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Kylie Wimbish BIO 351- 505 20 October 2023 Soil and Water Results and Conclusions Table 1. Soil Microbial Counts Organism Data Collected Colonies counted (CFU) Original sample volume (mL) Cell density per mL (CFU/mL) Cell density per gram soil (CFU/g) Actinomycetes (GYE) 47 1.0 x 10 ⁴⁻ 4.7 x 10⁵ 4.7 x 10⁶ Fungi (SDA) 59 1.0 x 10 ³⁻ 5.9 x 10⁴ 5.9 x 10⁵ Bacteria (TSA) 113 1.0 x 10 ⁴⁻ 1.13 x 10⁶ 1.13 x 10⁷ Table 2. Presumptive Test (Lactose Tryptose Broth) Group Data Collected Volume of water (mL) added to each Lactose Broth Total number of Lactose Broth inoculated Number of Lactose Broths with gas production Group A 10 5 5 Group B 1 5 4 Group C 0.1 5 3 Table 3. Confirmed Test with Brilliant Green Lactose Broth (BGLB) Group Data Collected Volume of water (uL) transferred from each Lactose Broth to BGLB Total number of BGLB Broths inoculated Number of BGLB Broths with gas production Group A 20 0 0 Group B 20 2 1 Group C 20 3 0 Results
At the completion of the soil microbial count experiment over a 2-day period, it was found that the tryptic soy agar (TSA) sample used primarily to grow bacteria had large growth within the 10 ³ dilution, the sabouraud dextrose agar (SDA) sample used to grow fungi had⁻ growth within the 10 ² dilution, and finally the Glucose Yeast Extract Agar (GYE) sample used⁻ to grow actinomycetes showed growth within the 10 ³ dilution. The original sample volume of⁻ actinomycetes for example was calculated by multiplying the dilution factor with the most bacterial growth by 0.1 mL. The cell density per mL value of actinomycetes was calculated by dividing the original sample volume by the number of colonies counted. Finally the cell density per gram of soil of actinomycetes was calculated by multiplying the cell density per mL by 10. All other values were calculated using the same formulas described above (1). During the presumptive test, dilutions from the water samples performed and analyzed in the above tables were added to lactose tryptose broth fermentation tubes and then analyzed for gas production. Using the results obtained from our tubes based on positive and negative gas production and the Most Probable Number Index table given it was found that the most probable number was 280 coliforms/100 mL of water (2). The results of the presumptive test were used in the above experiment known as the confirmed test where 5 of the tubes with the least amount of gas production were inoculated into Brilliant Green Lactose Broth cultures. Only one of these tubes was found positive for gas production after 48 hours and using the MPN Index table given, it was found that the most probable number index was 2 coliforms/100mL of water (2). Using the single positive gas production tube from the confirmed test experiment an Eosin Methylene Blue Plate (EMB) and a Hektoen Enteric Agar Plate (HE) were streaked in order to determine the presence or absence of E.coli which would have appeared as a green
selective and differential. Based on the results of the tubes that tested positive for gas production it was determined that the most probable number index was 280 coliforms per 100 mL of water according to the table given (2). Of these dilutions collected, the five lowest dilutions with positive gas production tests were then inoculated into Brilliant Green Lactose Broth tubes; this process makes up the confirmed test used to ensure the accuracy of the previous test (2). The final test of this experiment known as the complete tests took the positive gas production tubes from the completed tests and streaks them across an Eosin Methylene Blue Plate (EMB) and a Hektoen Enteric Agar Plate (HE) (3). The results of this experiment confirm the presence of coliforms on the EMB plate signaled by a purple to black color change while the HE plate further confirmed this statement by a pink to orange color change indicating pathogenic coliforms (3). The confirmation of these results through a series of tests performed allows these results to be labeled as reliable. Works Cited
- Janes D, Moyes R, Longcrier C, Basile L. 2023. Soil Microbial Count. BIOL 351 Week 5 Lab Manual. Texas A&M University. College Station, TX. Biology 351. 2023. Week 5 PowerPoint. Texas A&M University. College Station, TX.
- Janes D, Moyes R, Longcrier C, Basile L. 2023. Microbiology of Water. BIOL 351 Week 5 Lab Manual. Texas A&M University. College Station, TX. Biology 351. 2023. Week 5 PowerPoint. Texas A&M University. College Station, TX.
- Janes D, Moyes R, Longcrier C, Basile L. 2023. Microbiology of Water. BIOL 351 Week 6 Lab Manual. Texas A&M University. College Station, TX. Biology 351. 2023. Week 6 PowerPoint. Texas A&M University. College Station, TX.
