1. Colilert Presence – Absence (P – A) Test

1. Open the 100 mL plastic Colilert bottle. The bottle includes a small amount of powdered reagent that is necessary for the proper reactions, do not discard this powder.
2. Add 100 mL water sample into Colilert bottle.
3. Open the pillow tube containing the nutrient substrate and pour the contents into the water sample inside the Colilert bottle.
4. Cap and seal the Colilert bottle. Shake the bottle vigorously, repeatedly inverting the bottle until the substrate is completely dissolved.
5. Incubate the reagent/water sample mixture inside the bottle at 35 ± 0.5 °C for 24 h.
6. Observe the yellow color change in the reagent/water sample mixture. The yellow color indicates coliform is present. Clear water or no change in color indicates that coliforms are absent.
7. Expose the reagent/water sample to ultraviolet light and observe the blue fluorescence. Blue fluorescence indicates that E. coli is present. No fluorescence indicates that E. coli is absent (Figure 3).

Figure 3. P-A test negative (left), coliform positive (middle), and E. coli positive (right).

2. Colilert MPN: Quanti-tray 2000

1. Open the Colilert bottle, and 100 mL water sample into Colilert bottle.
2. Open the pillow tube containing nutrient substrate and pour contents into the water sample inside the Colilert bottle.
3. Cap and seal the Colilert bottle. Shake the bottle vigorously, repeatedly inverting the bottle until the substrate is completely dissolved.
4. Carefully open Quanti-tray 2000 by squeezing the edges at the top of the tray and pulling back the paper tab. Keep squeezing so that the tray is open.
5. Pour the reagent/water sample mixture into the tray, and then incubate the sample inside the tray at 35 ± 0.5 °C for 24 h.
6. Observe the yellow color change in the reagent/water sample mixture. Count the number of large and small wells that signal positive presence for coliforms. The yellow color indicates coliform is present. Clear water or no change in color indicates that coliforms are absent.
7. Expose reagent/water sample to ultraviolet light and observe blue fluorescence. Count the number of large and small wells that signal positive presence for E. coli. The blue fluorescence indicates that E. coli is present. No fluorescence indicates that E. coli is absent.
8. Use the Quanti-tray 2000 MPN sheet (Figure 4) to quantify the concentration for each indicator organism present in 100 mL of water. Use the spreadsheet to compare large: small positive well ratio to enumerate presence for both indicator organisms.

Figure 4. Quanti-tray negative (left), coliform positive (middle), and E. coli positive (right).