ch 13

Question 1

Cidal vs. static agents

Answer 1

cidal agents: kill microbes
-Bactericidal, algicidal, fungicidal, virucidal, depending on what type of microbe is killed.

static agents: inhibit or control growth
-Bacteriostatic, algistatic, fungistatic, virustatic, depending on what type of microbe is inhibited.

Question 2

Factors influencing the speed of lethal damage

Answer 2

• the initial population size (The larger the population, the longer it takes to decrease it to a specific number.)
• population composition (i.e., are spores involved?)
• agent concentration or dose for radiation
• duration of exposure
• presence of organic material (blood, feces) that can inhibit disinfectant action; organic load

Question 3

Name examples of physical control agents

Answer 3

• temperature extremes
• pressure (usually combined with temperature)
• filtration
• irradiation

Question 4

Factors influencing the efficacy of a chemical agent

Answer 4

• the presence of organic matter. Chemicals will bind to inert organic material, lowering its effectiveness against microbes.
• the kinds of organisms present. Ideally should be effective against a broad range of pathogens.
• Corrosiveness. Should not corrode the surface (nonliving or living).
• stability, odor, and surface tension. Should be stable upon storage, neutral or pleasant odor, low surface tension.

Question 5

What ways are used to determine efficency

Answer 5

h

Question 6

Name examples of chemical control agents

Answer 6

h

Question 7

Define Selective Toxicity

Answer 7

Scientists realized that successful antimicrobials should exhibit selective toxicity (the “magic bullet”) by killing or inhibiting the pathogen but not the host.

Selective toxicity is possible because key aspects of a microbe’s physiology are different from those of eukaryotes (example: bacterial cell wall).

Even with a high degree of selective toxicity, some antibiotics have unintended side effects that harm the patient.

Question 8

Bacteriostatic, Bactericidal and which would you use for a gram(- )infection and why?

Answer 8

-Bactericidal drugs will kill the target microbes, whereas -bacteriostatic drugs merely prevent their growth.

Question 9

How is minimal inhibitory concentration determined and defined?

Answer 9

The in vitro effectiveness of an agent is determined by how little of it is needed to stop growth.

This is measured in terms of the antibiotic’s minimal inhibitory concentration (MIC).

The MIC is defined as the lowest concentration of the drug that will prevent the growth of an organism.

Question 10

Chemotherapeutic index definition and know that the higher the index, the safer the drug.

Answer 10

The therapeutic dose is the minimum dose per kg of body weight that stops pathogen growth.

The toxic dose is the maximum dose tolerated by the patient.

The ratio of the toxic dose to therapeutic dose is called the chemotherapeutic index. The higher the chemotherapeutic index, the safer the drug.

Question 11

Lower index means more toxic levels are needed.

Question 12

Synergism and Antagonism

Answer 12

Synergistic drugs may work poorly when they are given individually but very well when combined (combined effect is greater than additive effect).

The mechanisms of action of antagonistic drugs interfere with each other and diminish their effectiveness.

Question 13

Modes of action for antibiotics

Answer 13

Antibiotics exhibit selective toxicity because they disturb enzymes or structures unique to the target cell.

Mechanisms include:

• cell wall synthesis -cell membrane integrity
• DNA synthesis -RNA synthesis
• protein synthesis metabolism

Question 14

Penicillin is the only antibiotic for which you need to know the mode of action

Question 15

Penicillin inhibits peptidoglycan synthesis and therefore cell wall synthesis, since peptidoglycan is part of the cell wall.

Question 16

Beta-lactam ring of penicillin can be broken by beta-lactamase, an enzyme that some bacteria possess. This inactivates the drug so that it cannot exert its effects on the bacterial infection.

Question 17

Four ways that microbes can become resistant to antibiotics

Answer 17

-Modify the target so that it no longer binds the antibiotic.
incorporated into a plasmid.
-Destroy the antibiotic before it gets into the cell.
ex: the enzyme beta-lactamase (penicillinase)
-Add modifying groups that inactivate the antibiotic.
ex: enzymes that modify and inactivate aminoglycosides
-Pump the antibiotic out of the cell using specific or nonspecific transport proteins.

Question 18

How they obtain resistance and actions that you can take to limit resistance.

Answer 18

Resistance can arise spontaneously through mutation or gene duplication followed by random mutations that “repurpose” the duplicated gene or genes.
MDR efflux pumps evolved from genes encoding other transport mechanisms.

Once a mechanism of resistance is developed, gene transfer mechanisms such as conjugation can move the genes from one organism to another and from one species to another.
Transfer is particularly easy if the gene has been incorporated into a plasmid.