Week 4/5 Microbial Growth and Control

Question 1

How to kill microbes: Chemotherapeutic agents

Answer 1

Chemical agents used to treat a disease, it is antibacterial, antifungal, and antiviral.

Question 2

What is selective toxicity ?

Answer 2

The ability of a drug to only inhibit the pathogen and not damage the host.

Question 3

What is Therapeutic dose ?

Answer 3

The drug level needed to kill the pathogen in a human being.

Question 4

What is toxic dose ?

Answer 4

Too high of a drug level that becomes toxic to humans

Question 5

What is Therapeutic index ?

Answer 5

Ratio of toxic dose to therapeutic dose

Question 6

Chemotherapeutic agents side effects ?

Answer 6

the undesirable effects of the drug on the host cell.

Question 7

What is a narrow spectrum drug ?

Answer 7

A drug that attacks only a few pathogens/ specific organisms

Question 8

What is a broad spectrum drug ?

Answer 8

A drug that attacks a wide range of pathogens/ specific organisms

Question 9

What is the minimal inhibitory concentration (MIC)

Answer 9

The lowest concentration of the drug needed to kill the pathogen. Used in blood diseases so the cells don’t get lysed and create blood toxins.

Question 10

What is the minimal lethal concentration ? (MLC)

Answer 10

The lowest concentration of the drug that kills the pathogen. Used in skin bacterial infections to fully lyse the bacteria.

Question 11

How do you determine the effectiveness of antimicrobials using the dilution susceptibility test ?

Answer 11

Used to determine the minimal concentration of the antibiotic needed to kill the pathogen. (MIC)

Bacteria are inoculated into different concentrations of the antibiotic. The first tube that has the lowest of antibiotic showing no growth is the MIC.

Question 12

How do you determine the effectiveness of antimicrobials using the disk diffusion test ?

Answer 12

Have a plate with bacteria growing, and disks with antibiotics are added to inhibit growth. The disks will have a halo of clear agar indicating no bacterial growth and that the antibiotic worked.

Question 13

What do antibiotics target ?

Answer 13

• Inhibit cell wall synthesis
• inhibit protein synthesis
• stop metabolism
• inhibit the synthesis of nucleic acids

Question 14

Describe Penicillin (B-lactam)

Answer 14

Effective against gram +ve bacteria
acts on growing bacteria

It blocks the enzyme that catalyzes transpeptidation ( cross-links of NAM and NAG) and prevents the synthesis of the cell wall so the cells lyse.

Question 15

Why is there a range of B-lactam antibiotics ?

Answer 15

Antibiotics like penicillin have been modified so that they can work along with bacteria that mutate and become resistant to certain antibiotics.

Question 16

Cephalosporins - chemotherapeutic agent

Answer 16

Work similar to penicillin, this is a broad spectrum antibiotic so it works on a lot of bacteria/pathogens. Works on G+ve and G-ve bacteria.

Question 17

Vancomycin/Teicoplanin

Answer 17

Works on gram +ve bacteria. It stops cell wall synthesis it binds tightly to the peptide chain in peptidoglycan.

Used to treat antibiotic resistant bacteria, as it doesn’t bind to proteins so mutating the protein structure doesn’t affect it.

Question 18

Aminoglycosides

Answer 18

Have a cyclohexane ring and amino sugars. They bind to the 30s ribosomal subunit and interfere with protein synthesis, by causing misreading of the mRNA.

Works against Gram-ve aerobic bacteria and facultative anaerobic bacteria

Question 19

Tetracyclines

Answer 19

A 4 ring structure, with a variety of side chains that are able to bind. Wide spectrum antibiotic.

Binds to the 30s ribosomal subunit, and stops the aminoacyl tRNA from binding to the A site in the ribosome.

Bacteriostatic

Question 20

Macrolides

Answer 20

Bacteriostatic

Contain 12-22 carbon lactone rings that are linked to one or more sugars.

Bind to 23s rRNA of the 50s ribosomal subunit. and inhibits peptide chain elongation.

Question 21

Sulfa Drugs

Answer 21

Metabolic drugs

Many pathogens make folic acid and this drug mimics a component of folic acid called P-aminobenzoic acid (PABA). They inhibit enzymes that make folic acid.

Bacteriostatic

Question 22

Trimethoprim

Answer 22

Synthetic antibiotic that interferes with folic acid production. They can be combined with sulfa drugs to be more effective

Question 23

Quinolones

Answer 23

Broad spectrum

A synthetic drug containing 4 quinolone ring

It inhibits bacterial DNA gyrase and topoisomerase 2.

Bactericidal

Question 24

Lipopeptides

Answer 24

Only effective against gram +ve organisms

it enters the membrane and aggregates near phosphatidyglycerol, forms holes in the membrane of bacteria.

Question 25

Antifungal drugs

Answer 25

Disrupt membrane permeability
inhibit sterol synthesis
disrupt spindle formation
inhibit nucleic acid and protein synthesis

Question 26

Antifungal - Amphotericin B & Clotrimazole

Answer 26

Bind to the fungal steroid ergosterol and cause the membrane to leak.

Question 27

Antiparasitic drugs

Answer 27

Used to treat malaria and helminths
contain peroxide
can cause antibiotic resistance

Question 28

Antimicrobial resistance

Answer 28

When you get a bacterial infection, as the bacteria grow they mutate and some are more naturally resistant to antibiotics than others. After selection/ taking antibiotics you are left with a few resistant bacteria that can re-populate. The immune system can take care of the last few bacteria.

If you stop taking your antibiotics before the infection clears and you have Ab resistant bacteria the immune system cant kill them and they will populate. They can transfer their Ab resistance to other bacteria.