Complete remaining testing procedures

Dilutions for the CBT EC+TC MPN Kit

The Aquagenx Compartment Bag Test (CBT) was originally designed to test drinking water sources. However, the CBT EC+TC MPN Kit is easily adapted for more contaminated waters with higher concentrations of bacteria such as surface water and wastewater, and for waters with higher allowable limits of bacteria.

This is accomplished by diluting CBT samples. The sections below provide guidance on the sample volume and diluent volume per 100 mL test.

Any dilution beyond 1:100 that still gives all positive (blue) compartments in the Aquagenx Compartment Bag means the water is very high risk and is not suitable for drinking without treatment to eliminate the presence of E. coli, or to reduce E. coli  to very low numbers.

Diluent

​Dilution water needs to be free of E. coli, preferably sterile water, such as:

• Standard Methods phosphate buffer
• Autoclaved or boiled reagent water
• Autoclaved or boiled tap water
• High quality, certified bottled water. Some bottled waters are produced locally and are microbiologically unsafe.
• Distilled water from a commercial source and sold in properly sealed bottles. While not necessarily sterile, it should be free of E. coli.

Surface and Recreational Waters

The Aquagenx Compartment Bag can be used to test rivers, streams, creeks, marine waters and fresh recreational waters for E. coli and total coliforms using a 1:10 dilution.

1:10 Dilution

Steps for 1:10 dilution:

• Collect 10 mL sample with a pipette
• Add 10 mL sample to Thio-Bag
• Add 90 mL diluent to Thio-Bag (fill Thio-Bag to 100 mL fill line)
• Add our EC+TC growth medium to the Thio-Bag and dissolve the medium
• Pour contents of Thio-Bag into Aquagenx Compartment Bag
• Proceed with remainder of testing procedures

→1:10 Dilution instructions for surface and wastewaters are found in Product Documents 

Wastewater

E. coli and total coliforms can be detected and quantified by the CBT EC+TC MPN Kit in municipal and urban wastewater. 

For such urban wastewater, the dilution factor may need to be 1:100, 1:1,000, 1:10,000 or even more, depending on the anticipated bacteria concentration. When the sample is diluted, any toxic chemicals present in the sample are also diluted. Dilution of those chemicals does not interfere with the growth of the E. coli or total coliforms present in the CBT sample.

Any dilution beyond 1:100 that still gives all positive (blue) compartments in the Aquagenx Compartment Bag means the water is very high risk and is not suitable for drinking without treatment to eliminate the presence of E. coli, or to reduce E. coli  to very low numbers.

1:100 Dilution

If the expected results are in the range of 900-11,000 E. coli or total coliforms/100 mL, use a 1:100 dilution by doing two serial 1:10 dilutions.

Steps for 1:100 dilution:

• Collect 10 mL sample with a pipette
• Add 10 mL sample to Thio-Bag
• Add 90 mL dilutent to Thio-Bag
• Take 10 mL from the above diluted sample, add it to a second 100 mL Thio-Bag. Add 90 mL of diluent.
• Add our EC+TC growth medium to the second Thio-Bag and dissolve the medium
• Pour contents of the second Thio-Bag into the Aquagenx Compartment Bag and proceed with testing procedures

1:1000 Dilution

If the expected results are in the range of 9000-110,000 E. coli or total coliforms/100 mL, use a 1:1000 dilution by doing three serial 1:10 dilutions.

Steps for 1:1000 dilution:

• Collect 10 mL sample with a pipette
• Add 10 mL sample to Thio-Bag
• Add 90 mL dilutent to Thio-Bag
• Take 10 mL from the above diluted sample, add it to a second 100 mL Thio-Bag, and then add 90 mL of diluent
• Take a 10 mL sample from the second Thio-Bag, add it to a third 100 mL Thio-Bag, and then add 90 mL of diluent. 
• Add our EC+TC growth medium to the third Thio-Bag and dissolve the medium
• Pour contents of the third Thio-Bag into the Aquagenx Compartment Bag and proceed with testing procedures