?

Answer 7

Toxic to the host as well because viruses utilize their host cell’s enzymes & ribosomes to metabolize & replicate

Question 8

Because there are many differences between the structure & metabolism of pathogenic bacteria & their eukaryotic hosts, antibacterial drugs make greatest number & diversity of antimicrobial agents. Why are there few anti fungal?

Answer 8

Fewer anti fungal & antiprotozoan drugs are available, why is this? Because fungi, protozoa, & helminths-like their animal & human hosts- are eukaryotic & thus share common features.

Question 9

Antimicrobial drugs can be categorized into several general groups according to their mechanism of action

Answer 9

1) Drugs that inhibit cell wall synthesis
2) Drugs that inhibit protein synthesis (translation)
3) Drugs that disrupt unique components of cytoplasmic membrane
4) Drugs that inhibit general metabolic pathways not used by humans
5) Drugs that inhibit nucleic acid synthesis
6) Drugs that block a pathogens recognition of or attachment to its host

Question 10

Drugs that inhibit cell wall synthesis. These drugs are?

Answer 10

Selectively toxic to certain fungal or bacterial cells, which have cell walls, but not to animals, which lack cell walls

Question 11

Drugs that inhibit protein synthesis (translation) by?

Answer 11

Targeting the differences between prokaryotic & eukaryotic ribosomes

Question 12

Describe how drugs can inhibit the synthesis of bacterial walls

Answer 12

• They prevent cross linkage of NAM subunits which connects to the nag subunits which form the peptidoglycan.
• Beta-lactams- most prominent drug, several types, penicillins & cephalosporins

Question 13

What does the Beta-lactam drug do?

Answer 13

Inhibits synthesis of peptidoglycan bacterial walls by irreversibly binding to the enzymes that cross-link NAM subunits.
* Their functional portions are the beta-lactam rings

Question 14

What are the semisynthetic derivatives of beta-lactams?

Answer 14

It is where chemists have made alterations to natural beta-lactams, such as penicillin G, to create semisynthetic derivatives. In turn they are:

1) More stable in the acidic environment of the stomach
2) More readily absorbed in the intestinal tract
3) Less susceptible to deactivation by bacterial enzymes
4) More active against more types of bacteria

Question 15

The simplest beta-lactams are?

Answer 15

Monobactams, which are seldom used because they are effective only against aerobic Gram-negative bacteria

Question 16

What do the antimicrobials vancomycin and cycloserine do?

Answer 16

They disrupt cell wall formation by directly interfering with particular alanine-alanine bridges that link the NAM subunits in many Gram-positive bacteria. The bacteria that lack these bridges are resistant.

Question 17

What does bacitracin do?

Answer 17

It blocks the transport of NAG and NAM from the cytoplasm out to the wall. Like beta-lactams, vancomycin, cycloserine, and bacitracin result in cell lysis due to the effects of osmotic pressure

Question 18

Why are dormant cells unaffected with drugs that inhibit synthesis of bacterial walls?

Answer 18

Because those drugs prevent bacteria from increasing the amount of cell wall material but have no effect on existing peptidoglycan, they are effective only on bacterial cells that are growing or reproducing

Question 19

What does isoniazid (IHN) and ethambutol do?

Answer 19

They disrupt the formation of my colic acid in Mycobacterium species. These drugs must be administered for months or years to be effective because Mycobacteria typically reproduce only every 12-24 hours

Question 20

Why is the inhibition of protein synthesis significant?

Answer 20

Because cells use proteins for structure & regulation, as enzymes in metabolism, & as channels & pumps to move materials across cell membranes. Thus a consistent supply of proteins is vital for the active life of a cell. All cells use ribosomes to translate proteins using info from mRNA templates

Question 21

Prokaryotic ribosomes differ from eukaryotic ribosomes in structure & size and many antimicrobial agents take advantage of the differences between the ribosomes to?

Answer 21

Selectively target bacterial protein translation without affecting eukaryotes.
However, because some of the drugs affect eukaryotic mitochondria which contain 70s ribosomes like prokaryotes, these drugs can be harmful to animals & humans, especially the active cells of the liver & bone marrow.

Question 22

Both the 30s and 50s subunits of prokaryotic ribosomes play a role in?
Why is this important?

Answer 22

The initiation of protein synthesis, in codon recognition, & in the docking of tRNA-amino acid complexes, & that the 50s subunit contains enzymatic portion that forms peptide bonds.
This is important because in order the understand the actions of antimicrobials that inhibit protein synthesis we need an understanding of the process of translation, because various parts of ribosomes are targets of drugs

Question 23

The antimicrobials that target the 30s ribosomal subunits are?

Answer 23

Aminoglycosides and tetracyclines

Question 24

Aminoglycosides such as streptomycin and gentamicin do what?

Answer 24

Change the shape of the 30s subunit making it impossible for the ribosome to read the codons of mRNA correctly

Question 25

Some amino glycosides and tetracyclines block what?

Answer 25

The tRNA docking site (A site), which then prevents the incorporation of additional amino acids into a growing polypeptide

Question 26

Some antibacterial drugs, such as the short polypeptide gramicidin, disrupt the cytoplasmic membrane of a targeted cell often by?

Answer 26

Forming a channel through the membrane, damaging its integrity. This is also the mechanism of action of a group of anti fungal drugs called polyenes

Question 27

What do the polygenes nystatin and amphotericin B (major drug) do?

Answer 27

They are fungicidal because they attach to ergosterol, a lipid constituent of fungal membranes, in this process disrupting the membrane & causing lysis of the cell. The membranes of humans are somewhat susceptible to amphotericin B because they contain cholesterol, which is similar to ergosterol, though cholesterol does not bind amphotericin B as well as ergosterol

Question 28

Causes change in 30s ribosome shape, so mRNA is misread

Answer 28

Some aminoglycosides, for example streptomycin

Question 29

Block docking site of tRNA

Answer 29

Tetracycline and some aminoglycosides

Question 30

Blocks peptide bond formation

Answer 30

Chloramphenicol

Question 31

Bind to 50s subunit, blocking proper mRNA movement through ribosome, & synthesis stops

Answer 31

Lincosamides or macrolides

Question 32

Azoles, such as fluconazole, and allylamines, such as terbinafine, are two other classes of anti fungal drugs that disrupt cytoplasmic membranes. They act by?

Answer 32

Inhibiting the synthesis of ergosterol, without this the cell’s membrane does not remain intact & the fungal cell dies. These drugs are generally harmless to humans, because human cells don’t have ergosterol