A recently described differential agar medium was used to study strain interactions in two-strain mixtures of Streptococcus lactis and Streptococcus cremoris. Two S. cremoris strains (ML4 and DR7) exhibited marked dominance over four S. lactis cultures. One S. cremoris strain, designated 1, showed excellent compatibility in all combinations. Streptococcus cremoris HP was progressively suppressed by all S. lactis strains. The associative growth patterns at 32 C and 21 C were similar irrespective of the initial cell numbers of the component strains.

The technique described in this paper could be used in conjunction with phage tracer methods to investigate growth relationships among mixed strain lactic starters containing more than one strain each of S. lactis and S. cremoris.

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Author notes

1Journal Paper No. J-6744 of the Iowa Agriculture and Home Economies Experiment Station, Ames, Iowa. Project No. 1838.

2Post-doctoral Research Associate under Training Grant FD00005-04 from the Food and Drug Administration, U. S. Public Health Service.

3Present address: Department of Biology, Southwestern Union College, Keene, Texas 76059.