Unknown Bacteria Lab Report- Microbio PDF

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Unknown Bacteria Lab Report Intro Clinical laboratories need be able to test and identify any dangers related to the bacteria. It is important to inform physicians of the identification characteristics of the bacteria in order for the physician to start the appropriate treatment as soon as possible. In the case of an outbreak, identification of characteristics or even the specific type of the bacteria gives physicians the ability to source, control, and prevent the recurrence of the disease. Many different tests are available to be used to identify the species of bacteria including, but not limited to, specific stain techniques, colony morphology, enzymatic tests, and biochemical tests (Baron, 1996, Reller et al., 2001). The purpose of this lab was to use different techniques to identify two unknown species of bacteria, one being gram-negative and the other gram positive.

Methods The gram stain was used to indicate whether each bacterium was gram-positive or gramnegative. It was also used to identify morphology and grouping of the species. The citrate utilization test indicates the use of citrate as a carbon source. If the citrate is being utilized, basic conditions are produced. The medium will turn blue in basic conditions, pH 7.6 or greater. Acidic conditions, pH below 6.9, turns the medium green. The EMB plate is a differential and selective medium. It does not allow gram positive bacteria to grow and indicates lactose fermentation by the color of the colony. A green color indicates vigorous fermentation. A pink/purple color indicates slow-moderate fermentation. No color indicates no fermentation in the colony. The urease test indicates the degradation of urea. A change in the color to red indicates urea degradation. A negative result remains a yellow-orange color.

The catalase test differentiates between catalase and peroxidase producing bacteria. These are produced in order to minimize reactive oxygen species and make the environment survivable. Aerobic bacteria generally produce one or the other. Catalase is an enzyme that breaks down H2O2 into water and oxygen gas. The hemolytic activity test uses a blood enriched medium to indicate hemolytic activity of bacteria. Hemolytic bacteria able to degrade the proteins and red blood cells for metabolic use. Beta hemolysis, complete degradation of red blood cells, will show a halo around the colony. Gamma hemolysis, no degradation, will not show a halo. The bile esculin test is selective and differential. Only organism able to live in the presence of bile will grow on the bile enriched plate. Bacteria that are able to esculetin to utilize the esculin will turn black due to the reaction between ferric citrate and esculetin.

Results Morphology Streptococcus Morphology Singular Rod

Gram-positive Hemolytic Beta Gram-negative EMB Urease +++, green sheen Catalase -

Bile- esculin Citrate -

For the gram-positive cocci species, the tests allowed the identification of a bacteria that is biochemically unable to produce catalase, unable to live in the presence of bile, and highly able to lyse red blood cells. These results directly correlate with the Streptococcus pyogenes species. For the gram-negative rod species, the bacteria did not produce urease and was unable to utilize citrate but was able to vigorously utilize lactose. These results correlate with the Escherichia coli species.

Discussion When observing the gram-positive species, Micrococcus luteus was eliminated because the morphology did not show tetrad formation. When testing, the catalase test was used and indicated that the bacteria was not a staphylococcus species. The hemolytic test was used to differentiate between Streptococcus pyogenes and Enterococcus faecalis. E. faecalis was eliminated and S. pyogenes was the only possible species left. The bile esculin test was used to reinforce the end result. When testing the gram-negative species, an EMB plate was used to indicate lactose utilization and Proteus Vulgaris was eliminated. The citrate test was used to differentiate Escherichia coli from the other species. Urease was used to reinforce the end result. The tests were used and chosen based on the given list of possible bacteria. Everything worked as it should, and the two bacterial species were identified. This method allows for basic differentiation of bacterial species but does not express possible variations within species such as antibiotic resistance. For stronger classification, this method can be strengthened with more tests.

References Baron EJ. Classification. In: Baron S, editor. Medical Microbiology. 4th edition. Galveston (TX): University of Texas Medical Branch at Galveston; 1996. Chapter 3. Available from: https://www.ncbi.nlm.nih.gov/books/NBK8406/

Reller, L.,Barth, Weinstein, M.,P., Peterson, L.,R., Hamilton, J.,D., Baron, E.,Jo, Tompkins, L.,S., . . . Thomson, Jr. ,Richard,B. (2001). Role of clinical microbiology laboratories in the management and control of infectious diseases and the delivery of health care. Clinical Infectious Diseases, 32(4), 605-610. 10.1086/318725 [doi]...