Identification of an Unknown Pathogen and Recommended Treatment Hussien Mohamed MCB 3020L, SEC.008 UNKNOWN #10
Mohamed 1 Summary The purpose of this experiment was to use the various test and laboratory techniques learned throughout the semester to identify an unknown pathogen and to propose a recommended treatment. The series of tests needed to identify the unknown was established by the cell wall composition of the unknown bacterium. The unknown bacterium was determined to be Gram-negative through the Gram stain and KOH test. To complete identification of the unknown bacterium, MacConkey (Mac) and Salmonella-Shigella (SS) plates, as well as Triple Sugar Iron (TSI) and Citrate slants were inoculated with the unknown bacteria. Isolates produced bright pink colonies on the Mac agar and pink-red colonies on the SS agar. The TSI slant had a result of A/A/+/-, which indicates an acidic slant and butt, visible gas production, and no H 2 S gas production. The citrate slant appeared green. A Kirby-Bauer test was also conducted to determine the susceptibility and resistance of the unknown bacteria to three antibiotics: Neomycin, Polymyxin B, and Tetracycline. The unknown was susceptible to all three antibiotics. The unknown bacterium was conclusively determined to be Escherichia coli upon analysis of the results . Although E. coli was determined to be susceptible to all three antibiotics, Polymyxin B was chosen as the recommended treatment because the bacterium exhibited the greatest susceptibility to this antibiotic. Materials and Methods All methods were adapted from the Microbiology Lab Manual (CMMB, 2017). The Gram Stain and the KOH Test
Mohamed 2 The first test conducted to determine the identity of the unknown bacterium was the Gram stain. To begin, a bacterial smear was prepared by placing a drop of water and a small amount of the unknown sample on a glass slide using an inoculating loop. The slide was then heat-fixed by passing the slide through a Bunsen burner flame a few times. The smear was covered with crystal violet for one minute and then rinsed with water. The smear was then covered with Gram’s iodine for one minute and rinsed with water again. The smear was decolorized by adding 95% ethanol drop-wise. After rinsing with water a third time, the smear was covered with the counterstain, safranin, for one minute. The smear was rinsed with water a final time and was blot dried. The slide was examined under oil immersion, and the color and shape of the bacteria was recorded. The KOH test was used to verify the results of the Gram stain. A small amount of the unknown sample was placed on a glass slide and a drop of 3% KOH was added to it. The slide was left to sit for one minute. A toothpick was used to mix the fluid so that the viscosity could be determined. Gram-negative bacteria appear as viscous and stringy and Gram-positive bacteria appear as cloudy.
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