4.3.2: indirect methods & rapid methods

what are the different types of indirect methods?

turbidity measurement

dry and wet weight

nitrogen content

metabolic activities

what is turbidity measurement?

microbial growth in broth results in turbidity, higher cell density, the more turbid the broth

what is used to measure turbidity?

spectrophotometer

what are the advantages of turbidity in terms of the process?

easy, quick method and useful to follow growth of culture

what is the advantage of turbidity measurement in terms of relating to other methods?

turbidity can be correlated to plate counts under identical growth conditions, extrapolate to cell density

what are the disadvantages of turbidity in terms of types of cells?

both dead and living cells contribute to turbidity

what are the disadvantages of turbidity measurement in terms of sensitivity

not too sensitive, requires at least around 10 power 6 cells/ml to be detectable

what is dry and wet weight?

separate cells from growth medium by filtration or centrifugation

how to perform wet weight?

wash with buffer or water and weight for wet weight

how to preform dry weight?

dry cells in oven

what are the advantages of dry and wet weight in terms of a specific microorganism?

good for filamentous microorganisms

why is dry and wet weight method good for filamentous microorganisms?

do not plate well, colonies may not be formed from single cells and float on surface or settle in broth

what are the disadvantages of dry and wet weight in terms of sensitivity?

fairly insensitive, requires more than 10 power 6 cells

what are the disadvantages of dry and wet weight in terms of accuracy?

difficult to accurately weight small amounts

what is nitrogen content method?

measures amount of organic nitrogen in cell mass

how to know if there is higher nitrogen content?

more cells make more proteins, therefore higher organic nitrogen content

what is metabolic activities method?

microbial growth is characterized by increased metabolic activity

how does the metabolic activities count bacteria?

measures consumption of substances, accumulation of metabolic waste products

what is the advantage of rapid methods?

fast and sensitive

what are the disadvantages of rapid methods?

expensive and results may be difficult to correlate to actual cell numbers

what are the different rapid methods?

measurement of electrical variations in culture medium

measurement of ATP

DNA techniques