Pefrom serila dilutions of sample. measuring number of viable cells- non dead once. Count number of CFU on the plate. Plate Count done by eithr pour plate method(added melted agar and mixed) or spread.
Most Comon Method
Filtration - Direct Me.
Big amount of water is filltered through a vocume pump that have a filter. Holes iin the filter are smaller than most bacteria. Than, filter is put on a petri dish - colonies will grow on the filter.
Multiple tube most probable number test (MPN) -Direct Me.
Count positive tubes and compare to statistical MPN table.
Direct microscopic count
uses special microscopice slide - called Petroff-Hauser chamber. Spacial grid tells the value of sample.
Not good for counting motile bacteria
Dead bacteria will be counted as well as alive
how cloudy. Spectrophotometer used to identify hwo mach light goes through.
Transmited Light is inversaly proportinal to # of bacteria.
Absorbance - how much light is absorbed by bacteria
Estimates cells by how much by product is produced. (ex. acid or CO2)
Used for filamentous bacteria and molds. Organism is filtered, then dehydrated and weighed