Lab 7 Report Sheet

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Tallahassee Community College *

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2010

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Biology

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Feb 20, 2024

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doc

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Name(s): Nicole Linebaugh Lab 7 Report : DIFFERENTIAL AND OR SELECTIVE MEDIA & THE KIRBY-BAUER: PROCEDURE FOR TESTING ANTIBIOTIC SENSITIVITY 1) Record your observation of grown cultures: Test performed S. aureus E.coli Hemolysis test Gamma Hamonic reaction No Lactose formation; no bacteria McConkey test No color change No color change Mannitol salt test Nonpathogenic, no color change, clear Color change to bright pink to yellow EMB test Nonfermented when incubated with EMB. Clear culture. No color changes. Antibiotics used and conc. S. aureus E.coli Ampicillin S I R / IZ(mm)= 16mm S I R / IZ(mm)= 4mm Clindamycin S I R / IZ(mm)= 10mm S I R / IZ(mm)= 0mm Gentamycin S I R / IZ(mm)= 9mm S I R / IZ(mm)= 9mm Penicillin S I R / IZ(mm)=17mm S I R / IZ(mm)= 0mm (S:sensitive, I:intermediate, R:resistant, IZ(mm):inhibition zone/diameter of growth ) 2) Did you have the same results with your lab partners if they worked on the same bacterial culture? What reasons you might think contributed to the differences: Yes, my results were the same as my lab partner, Elise. The reasons the results were all the same were because of good technique and no contamination was found. 3) What is the purpose of using blood agar plate test? What caused hemolysis? Distinguish the differences between hemolysis

The blood agar plate test serves the purpose of distinguishing bacteria by their capacity to induce hemolysis, which is the breaking down of red blood cells. Various patterns of hemolysis can be discerned, including alpha/partial hemolysis, beta/complete hemolysis, or gamma/no hemolysis. This examination aids in the recognition of specific bacterial species and offers insights into their potential for causing disease. 4) What is the phenomenon that contributes to the positive results in McConkey test? What is the purpose of this test? The presence of positive outcomes in the McConkey test can be attributed to the breakdown of lactose by lactose-fermenting bacteria, leading to the formation of acidic compounds. This acid production results in a decrease in pH, triggering a color change in the indicator present in the medium. The primary objective of conducting the McConkey test is to distinguish between bacteria that are capable of fermenting lactose and those that are not, with specific emphasis on identifying and differentiating between members belonging to the Enterobacteriaceae family. 5) What is the purpose of using a candle jar? The candle jar serves the purpose of establishing a microaerophilic or anaerobic setting suitable for bacteria that thrive in low oxygen levels or are naturally anaerobic. The technique involves sealing a container and introducing a lit candle alongside agar plates. By consuming oxygen and generating carbon dioxide, the lit candle generates the desired environment for targeted bacterial growth conditions. 6) For an accurate reading, your plates should be observed from visualization of bacterial growth, the appearance of colonies, and the detection of inhibition zones surrounding antibiotic discs, it is necessary to observe the samples from both an overhead and a bottom perspective. 7) If you want to identify a strain of pathogenic staphylococci, which type(s) of above media should you use? Why? Staphylococcus aureus, the most pathogenic strain of Staphylococci, can be distinguished from less virulent coagulase-negative Staphylococcus species through a coagulase test. This test can be performed using either a slide or tube method. S. aureus appears as golden yellow colonies on nutrient agar. On blood agar, it forms small pinhead-sized colonies that exhibit complete hemolysis (beta hemolysis). Mannitol Salt agar is the best selective media for S. aureus, as it causes a color change from pink to yellow when the bacteria ferment mannitol. S. aureus colonies on potassium tellurite agar appear black due to the reduction of tellurite in the medium. Pink colonies are observed on phenolphthalein phosphate agar, indicating the presence of phosphatase activity in S. aureus. 8) The theoretical basis of the Kirby-Bauer technique for testing antibiotic sensitivity can be used to identify an unknown strain of bacteria: a) True

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