Antibiotic Sensitivity lab A. Define the term selectively toxic. Why is it an important feature of antimicrobial agents? Selective toxicity is the ability of a chemical or drug to kill a microorganism without harming its host. Selective toxicity is important to microbial agents because 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. Narrow spectrum antimicrobials are effective only against gram negative bacteria. Pros and cons of each: Narrow spectrum microbial is normally better to use because they cause less damage to the body’s normal flora. They are less likely to cause drugs resistant strains of microorganisms because they are specific in nature and are less likely to cause super infection by opportunistic microorganisms like yeast infections.
The main disadvantages are that Narrow spectrum microbial sometimes is more prone to allergic reaction to the host. Broad spectrum antimicrobials on the other hand also have their 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 reactions 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. 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. acitracin: works by inhibiting peptidoglycan synthesis in actively dividing bacteria which normally results in osmotic lysis. b. nystatin: exerts its antifungal activity by binding to ergosterol found in fungal cell membranes. Binding to ergosterol causes the formation of pores in the membrane. Potassium and other cellular constituents leak from the pores causing cell death. c. tetracycline: exert their bacteriostatic effect by inhibiting protein synthesis in bacteria. This antibiotic prevents transfer-RNA (tRNA) molecules from binding to the 30S subunit of bacterial ribosomes. . ciprofloxin: Contains agents that inhibit one or more enzymes in the DNA synthesis pathway F. Describe three mechanisms by which 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 neglecting to finish a prescribed course of antibiotics might contribute to the rise of antibiotic resistance? If you don’t finish the medication, all the bacteria causing the infection may not be killed. Then, the infection could come back in that same place or even show up somewhere else. When the bacteria are undertreated, some of them may have enough time to have these mistakes occur in their DNA.
Then, when they multiply, you get a bunch of bacteria that no longer respond to the 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 tube contains a liquid medium and a different concentration of an antimicrobial agent. These tubes are then inoculated with the test organism and then incubated. After the incubation they are examined for growth.
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 the 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