Free «Antibiotic Sensitivity» Essay Sample

A. Define the term "selectively toxic." Why is it an important feature of antimicrobial agents? 

A substance or drug is said to be selectively toxic if the agent used in it is able to inhibit or kill the microorganism that is meant to without causing any other harm to the host that has taken the drug or substance. This is very important to microbial agents in that it enables these agents to inhibit or kill a microorganism by interacting with microbial functions or structures different from those of the host thereby showing little or no effect to the host.

B. What are broad and narrow spectrum antimicrobials? What are the pros and cons of each?

Broad spectrum antimicrobials are drugs that are effective against a wide variety of both gram positive and gram negative bacteria. A good example of such includes tetracycline, streptomycin, ampicilin and sulfonamides. On the other hand narrow spectrum antimicrobials are only effective against specific bacteria it may be just gram positive bacteria, just gram negative bacteria or only a few species. An example of such includes penicillin G, clindamycin and gentamicin.

Narrow spectrum microbials are normally better to use because they cause less damage to the body's normal flora. They are less likely to cause drugs resistant stains of microorganisms because they are specific in nature and are less likely to cause superinfection by opportunistic microorganisms like yeast infections. The main disadvantages are that Narrow spectrum microbials sometimes are more prone to allergic reaction to the host.

Broad spectrum antimicrobials on the other hand also have there own advantages in that they are able to deal with more than one kind of bacteria and as such one does not have to use drugs indiscriminately reducing chances of allergic recations and drug toxicity. The main disadvantage is that they cause more harm to the body's normal flora.

C. What is direct selection?

Direct selection is the selection of antibiotic-resistant normal floras in an individual whenever this individual is given an antibiotic. This process is normally accelerated significantly by either improper use or the overuse of antibiotics.

D. What is the difference between an antibiotic and an antimicrobial chemical?

Antibiotics are substances that are produced as metabolic products of one Microorganism which are able to inhibit or kill other microorganisms. On the other hand Antimicrobial chemicals are chemicals that are synthesized in a laboratory and can be used therapeutically on microorganisms.

E. What is the mode of action for each of the following:

(a). Bacitracin: works by inhibiting   peptidoglycan synthesis in actively-dividing bacteria which normally results in osmotic lysis.

(b). Nystatin: this by altering the cytoplasmic membrane of microorganisms which would result in leakage of cellular materials

(c). Tetracycline: contains agents that prevent bacteria from synthesizing structural proteins and enzymes

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(d). Ciprofloxin: contains agents that  inhibit one or more enzymes in the DNA synthesis pathway

F. Describe three mechanisms by microbes might become resistant to the action of an antimicrobial drug?

Microbes may become resistant by producing enzymes that will detoxify or inactivate the antibiotic such as penicillinase and other beta-lactamases.

Microbes may also alter the target site in the bacterium to reduce or block binding of the antibiotic in the process producing a slightly altered ribosomal subunit that still functions but to which the drug can't bind.

Microbes may also Prevent the transport of the antimicrobial agent into the bacterium thereby producing an altered cytoplasmic membrane or outer membrane.

G. Why do you think that neglecting to finish a prescribed course of antibiotics might contribute to the rise of antibiotic resistance?

Neglecting to finish a prescribed course of antibiotics enables  the selection of antibiotic-resistant normal floras within an individual then  later on, these resistant normal floras  transfer resistance genes to the pathogens that enter the body enabling them to resist this antibiotics.

H. What is a tube dilution test, how is it used to determine susceptibility?

Tube dilution test is one of the tests that can  be used to tell which antimicrobial agent is most likely to combat a specific pathogen .this test is conducted by preparing  a series of culture tubes  where each contains a liquid medium and a different concentration of an antimicrobial agent. These tubes are then inoculated with the test organism then they are incubated. After the incubation they are examined for growth. The minimum inhibitory concentration is determined from this. Also by sub culturing the tubes showing no growth into tubes that have medium and no antimicrobial agent helps determine the minimum bactericidal concentration.

I. Define the following:

(a). Minimum Inhibitory Concentration (MIC) this is the lowest concentration of antimicrobial agent that is capable of preventing growth of the organism undergoing the tube dilution test

(b). Zone of Inhibition. This is the area surrounding the high potency disk of a chemotherapeutic agent where growth is inhibited in an agar diffusion test.

J. What were the results of your Kirby-Bauer test for S. epidermidis?

S. epidermidis was sensitive to Novobiacin

s.epidermidis was resistant to penicillin

s. epidermidis  was intermediate in the case of Gentamicin

K. use colored pencils to sketch what YOU see under the microscope

L. Purpose: This experiment is designed to determine the antimicrobial susceptibility in order to determine which antimicrobial agent may be used against a specific strain of bacterium.

M. Procedure: 

1.Disinfect work area

2.Using the nutrient agar plate made previously, and a sterile swab, coat the

surface of the agar thoroughly with liquid S. epidermidis leaving no unswabbed areas

3. Turn the  agar plate 90 degrees then  repeat the swabbing process.

4. Let  the plate  dry in an upright posture  for 5 minutes to allow the S. epidermidis culture to

absorb completely.

5. Using a marker on the outside bottom surface divide the dish into three sections triangular segments.

6. Label the  sections as 1. novobiacin, 2.penicillin, and 3. gentamicin respectively

7. using tweezers transfer the antibiotic disks to the surface of the agar plate. Placing each disk into the center of the corresponding section of the agar plate.

8. Incubate the agar dishes upside down at 35o C - 37o C for 24 to 48 hours

9.make the appropriate Interpretations of the results

N. Observations:

Antibial agent

zone diameter in millimeters

S. epidermidis sensitivity.










O. Conclusions:

S. epidermidis was sensitive to Novobiacin

s.epidermidis was resistant to penicillin

s. epidermidis  was intermediate in the case of Gentamicin


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