A variety of techniques are available to monitor bacterial growth, either by determining the number of cells in the population or their total mass, or by detecting their products. The choice depends on various characteristics of the sample and the goals of the measurements. Characteristics of the common methods for measuring bacterial growth are summarized in table 4.7.
Direct cell counts are particularly useful for determining the numbers of those bacteria that cannot be grown in culture. Unfortunately, they generally do not distinguish between living and dead cells. The simplest of these, the direct microscopic count, requires a relatively high concentration of bacteria in the sample being examined. More powerful methods use sophisticated equipment that count cells and other particles suspended in liquid.
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