Method for direct microbiological counting
Using a hemocytometer to directly count microorganisms under a microscope is a commonly used method for microbial counting. The advantage of this method is its intuitiveness and speed. Place the appropriately diluted bacterial suspension (or spore suspension) in the counting chamber between the hemocytometer slide and cover slide, and count under a microscope. Due to the constant volume of the counting room (0.1mm2), the total number of microorganisms per unit volume can be converted based on the number of microorganisms observed under the microscope. Due to the fact that this method calculates the sum of live and dead bacterial cells, it is also known as the total bacterial count method.
A blood cell counting plate is usually a specially designed glass slide with four grooves forming three platforms. The middle platform is divided in half by a short horizontal groove, and each side of the platform is engraved with a grid. Each grid is divided into nine large squares, and the large square in the middle is the counting room, where microbial counting is carried out.
There are generally two specifications for the scale of the counting room. One is that a large square is divided into 16 middle squares, and each middle square is further divided into 25 small squares (Figure VIII -2); Another method is to divide a large square into 25 middle squares, and each middle square is further divided into 16 small squares (Figure VIII -1, C). But regardless of the size of the counting board, the number of small squares in each large square is the same, that is, 16 × 25=400 small squares
If the side length of each large square is 1mm, the area of each large square is 1mm2. After covering with a cover glass, the height between the slide and the cover glass is 0.1mm, so the volume of the counting room is 0.1mm3.
When counting, the total number of bacteria in five squares is usually counted, and then the average value of each square is obtained. Multiplying it by 16 or 25 gives the total number of bacteria in a large square, which is then converted to the total number of bacteria in 1ml of bacterial solution.
