Methodology Problems

The first pic shows plates that have no colonies. We have no idea what happened, except that this has happened twice before, and gives us no data, after the time spent on collection, filtration, plating, and incubation. We suspect that the immersion of our plates in plastic bags, in water at 44.5C is not always working right. We acquired a dry incubator, designed specifically for coliforms, and automatically kept at 44.5C.  The last #8 site test was done in the dry incubator, and worked well (see second pic).

            In this pic, Alex shows how the plates are loaded into slots. The closet is then closed, and the temperature is accurately held at 44.5C. This dry incubator works very well.