Laboratory Exercise 5: Chemical Antimicrobial Treatments (SS2018) Evaluate the e
ID: 206680 • Letter: L
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Laboratory Exercise 5: Chemical Antimicrobial Treatments (SS2018) Evaluate the effectiveness of common Objectives: After completing this exercise you should be able to ectants/antiseptics household disinf 2. Explain why (and how) phenol coefficients are determined. 3. Do a routine test for checking the effectiveness of antibiotics. Background Control of MOs can be divided into physical and chemical methods (see lecture notes l cells indiscriminate and Lab 9 for a review). Physical means of sterilization usually kill al and cannot be used in many situations. (You would not want to flame or autoclave your hand!) Therefore, a wide variety of chemicals have been developed for controlling bacterial growth where complete sterilization is not feasible. Disinfectants are chemicals used on objects. Antiseptics are chemicals that are used on the skin or wounds to decrease the number of microorganisms. If antimicrobial agents act by actually killing the bacteria, they are called bactericidal agents. If they act by causing temporary inhibition of growth, they a called bacteriostatic agents. The killing effect of any agent is a complex relationship that depends on many variable and this makes it hard to assign a simple number to it. One approach to measuring the effectiveness of a chemical agent is to determine its phenol coefficient. This is simply a comparison of the killing action of the compound to that of phenol under the same conditions. Phenol ("carbolic acid") is a toxic compound and is not as widely used today, but it was historically defined "yardstick" by which to evaluate other disinfectants. In this exercise, we will monitor the viability of a culture to determine the phenol coefficient of a test compound. importantin the development of aseptic surgical techniques, and provides a well- Today's phenol coefficient demonstration was done by mixing the chemical being tested with Staphylococcus aureus. At the listed times, a loopful of the mixture was transferred into a sterile nutrient broth tube, and incubated. To evaluate these tubes, look for growth in the tube. ANY cloudiness growth. Be sure to look and see if any of the growth has settled to the bottom of the tube. On your lab report, record each test tube as (+) for growth or (- for no growth. Chemotherapeutic agents or antibiotics are antimicrobial compounds that can be safely absorbed or taken internally. The effectiveness of antibiotics can be evaluated two different ways. The first method, the tube dilution, consists of a serial dilution of the antibiotic to which a standard amount of bacteria is added to each tube. After incubation, the highest dilution of antibiotic with no growth is the minimum inhibitory concentration (MIC). MIC is the exact value of the smallest amount of antibiotic that kills/inhibits the MOs. The effectiveness of an antibiotic is more conveniently measured by the Kirby-Bauer agar diffusion method. A micro-organism is first spread over the surface of a petri plate. Paper discs impregnated with various antibiotics are then placed on the surface of the agar. During incubation, the antibiotic diffuses from the disk, forming a concentration gradient in the plate itself: high concentratio area. If the anti appear around the disk as a confluent law The size of this zone roug species since diffusion, the size of the inoculum, the growth stage of the h zones of inhibition are measured and compared to n near the disk and decreasing concentration out into the surrounding biotic inhibits the organism, a clear zone of inhibition (area of no growth) will n of cells develops everywhere else hly indicates the effectiveness of that antibiotic against that bacterial on the plate zone size can also be affected by many different factors, including the rate of acteria... The diameters of the a standard chart to determine if this bacteria is sensitive, intermediate, or resistant to aExplanation / Answer
1. Bacteriostatic treatment aims to inhibit the growth of bacteria wherein bactericidal treatment actually kills the bacteria.
2. Lysol is a diluted solution of methylphenol. Hence phenol is more toxic than lysol.
3. Yes. Agar diffusion of drug gives the value of MIC. At MIC, drug inhibits microorganisms completely.
4. Disinfectant are toxic to the host cells where as antibiotics act only on microorganisms. Some disinfectant even cause cancer.
5. Specificity of antibiotic depends on microorganisms. Some act only on gram positive while others act on gram negative bacteria. Hence it is necessary to know the pathogen.
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