Results
Through the interpretation of the data collected by our confirmation tests we were able to determine that we were indeed successful in isolating Lactobacillus casei.
Streak Plates:
The plates showed smooth, opaque, non-pigmented colonies, consistent with the colonies produced by Lactobacillus casei.
Microscopic Evaluation:
Gram positive, short rods were visible under the microscope with the gram stain, these rods were occasionally in short chains, all characteristics that support that L. casei is the isolate. In addition, no spores were visible with the gram stain.
Confirmation Tests
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Test Preformed |
Observation/ Result |
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No bubbling, therefore catalase negative. Supports L. casei as the isolate, because this organism is catalase negative |
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There was only bacteria growth along the stab line. Supports L. casei as the isolate, as it is non-motile. |
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The mannitol tube inoculated with the isolate showed a change in color to yellow/orange. Supports L. casei as the isolate, because there was a drop in pH in the fermented sugar tube. |
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Growth was present in both of the OF tubes, and yellowing was also present in both tubes. Supports L. casei, as the isolate is able to use fermentation as an energy pathway |
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Inoculation of ADT CaCO2 plates |
Clearing was present on the plate. Supports L. casei, as Lactobacillus species cause clearing on this type of plate. |
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Inoculation of Nutrient Broth |
There was growth in a slime layer on the top of the tube, these slime layers settled at the bottom of the tube. Supports L.casei, as this organism creates a slime layer when present in spoiled juices. |
When initially attempting to isolate one of the many organisms found in the orange juice as Lactobacillus casei, the presence of gram positive rods and the negative results of the catalase test were the most important characteristics. Once we isolated an organism that fit the characteristics of Lactobacillus casei we preformed our confirmation tests to prove that the isolate was L. casei. Of the confirmation tests, the presence of clearing on the ADT CaCO2 plates was important, as clearing indicates the presence of Lactobacillus species. In addition, the acid production in the mannitol tubes, and the yellowing of the OF tube with oil, indicating the ability to ferment were also critical tests to confirm the presence of L. casei. The nutrient broth test, and the motility stab were further supports, but not absolutely critical to determine that the isolate was L. casei.