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Agar medium for differential enumeration of lactic streptococci
M S Reddy1, E R Vedamuthu, C J Washam
1Department of Food Technology, Iowa State University, Ames, Iowa 50010.
Applied Microbiology
|December 1, 1972
Summary
A new agar medium differentiates lactic streptococci by utilizing lactose, arginine, and calcium citrate. This method allows for clear identification of Streptococcus cremoris, Streptococcus lactis, and Streptococcus diacetilactis in cultures.
Area of Science:
- Microbiology
- Food Science
Background:
- Accurate identification of lactic streptococci is crucial for dairy fermentation processes.
- Existing methods for differentiating these bacteria can be complex or time-consuming.
Purpose of the Study:
- To develop a novel agar medium for the differential identification of key lactic streptococci species.
- To enable efficient enumeration and differentiation in both pure and mixed cultures.
Main Methods:
- A specialized agar medium was formulated with arginine, calcium citrate, potassium hydrogen phosphate, calcium carbonate, and bromocresol purple.
- The medium utilizes lactose fermentation, arginine metabolism, and calcium citrate utilization for differentiation.
- Incubation at 32°C for 36 hours and 6 days allowed for distinct colony observations.
Main Results:
- Streptococcus cremoris colonies appeared yellow after 36 hours due to lactose fermentation.
- Streptococcus lactis and Streptococcus diacetilactis colonies appeared white.
- Streptococcus diacetilactis colonies showed clear zoning after 6 days due to calcium citrate degradation, distinguishing them from the other two species.
Conclusions:
- The developed agar medium provides a reliable and efficient method for differentiating Streptococcus cremoris, Streptococcus lactis, and Streptococcus diacetilactis.
- This medium is suitable for quantitative differential enumeration, offering an advantage over existing methods.