E. Coli ColiQuant Kits:

White Pads, Colored Inserts, Forceps, Variability...

Adah from Texas tested both of our new ColiQuant kits with her middle school students.

A. The kit only has 5 white pads. According to the kit developer, the white pad should not be contaminated because the organisms get trapped by the black grid pad on top of it. The pads can be used multiple times with or without sterilization in a microwave, as suggested in the procedure manual. It would be an interesting experiment if one group tested a highly contaminated source and then immediately tested some sterile water with the same filter. The students could determine if there was any carryover and why.

Q. Not enough colored inserts showing all the different colors of organisms growing from a contaminated water source...

A. This prompted us to increase the number of colored inserts from one to five per kit so that 5 teams can read their bacterial growth simultaneously.

Q. No plastic forceps (ColiQuant MF) to be used to place the sterile grid filter paper in the filter chamber...

A. I agree it would be nice if the forceps were sterile, but we couldn’t add forceps to the cost of the kit. I recommend swabbing metal forceps with an alcohol swab or cotton ball soaked in hydrogen peroxide or alcohol. After drying, the forceps can be used to touch the filters. The chance of having E. coli on the forceps after physically wiping the tips is low.

Q. Variable results between MF (3-30035) and EZ (3-0034) kits...

A. the main reason why results vary between the kits is the large difference in sample size. The larger the sample, 100ml (MF) vs 1 to 5 ml (EZ), the higher the probability that E. coli or coliforms will grow, especially if they are few and far between. To compare results, you have to use the same sample, stored under the same conditions, and run the test at the same time and same incubation temperatures and times. Also note in the procedures how many colonies are statistically significant on the different plates.

Q. MF kit not practical because of the sterilization procedures...

A. the kit manufacturer recommends microwaving OR thoroughly rinsing with clean water or alcohol the inside of the filtration chamber which holds the unknown sample AND completely drying inside with a clean paper towel. He believes that the plastic is so smooth and slippery that physical removal of any remaining water droplets from the previous sample is enough to prevent carryover. I already talked about the white pads in #1.

Q. Plates too small (MF kit 3-0035)...

A. these are standard RODAC plates used in several industrial applications. The procedure is an EPA approved method for finished wastewater testing. In order to change the procedure, it would have to be resubmitted to the EPA.