Final answer:
A positive TC sample should be checked for the morphology, distribution, and coloration of microbial growth, and the results should be confirmed to rule out any errors in the procedure.
Step-by-step explanation:
When a student has obtained a positive TC (total coliform) sample in a microbiological test, it indicates the potential presence of pathogens and fecal contamination. To verify the results, the student should check for several key factors:
- Distribution and morphology of microbial growth, which in a positive reaction will appear as moderate-to-large sized dark clumps with a uniform distribution over the surface of the test circle.
- The coloration of the background which should be a blue-green, indicating the metabolic activity of the coliform bacteria.
- Ensuring that the observed results match the expected appearance of a positive TC sample. If results differ, there may have been an error in procedure, and a retest might be necessary.
- Check if the results seem reasonable. In cases of an unexpectedly large or high-concentration result, a confirmation step or dilution might be required to ensure accuracy.
To conclude, a positive TC sample needs careful inspection of morphology, coloration, and distribution of colonies, any unexpected anomalies, and a reasonableness check to rule out procedural errors that can influence test results.