Culture media for enterococci and group D-streptococci

Area of Science:

• Food Microbiology
• Microbial Diagnostics
• Public Health

Background:

• Lancefield group D-streptococci, including the genus Enterococcus, are common contaminants in food, particularly from animal sources.
• Traditional serological grouping may be insufficient for classifying streptococci within the food chain.
• Accurate identification of enterococci is vital for food hygiene monitoring systems.

Purpose of the Study:

• To review and evaluate the selectivity and productivity of various selective media for isolating streptococci and enterococci from food.
• To provide guidance on selecting appropriate media for food hygiene monitoring.

Main Methods:

• Literature review of over 100 described selective media modifications.
• Comparative analysis of the selectivity and productivity of commonly used media: citrate azide tween carbonate agar (CATC), kanamycin aesculin azide agar (KAA), M-enterococcus agar (ME), aesculin bile azide agar (ABA), and thallous acetate tetrazolium glucose agar (TITG).
• Assessment of media performance based on cultivation method (plate count, membrane filter) and contamination levels.

Main Results:

• No single medium demonstrated complete selectivity for all group D-streptococci or enterococci.
• Certain media exhibited high selectivity for specific Enterococcus species, such as Enterococcus faecalis, an indicator of human pollution.
• Commercial media formulations can vary significantly in recipe and performance.

Conclusions:

• Selection of selective media requires careful consideration of the specimen type, cultivation method, and contamination level.
• Confirmatory tests are essential, especially when evaluation experience is limited.
• Parallel testing of selectivity and productivity against appropriate organisms is recommended for selective enterococci media.