If you wanted to determine how many people were in your class,you would look around the room and count each individual. Even thesmallest amounts of broth contain too many bacteria to countindividually. To determine how many bacteria are in a given sample,microbiologists use a number of different methodologies includingstandard plate counts following serial dilutions, directmicroscopic counts, determining the most probable number, usingfiltration followed by standard plate counts, measuring turbiditywith a spectrophotometer, measuring the metabolic products of apopulation, and determining the dry weight of the cells in theculture. (1) Which of these methods are best to use to determinethe number of viable cells? What do these methods have in common?(2) Which of these methods would you most likely use if youexpected your density of cells to be very low? (3) Explain forwhich methodologies you might have to make a serial dilution andwhy dilutions may be necessary. (4) If you plated 1 ml of a1:10,000 dilution and recovered an average of 27 colonies, how manycells per ml were there in the undiluted (stock) culture?
