Food borne diseases cause 76 million illness, 325,000 hospitalizations and 5,000 deaths in the United States each year. The CDC has also reported that 73,480 of these cases are caused by Escherichia coli O157:H7 (E. coli O157). This serotype of E. coli has been known to cause life threatening hemorrhagic colitis which sometimes leads to hemolytic uremic syndrome in humans. Mammalian reservoirs for this enteric pathogen include cattle and sheep feces. Recently published methods of isolation and detection offer an accurate and sensitive way to measure the prevalence of E. coli O157 in environmental samples such as feces. The goal of this project is to better understand the detection limit of these methods so that sensitivity of the test can be established. Using Fluorescent Activated Cell Sorting (FACS) procedures we were able to quantify the sensitivity of current methods of isolation and detection. This study demonstrates that the probability of detection of E. coli O157 was 66.6% when 1 cell was present and this probability rose to 90% when 5 cells are present.