Robust explanations of a coliform test: what a positive result from local river

Question

Robust explanations of a coliform test: what a positive result from local river water samples mean. (Not all coliforms are pathogens right?) and what they imply about the environment at large?

Robust explanations of a enrichment assay: what would a postive and negative result look like? (for dextrose, sitrose, glucose, and formate), and what they imply about the environment at large?

Robust explanation of a resazurin assay: what does a postive and a negative result of a river water mean? and what does it imply about the enviroment at large?

Explanation / Answer

Coliform test : the coliform test - Most probable number test, is completed in three steps with the presumptive test as the first step followed confirmed test and completed test. In a confirmed test , the presence of coliforms is confirmed by inoculating in EMB agar . The EMB agar would inhibit Gram positive organisms and only Gram negative coli forms grow. The coliform she that grow on the agar where growth of E.coli and E.aerogenes can be grown and distinguished.   

Negative test is considered when only E.aerogenes is observed on the plate. The test is only considered positive if both E.coli and E.aerogenes appear on the plate. The test is considered positive in the presence of E.coli since E.coli is an indicator of fecal contamination, as E.coli is generally not found in water or soil, and E.aerogenes is found out of intestinal tract. Thus, all coli forms are not pathogenic.

Resazurin cell viability assay : Resazurin would detect the cell viability by converting the non fluorescent due resorufin by chemically reducing growth medium from the cell growth. With a continuous cell growth, there is a maintained reduced environment. Because of growth, there is a reduction caused which results in change in the non flour event blue dye to a fluorescent red form. The fluorescence generated is proportional to the number of living cells present in that particular sample. The fluorescence is measured at 530-560 nm and excitation is measured at 590nm.

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