Bacteria Lab Report

Topics: Bacteria, Microbiology, Gram-negative bacteria Pages: 7 (1734 words) Published: November 9, 2014
THE DETERMINATION OF ANTIBIOTIC SUSCEPTIBILITY WITH THE UTILIZATION OF BAUER-KIRBY DISK FUSION METHOD

INTRODUCTION:

The most common way of alleviating the specific symptoms arrived from diseases is to ingest antimicrobial drugs. Chemotherapeutical antimicrobial agents are chemical compounds intended to inhibit or kill rapidly dividing microorganisms. In order to derive an antimicrobial drug, different chemical compounds must be synthetically formed. Among these specific chemical compounds is a compound famously known as the antibiotic. The antibiotic is classified as an antimicrobial drug because it's a chemical that is produced by either a bacterium or fungus, which has the ability to regulate the growth of other microorganisms.

The validity of antibiotics as a category of antimicrobial drugs was determined by a method that was developed by Kirby and Bauer, and standardized by the World Health Organization in 1961 to ensure reliable results. The Bauer-Kirby method was highly suggested by the U.S. Food and Drug Administration to determine the antimicrobial disk susceptibility. (Liberman et al., 1966) Therefore, extreme care is required to meet to the standards. To begin meeting the standards, a Mueller-Hinton agar is used for the bacteria culture. The standard Mueller-Hinton agar usually requires a pH between 7.2 and 7.4, which is then poured to a depth of 4mm in either 150 mm or 100mm Petri dishes. The petri dish is then heavily inoculated with a specific bacteria and different paper disks that contain different antibiotics to examine. With the disks on the inoculated petri dish, the petri dish must be sealed and placed into an incubator at an exact temperature of 37°C for 24 hours and allow the bacteria to grow. Within 24 hours, the bacteria must be put into a refrigerator with an estimated temperature of 4.4°C to prevent overproduction of bacteria. By examining the results of the incubation of bacteria, the zone of inhibition, which is the area without bacterial growth that surrounds the antimicrobial disk, can determine how effective the antibiotics were against the bacteria. Depending on the length of the radius of the clear region around the paper disk, an estimated measure from the edge of the paper disk of 1-2 cm can determine how powerful the antibiotics were. Some of the bacteria may show small or no zones of inhibition if their growth was completely resistant to the antibiotic. Though this may be the case, the more sensitive cultures will be utilized efficiently to counter the different diseases that are brought on by specific bacterium.

With the experiment explained and discussed, a group of two students including I tested one antibiotic against three different pathogens. Erythromycin, a compound produced by a strain of Saccharopolyspora erythraea that is categorized as a macrolide group of antibiotics. This antibiotic is an extremely useful antibiotic often prescribed to patients who are allergic to penicillin. Erythromycin inhibits the synthesis of specific proteins that is essential to bacteria reproduction. (Weisblum, 1995) With the inhibition of protein synthesis, erythromycin does not necessarily kill the bacteria, but leaves them unable to replicate. The remaining bacteria are incapable of surviving and are destroyed by the immune system.

The three different pathogens, _Escherichia coli, Shigella flexneri, and Staphylococcus aureus_ were exposed by Erythromycin and the effects were examined.

_Escherichia coli (E. coli),_ a prokaryote with one circular chromosome composed of monocistronic (single genes) and polycistronic genes is a Gram-negative, rod shaped, bacterium that essentially lives in the intestine of warm-blooded organisms. The cell structure of an _E. coli_ possesses a cell wall that is constructed by lipopolysaccharides, a peptidoglycan layer, and a cytoplasmic membrane. _E. coli_ can cause severe infections to animals by ascending infections of the urethra and kidneys, which...

References: Boyle, V.D., Fancher, E.M., Jr. Ross, W.R. (1973). Rapid, Modified Kirby-Bauer Susceptibility Test with Single, High-Concentration Antimicrobial Disks. _Antimicrobial Agents and Chemotherapy,_ 3(3): 418-424
Liberman, F.D., Robertson, G.R. (1975). Evaluation of a Rapid Bauer-Kirby Antibiotic Susceptibility Determination, _Antimicrobial Agents and Chemotherapy,_ 7(3): 250-255
Bauer, A.W., Kirby W.M., Sherris, J.C., Turck, M. (1966). Antibiotic susceptibility testing by a standardized single disk method, _Am J Clin Pathol,_ 45(4): 493-496
Boyle, V.J., Fancher M.E., Ross R.W., Jr Rapid. (1973) Modified Kirby-Bauer Susceptibility Test With Single, High-Concentration Antimicrobial Disks. _Antimicrobial Agents and Chemotherapy_, 3(3): 418-424.
Weisblum, Bernard (1995). Erythromycin Resistance by Ribosome Modification.
_Antimicrobial Agents and Chemotherapy_, Mar. 1995, 577-585.
Chan, V.L., Sherman M.P., Bourke, Billy (2006) Bacterial genomes and infectious diseases, _Humana Press._
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