Gram bacteria.pdf
Figure 1. Bacterial Growth Curve Figure 2. Determination of Generation Time In this lab you will estimate numbers of bacteria by the two most widely used methods: viable plate count and spectrophotometric analysis. In liquid culture, the medium appears more and more cloudy as the bacteria increase in number by division. A tube of bacteria will tend to reflect light so that less light is transmitted through the tube. A spectrophotometer can measure the amount of light passing through the tube, or conversely the amount of light absorbed. These measurements of turbidity or optical density (OD) are not direct measurements of bacterial numbers, but an indirect measurement of cell biomass that includes both living and dead cells. As the bacterial cell population increases, the amount of transmitted light decreases, increasing the absorbance reading on the spectrophotometer. (Fig. 3,4). If one takes readings of the same culture over time, the absorbance readings will increase as the cell n...
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