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Measuring Microbial Growth

Measuring Microbial Growth. Lab 6. Measuring Cell Growth. Number of Cells per milliliter of liquid cells/ml Bacterial cultures contain millions of cells Direct Vs. indirect counts Direct Counts mean actually counting cells More accurate, but takes a lot longer

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Measuring Microbial Growth

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  1. Measuring Microbial Growth Lab 6

  2. Measuring Cell Growth • Number of Cells per milliliter of liquid • cells/ml • Bacterial cultures contain millions of cells • Direct Vs. indirect counts • Direct Counts mean actually counting cells • More accurate, but takes a lot longer • Indirect Counts mean estimating the number of cells based on turbidity in liquid or dry weight. • Less accurate, but quick • Total Count vs. Viable count • Total countall cells in a culture • Viable countonly live cells

  3. Turbidity Method • Spectrophotometer • Measure % transmittance • Amount of light going through culture • Transmittance is inversely proportional to turbidity (cell concentration) • As turbidity increases cell number increases and transmittance decreases • Indirect and Total Count

  4. Turbidity and Transmittance

  5. Plate Counts • Direct Viable counts • The idea is to evenly spread the culture across a plate and count the colonies • Each colony represents a cell in the original culture. • Problem: If we have a culture that has 1x106 cells/ml and we put 1 ml on the plate will we have isolated colonies?

  6. Plate Count • We must dilute first • If we put 1ml of culture into 9 ml of sterile media we have performed a 1/10 serial dilution (SD) • Formula: SD=AT/TV • AT=amount of culture transferred • TV=Total volume after transfer (1ml + 9 ml) • What if we did 5 serial dilutions on that culture that had 1 x 106 cells/ml

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