SF medium is a selective medium, developed in the 1940s, to test for fecal contamination of milk and water. Only certain gram-positive cocci can grow in this medium. Why is it named SF? Using this medium, which genus will you culture?
A selective media is the one which allows the growth of only certain organism with selective properties to ensure that any other organisms do not grow on the media.
Streptococcus faecalis is a gram-positive cocci which contaminates milk and water through the fecal route as it inhabits the gastrointestinal tracts of several mammals including humans.
The media in which Streptoccous faecalis grows is termed as SF indicating the first letter of the genus and second for the species and being a selective media it can only culture the genus Streptococcus.
