Unknown Lab Report Essay

The purpose of this lab is to isolate a bacterial population from the normal throat flora. A streak plate method will be used to obtain a pure culture of a Gram positive coccus genus of bacteria. Several biochemical tests will be performed to aid in the identification of this unknown bacterium. Biochemical tests are a series of tests used to identify certain bacterium The various tests that are used in this lab are the catalase test, oxidase test, blood hemolytic test, MSA, blood agar, and PEA/ab sens test.

A known Gram positive coccus bacteria will be used alongside an isolated Gram positive unknown bacteria for comparison to aid in the ability to identify the isolated organism to the genus level. There are many reasons for identifying an unknown bacterium. Some reasons to identify an unknown bacterium could help one determine if the unknown could cause illness in living things or help make antibiotics to kill bacteria that can cause some illnesses. Bacteria are necessary for the maintenance of human health. An important function of our normal flora is to protect us from highly pathogenic organisms.

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Some pathogenic bacteria also pose a major health threat by causing diseases. Staining techniques are going to be performed in this lab to determine if the unknown bacteria is indeed Gram positive or Gram negative. The type of bacteria being investigated in this lab is Gram positive bacteria. Gram positive bacteria are those that are stained dark blue or violet by Gram staining. Gram positive organisms are able to retain the crystal violet stain because of the high amount of peptidoglycan in the cell wall. (Wikipedia).

It is important to know whether the unknown bacteria is Gram positive or Gram negative because Gram positive bacteria can be killed with antibiotics. Doctors are also able to determine which type of antibiotic to use to kill the bacteria that can be causing a significant health threat in their patients. Not all Gram positive bacteria are pathogens (disease causing microbes), some are natural flora and are beneficial to the human body. Many normal flora provide direct benefits, such as making vitamins, aiding digestion, and can help prevent pathogens from easily invading the body and causing illness.

Unknown Lab Report Essay

Unknown Lab Report Dr. Nathan Cahoone Microbiology 204 December 9, 2010 Introduction There are many reasons for knowing the identity of microorganisms. The study and test was done by applying all of the methods that have been learned so far in the microbiology laboratory class for the identification of an unknown bacterium which I was using unknown #25. Results

Unknown #25 had the following morphology on a streak plate: medium sized butyrous cream colored colony. Gram-staining was utilized as a first step to differentiate between gram-positive and gram-negative. After determining that it was a Gram negative single bacillus, biochemical tests performed and their purpose and results are shown in table and flow chart form. Table 1: biochemical Test Results Test| Purpose| Reagents| Observations| Results|

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Gram stain| To determine the Gram reaction of the bacterium| Crystal violet, Iodine, Alcohol, Sarasin| Pink rod| Gram-negative rods| Carbohydrate (Glucose) fermentation| To determine the ability of a bacterium to fremnet a carbohydrate, make acid or gas| Durham tube| Color change from red to yellow, bubble in Durham tube| Positive carbohydrate fermentation, acid production and gas production| Tryptophan digestion| To determine the ability of an organism to split indole from tryptophan| Kovac’s drop added to tryptone broth| Kind of colorless and list green ring at top of broth| Negative tryptophan digestion| Cystine digestion| To determine the ability of an organism to catabolize certain amino acids| Iron ions| Color didn’t changed remaind creamy| Negative cystine digestion| Citrate Utilization| To determine the organism is able to utilize citrate as a carbon source| Citrate slant (green) & Bromthymol blue| Color changed from green to deep blue| Positive for citrate utilization| Urea digestion| To determine the ability of an organism to catabolize ammonia| Phenolmed| Color didn’t change stayed bright orange| Negative for urea digestion| Flowchart Unknown# 25 Gram stain Gram-negative Rod Glucose fermentation (positive) Positive Negative Escherichia coli Pseudomonas aeruginosa Enterobacter aerogenes Pseudomonas fluorescens Salmonella enteritidis Serratia marcescens Proteus vulgaris

Gelatine drolysis (positive) Positive Negative Serratia marcescens Escherichia coli Proteus vulgaris Enterobacter aerogenes Salmonella enteritidis Motility test (negative) Proteus vulgaris Unknown# 3 – Proteus vulgaris Discussion/ Conclusion After several differential tests, it was concluded that unknown# 25 was Proteus vulgaris. After performing the Gram stain to determine that the unknown was a Gram negative rod, the organism was grown on slant for use in inoculating the rest of the biochemical tests. All of the biochemical tests worked well except for the motility, cysteine digestion and urea digestion.

According to chart it should be positive but because of the human error, not appropriate temperature, and too old culture, etc it gave a false negative result. For example: the culture that I used it might be too old, or when I was inoculating the culture to the urea it might be hot, leaded to kill the bacterium . That is why I got false negative result. Other than this everything (data) was great and into the conclusion the unknown was Proteus vulgaris. P. vulgaris is in the Enterobacteriaceae family and opportunistic pathogen of humans. Colonies of Proteus inhabits the intestinal tracts of humans and animals. It can be found in soil, water and fecal matter.

This genus, species of bacteria is implicated in many infections of the urinary tract and in wounds infections. P. vulgaris had really interesting growth on agar plates. The cells from very thin of bacteria on the surface by swarming, and interspersed with periods and the colony has a distinct zonation or rigns of growth at 37C but the true is they grows best at 25C according to the broth grow. So I think my unknown was Proteus vulgaris. Reference 1. Community College of Denver. Microbiology Laboratory Manual, Denver, 2010 2. Tortora, Funke, Cace, Microbiology and Introduction, 10 Th editions. San Francisco: Pearson Benjamin Cummings, 2010 3. http://en. citizendium. org/wiki/Proteus_vulgaris

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