Question

Direct counts of cells in liquid samples can be performed using a Petroff-Hausser counting chamber. Research this method and describe how it compares to the viable plate count method of determining the number of CFU in a sample.

Answer 1

Petroff-Hausser counting chamber is commonly used to count bacterial cells, platelets...etc. This is widely used to count cells from liquid samples on real time basis. The other method used for bacterial count is viable cell plate count. Both these method give bacterial number in original culture, but with few distinctions.

1. The Petroff-Hausser counting is real time, whereas the viable plate count requires at least 16-20 h of incubation for colonies to be visible.

2. Petroff-Hausser method uses the dilution factor which will convert the volume of the chamber and area of the squares to bacterial per ml in original sample. In viable plate counting, we use colonies formed on the plate and serial dilution tube to get bacterial cell count per ml in original culture.

3. In Petroff-Hausser method, we first all 10ul of liquid culture onto counting chamber, cover it with coverslip and count the cells in the large and smaller squares. In viable plate count, we serially dilute ten original culture and plate appropriate volume onto nutrient agar plates.

4. One of the most important creature of Petroff-Hausser method is that we can count even those bacteria which cannot be cultured efficiently in lab, or which have long generation time. Such bacteria cannot grow quickly on nutrient plates and make the viable plate method not suitable.