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Unknown Lab Report
By knowing what diseases are caused by different types of bacteria and their modes of action, healthcare workers can treat patients with the proper medication. Also, healthcare workers can help prevent the spread of disease by knowing how different types of bacteria are passed. The community benefits from studies on bacteria because it can advise them on how to keep their families healthy.
Materials and Methods
An unknown mixed culture numbered 108 was given by the teacher. Several mediums were used to isolate two pure cultures and determine the two types of bacteria.
A nutrient agar plate was streaked with the unknown culture and incubated at 37 degrees Celsius. Gram stains were performed on two isolated colonies on the nutrient agar plate. The slides showed both Gram-negative and Gram positive bacteria mixed together. Another nutrient agar plate was streaked to further isolate the two different types of bacteria. The nutrient agar plate was incubated at 37 degrees Celsius. Gram stains were performed on two of the isolated colonies. Again, the slides showed both Gram negative and Gram positive bacteria mixed together on the slides. Since the isolation technique did not work, one mannitol salt agar plate was streaked with the initial unknown culture to allow the growth of only the Gram positive bacterium. The plate was incubated at 37 degrees Celsius. The mannitol salt agar plate was observed for isolated colonies. A nutrient agar plate was streaked with one isolated colony from the mannitol salt agar plate to insure a pure Gram positive colony. The nutrient agar plate was incubated at 37 degrees Celsius. A Gram stain was performed on one isolated colony. The slide showed only one type of bacterium which was a Gram positive rod. So, an oxidase test was done from the isolated colony and showed no color change which indicates a negative result. The correct gram positive bacterium was identified. Since the Gram positive bacterium was identified, one desoxycholate agar plate was streaked from the initial unknown culture to allow growth of only the Gram negative bacterium. The desoxycholate agar plate was incubated at 37 degrees Celsius. A Gram stain was performed from an isolated colony and the slide showed only a gram negative rod bacterium. A simmons citrate agar and a urea broth were inoculated from the isolated colony. The mediums were incubated at 37 degrees Celsius. The simmons citrate agar turned blue which determined a positive result. The urea test had no color change which determined a negative result. An oxidase test was done and showed a negative result. The incorrect bacterium was identified, so a pure Gram negative culture was given by the teacher. A urea broth and a simmons citrate agar was inoculated from the pure culture and incubated at 37 degrees Celsius. The urea broth turned pink which indicates a positive result. The simmons citrate turned blue which indicates a positive result. The correct bacterium was identified.
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The following tests were performed to determine the unknown:
- Oxidase test
- Simmons citrate
Gram positive rod
Oxidase test (negative)
Bacillus subtilis Bacillus cereus
Unknown 108: Bacillus subtilis
Gram negative rod
Simmons citrate (positive)
Klebsiella pneumoniae Escherichia coli
Enterobacter aerogenes Proteus vulgaris
Urea test (positive)
Unknown 108: Klebsiella pneumoniae
After performing Gram stains, a gram positive rod was observed. According to the unknown chart provided by the teacher, the bacterium was either Bacillus cereus or Bacillus subtilis. An oxidase test was done and there was no color change to the bacterium which indicates a negative result. The oxidase test concluded that the bacterium was Bacillus subtilis. This was the correct identification of the bacterium. After performing Gram stains, a Gram negative rod was observed. A simmons citrate test was done and it showed a positive result. Also, a urea test was done and it showed up negative. The urea test gave a false negative result. The first round of tests on the Gram negative rod concluded that the bacterium was Enterobacter aerogenes. This was the incorrect bacterium. A pure Gram negative rod culture was given by the teacher. A simmons citrate and urea test were performed on the pure culture. The simmons citrate turned blue which indicates a positive result. The urea test turned pink which indicates a positive result. According to the unknown chart, it was concluded that the bacterium was Klebsiella pneumoniae. This was the correct identification of the bacterium.
Klebsiella pneumoniae is a Gram negative rod bacterium that can form a capsule. It is found in the normal flora of GI tracts in humans. K. pneumoniae can become pathogenic in patients whose immune systems are compromised. K. pneumoniae can cause nosocomial urinary tract infections and pneumonia. In immunocompromised patients, death is possible (Klebsiella). For a person (patient) to get the K. pneumoniae bacteria, they have to have direct contact with another person. K. pneumoniae is not able to be contacted through the air (Centers for Disease). Healthcare workers can help to decrease the spread of K. pneumoniae by washing their hands before and after taking care of a patient.
Centers for Disease Control and Prevention. Klebsiella pneumonia in Healthcare Settings, 2012.
Web. 3rd Dec. 2012. https://www.cdc.gov/
Klebsiella pneumoniae. 2011. Web. 3rd Dec. 2012. https://klebsiella-pneumoniae.org/
McDonald, V, et al. Lab Manual for General Microbiology: BIO 203.