Microbiology serial dilutions problem: Coliforms are Gram-negative, lactose ferm
ID: 72125 • Letter: M
Question
Microbiology serial dilutions problem:
Coliforms are Gram-negative, lactose fermenting bacilli such as Escherichia coli that are indicators of the presence of human feces in water samples. Following a tropical storm, a microbial ecologist collects 1 liter of ocean water to analyze for the number of coliform bacteria present. The beaches must be closed for swimming if the coliform count exceeds 1,000 bacteria per 100 mL of water. What minimum CFU/mL in this sample would indicate that the beaches should be closed?
Explanation / Answer
CFU- it is the Colony Forming Unit
= no. of colonies X dilution factor/volume of culture plate.
=dilution factor = number of colonies/ml plated/ cfu/ml
=1000X10^3
=1000000 cfu/ml