The purpose to this lab was to isolate and identify two unknown bacteria from a mixed culture provided to us. This study was done by applying all of the methods that have been instructed on thus far in microbiology laboratory class. Each test performed, provided us with some key information about the unknown microbes in question . The identification of unknown bacteria is a time honored part of microbiology courses.
It will challenge knowledge and skill in performing laboratory techniques, ability to critically evaluate the information obtained from these techniques, and ability to effectively communicate the information.
There are many reasons for knowing the identity of microorganisms. The reasons range from the knowing the causative agent of a disease in a patient, so as to know how it can be treated, to knowing the correct microorganism to be used for making certain antibiotics. This study 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.
II. Results Unknown A a. The unknown is a gram negative bacilli Upon performing a gram stain on a colony from a streak of the unknown bacteria, at 100x, the bacteria stains negative for the gram stain. In addition, the structure of the bacteria is bacilli. b. The unknown is a facultative anaerobe A small amount of bacteria was added to a tube of fluid thioglygollate media, which permits the of a wide variety of bacteria and also allows the determination of the oxygen requirements of an organism.
c. The unknown is nonmotile The media was inoculated with a single stab to the center of the tube and incubated.
After incubation, the growth was restricted to the stab line, the bacteria is nonmotile. d. The unknown is no capsule formed The bacteria was removed from a single loopful of broth from the tube and streak it into blood agar plate using streak plate method. Incubated for about 24 hours in 37 degrees Celsius. The colony did not show a mucoid appearance and was not sticky. The colony is no capsule formed. e. The unknown is mannitol positive The bacteria was inoculated into a broth that containing the test sugar and incubated. A bright yellow color indicates the production of acid is positive.
Production of a gas was determined with Durham tube, which is trapped at the top of the Durham tube and appeared as a bubble. * Acid ( + ) and gas ( + ) f. The unknown is lactose positive The bacteria was inoculated into a broth that containing sugar. Acid was produced as evidenced by the yellow color, and gas was made. Acid ( + ) and gas ( – ) III. Conclusion After several differential tests, it was concluded that unknown A was Shigella sonnei. After performing gram stain to determine that the unknown was a gram negative bacilli, the organism was grown on a TSA slant for use in inoculating the rest of the biochemical test.
All of the biochemical tests worked well except for the lactose and sucrose, its produced acid and gas. In Shigella sonnei, there is no gas production from lactose and sucrose. The wrong interpretation of data especially from carbohydrate fermentation was challenging. The color that been produced was hard to distinguish because the yellow orange and red was look similar. III. Results A. The unknown is a Gram negative coccobacillus Upon performing a gram stain on a colony from a streak of the unknown bacteria, at 100X, the bacteria stains negative for the Gram stain. In ddition, the structure of the bacteria is coccobacillus. B.
The unknown is catalase positive A smear of bacterial culture was placed on a slide, and upon addition of a 3% solution of Hydrogen Peroxide, produced white bubbles. This is indicative of catalase activity and thus the unknown is catalase positive. C. The unknown is not able to ferment lactose A small amount of bacteria was added to a tube of Phenol Red Lactose, where the Phenol Red pH indicator will change upon the fermentation of lactose. After culturing, the tube did not change to yellow, and stayed red, indicating the inability to ferment lactose.