A new antibiotic and a new antiseptic have been discovered. Both agents appear t

Question

A new antibiotic and a new antiseptic have been discovered. Both agents appear to be effective against most gram positive and gram negative bacteria. However, the level of effectiveness has not been properly determined. Describe how you would determine the effectiveness of both agents experimentally. How would you rate the effectiveness of the new antiseptic against phenol using the Phenol Coefficient Test? (Search for information regarding the Phenol Coefficient Test and cite your references appropriately).

Explanation / Answer

An antibiotic is effective against a specific spectrum of germs as long as these germs do not develop or acquire resistance to it. Antibiotics by definition treat certain bacterial infections . Before bacteria can multiply and cause symptoms, the body's immune system can usually kill them. Our white blood cells attack harmful bacteria and, even if symptoms do occur, our immune system can usually cope and fight off the infection.

The effectiveness of various chemical disinfectants is reflected in the terms used to describe them. Chemical disinfectants are grouped by the power of their activity, with each category reflecting the types of microbes and viruses its component disinfectants are effective against.

The effectiveness of a disinfectant or antiseptic can be determined in a number of ways. Historically, a chemical agent’s effectiveness was often compared with that of phenol, the first chemical agent used by Joseph Lister. In 1903, British chemists Samuel Rideal (1863–1929) and J. T. Ainslie Walker (1868–1930) established a protocol to compare the effectiveness of a variety of chemicals with that of phenol, using as their test organisms Staphylococcus aureus (a gram-positive bacterium) and Salmonella enterica serovar Typhi (a gram-negative bacterium). They exposed the test bacteria to the antimicrobial chemical solutions diluted in water for 7.5 minutes. They then calculated a phenol coefficient for each chemical for each of the two bacteria tested. A phenol coefficient of 1.0 means that the chemical agent has about the same level of effectiveness as phenol. A chemical agent with a phenol coefficient of less than 1.0 is less effective than phenol. An example is formalin, with phenol coefficients of 0.3 (S. aureus) and 0.7 (S. enterica serovar Typhi). A chemical agent with a phenol coefficient greater than 1.0 is more effective than phenol, such as chloramine, with phenol coefficients of 133 and 100, respectively. Although the phenol coefficient was once a useful measure of effectiveness, it is no longer commonly used because the conditions and organisms used were arbitrarily chosen.

The Phenol coefficient, is now largely of historical interest, although the principles upon which it is based are still used.It is a measure of the bactericidal activity of a chemical compound in relation to phenol. When listed numerically, the figure expressing the disinfecting power of a substance by relating it to the disinfecting power of phenol may be a function of the standardized test performed.To calculate phenol coefficient, the concentration of phenol at which the compound kills the test organism in 10 minutes, but not in 5 minutes, is divided by the concentration of the test compound that kills the organism under the same conditions (or, probably more common, dividing the dilution factor at which the tested substance shows activity by the dilution factor at which phenol shows comparable activity). The Rideal–Walker test was widely used, but the test conditions chosen were unrealistic, and impossibly high values for the coefficient were claimed by disinfectant manufacturers.

Phenol coefficient may be defined as the killing power of germicide or an antimicrobial agent towards a test organism compared to that of phenol under identical conditions. It is the ratio of the higher dilation of disinfectant killing the organism in 10min. but not in 5min, to the of the highest dilution of phenol showing the same result.

Materials: - 24 hrs. Broth culture

Sterile test tube (10)

Platinum 100p

Nutrient broth (10ml per tube)

Distilled water.

Sterile diln flask.

Sterile 5 and 10ml graduated pipettes.

Various dilution of phenol.

Various dilution of disinfectant under test.

Procedure:-

Place 5ml of various dilutions of phenol and disinfectant under test into sterile test tube Label them from 1 to 10, place 0.5ml of broth culture of test organism into tubes no1, shake to distribute the organism and at 30sec. internal thereafter add 0.5ml of culture of test organism in to tubes no1, shake to distribute the organism and at 30 sec. interval thereafter add 0.5ml of culture to the remaining tubes containing various dilutions. When tube no.10 is inoculated 41/2 min will be passed 30 second later proceeding as follows.

Place one standard loopful from tube no1 to the tube of broth and at 30sec. internal thereafter transfer a loopful of each successive disinfecting mix. This will give 3 series of inoculation to a fresh tube of broth until 3 transfers have been made from each disinfecting mix. This will give 3 series of inoculation in to broth after 5,10 and 15 min exposure of test organisms, through various concentrations. of disinfectant. In cubit broth tubes at 370c for 48hrs. Record in a tubular from presence or absence of growth

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