1.   Place the Petrifilm Coliform Count plate on a flat surface.  See fig 1.

2.   Lift the top film, hold the pipette perpendicular to the plate and carefully dispense 1mL of sample or sterile hydrating solution onto the centre of the bottom film.  See fig 2.  Sterile hydrating solution is used when you intend to test a surface by direct contact.

3.   Roll the top film down onto the liquid, avoiding the entrapment of air bubbles under the top film.  See fig 3.

4.   Orient the plastic all-purpose spreader with the smooth side down (ridge side up) and place it on the top film over the liquid sample.  Press gently on the centre of the spreader to distribute the sample evenly.  See fig 4.  Avoid sliding or twisting the spreader on the film.  Remove the spreader and leave the plate undisturbed for one minute to allow the gel to solidify.

Plates treated with sterile hydrating solution should be allowed to gel for at least one hour, but may be stored in a refrigerator for up to 1 week before being used to test a surface.

5.   Incubate inoculated plates in a horizontal position (clear side up) at 35^oC for 24 hours.  Plates may be stacked up to 20 high and placed in a press-seal bag.  See fig 5.

1. Coliform Count plates will indicate all coliforms in the sample.  By definition, coliforms are the members of the family Enterobacteriaceae which ferment lactose to produce gas.  Count all colonies which appear red and which are associated with gas bubbles as confirmed coliforms.

2.   Express the count in terms of the number of coliforms per sample.

3.  The presence of many small colonies, many gas bubbles, or an overall deepening of the colour of the gel probably indicates that the sample is too concentrated to give a reliable result.  In this case, further dilution of the sample is required to obtain an accurate count.

Store unopened packs of Petrifilm Coliform Count plates in a freezer.  Allow the pack to come to room temperature before opening.  After opening and removing the plates you need, the pack may be resealed with tape and/or placed in a press-seal bag and returned immediately to the freezer.

After removal from the pack, plates should be kept in cool dry conditions (below 25^oC and 50%RH) and used within one month.

Following inoculation, plates presented to the class for examination and counting should be taped shut or placed in a press-seal bag to keep them isolated.  Follow good laboratory practice and have students thoroughly wash their hands after handling microbiological samples and equipment.  Adequate antibacterial hand wash and hand rub sanitiser solutions should be provided.

Plates with viable colonies must be disposed of in a responsible way such as by autoclaving or soaking in an appropriate disinfectant.  Alternatively, you can use a contract collection service.