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Improved isolation and differentiation of enterococci in cheese
Applied Microbiology
|September 1, 1974
Summary
A new enterococcus selective differential (ESD) medium offers faster growth and improved differentiation of Streptococcus faecalis and Streptococcus faecium strains in cheese. This medium aids in the rapid, presumptive identification of enterococci.
Area of Science:
- Microbiology
- Food Science
- Diagnostic Microbiology
Background:
- Enterococci are important indicators in food safety and quality control, particularly in cheese production.
- Accurate and rapid identification of enterococci is crucial for monitoring food products.
- Existing selective media have limitations in terms of speed and differentiation capabilities.
Purpose of the Study:
- To document the efficacy of an enterococcus selective differential (ESD) medium for isolating and differentiating enterococci from various cheese types.
- To compare the performance of the ESD medium with other established selective media (KF, PSE, RSH, SCR).
- To evaluate the sensitivity, specificity, and utility of the ESD medium for rapid presumptive identification of enterococci.
Main Methods:
- Isolation and cultivation of enterococci from eight different cheeses using the ESD medium.
- Comparative analysis of colony formation rate, size, and differentiation on ESD versus KF, PSE, RSH, and SCR media.
- Biochemical and serological testing of 1,077 isolates for presumptive identification.
- Evaluation of tetrazolium salt (TTC) reduction for differentiating Streptococcus faecalis from Streptococcus faecium.
Main Results:
- The ESD medium supported the fastest growth rate and largest colony size, enabling counts within 17 hours of incubation, compared to 24-48 hours for other media.
- ESD, SCR, and RSH media yielded comparable high percentages of enterococci (58-66%), while KF and PSE yielded lower percentages (21.1-30.7%).
- The ESD medium demonstrated improved differentiation of TTC-reducing Streptococcus faecalis from TTC-nonreducing or faintly reducing Streptococcus faecium.
Conclusions:
- The ESD medium is effective for the isolation and differentiation of enterococci from cheese.
- ESD offers significant advantages in terms of reduced incubation time and enhanced colony differentiation.
- The utility of ESD for rapid, presumptive identification of enterococci in food matrices is confirmed.