Direct microbiological microscopic counting
Direct counting under the microscope using a haematocrit plate is a commonly used method of microbial enumeration. The advantage of this method is that it is intuitive and rapid. The appropriately diluted bacterial suspension (or spore suspension) is placed in the counting chamber between the slide and coverslip of the haematocrit plate and counted under the microscope. Since the volume of the counting chamber is constant (0.1 mm2), the number of microorganisms observed under the microscope can be converted to the total number of microorganisms per unit volume. This method is also known as total bacterial counting because it counts the sum of live and dead organisms.
A haematocrit plate, usually a special slide with three platforms consisting of four slots. The middle platform is divided into two halves by a short horizontal groove, each side of the platform is engraved with a square grid, each square grid is divided into a total of nine large squares, the middle of the large square that is the counting chamber, the microbial counting is carried out in the counting chamber. The blood counting plate is shown in Figure VIII-1.
The scale of the counting chamber is generally of two sizes, one in which a large square is divided into 16 medium squares, each of which is divided into 25 small squares (Figure VIII-2), and the other in which a large square is divided into 25 medium squares, each of which is divided into 16 small squares (Figure VIII-1, C). However, the number of small squares in each large square is the same for either size of counting board, i.e., 16 × 25 = 400 small squares, as in Figure VIII-2.
The side length of each large square is 1 mm, so the area of each large square is 1 mm2, and after covering the coverslip, the height between the slide and coverslip is 0.1 mm, so the volume of the counting chamber is 0.1 mm3.
When counting, usually count the total number of bacteria in five middle squares, and then get the average value of each middle square, then multiply it by 16 or 25 to get the total number of bacteria in one big square, and then convert it to the total number of bacteria in 1ml of bacterial solution.
