An abstract in the April 2006 Journal of Food Protection discussed the death rates of Salmonella, E. coli O157:H7, and Listeria in three commercially manufactured full-fat ranch salad dressings, three reduced-fat ranch salad dressings, two full-fat blue cheese salad dressings, and two reduced-fat blue cheese salad dressings. The study attempted to affirm the expectation that these dressings do not support the growth of these pathogens.
Dressings were inoculated with low and high populations of separate five-strain mixtures of each pathogen, and stored at 25 degrees Celcius for up to 15 days.
Regardless of the initial inoculation population, all test pathogens rapidly died in all salad dressings, ranging from 1 to 8 days maximum. The type of dressing and level of fat in the dressings did not have a marked effect on the rate of inactivation of pathogens.
Based on these observations, shelf-stable, dairy-based, pourable ranch and blue cheese salad dressings manufactured by three companies and stored at 25 degrees C do not support the growth of Salmonella, E. coli O157:H7, and Listeria, and should not be considered as potentially hazardous foods as defined by the U.S. Food and Drug Administration Food Code.