Part II

Six strains of E. coli and two strains of Strept. faecalis were seeded into 12 different foods having a pH range of 2.8 to 6.7. Viability tests were run at different time intervals to study the viability of these organisms in the different foods under normal conditions. The results showed that the growth curve of E. coli in the foods depended upon the food and that the height of the curve was determined by the initial inoculation. E. coli var. communis was more viable in the foods than were the other strains. Strept. faecalis remained viable longer in some of the acid foods such as orange juice with a pH of 3.5 and mayonnaise with a pH of 3.7 than did any of the strains of E. coli. There appeared to be little difference between the viability of the two organisms in the less acid foods within the time limits studied.

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Author notes

*The Part I section was published in this Journal, July ‘54 issue, page 204.

*Since this work was completed, Litsky et al.1 found that ethyl violet was selective for gram-negative bacteria. Later they (Litsky et al.2) used glucose azide broth as a presumptive medium and ethyl violet azide broth as a confirmatory medium for the detection of enterococci in water, thereby doing away with the necessity of using the microscope and also placing the test on the same basis as the coliform test.