Thermo Scientific™ Oxoid™ Bile Aesculin Agar (Dehydrated)

Thermo Scientific™ Oxoid™ Bile Aesculin Agar is a differential and selective medium specifically designed for the isolation and presumptive identification of enterococci and Group D streptococci. This medium is widely recognized as an alternative to Lancefield grouping due to its ability to differentiate Group D streptococci based on bile tolerance and aesculin hydrolysis.

Key Features

1. Selective for Enterococci and Group D Streptococci:
   • Contains bile salts, which inhibit the growth of most Gram-positive bacteria other than enterococci and Group D streptococci.
2. Differential Based on Aesculin Hydrolysis:
   • Group D streptococci and enterococci hydrolyze aesculin to produce aesculetin and dextrose.
   • Aesculetin reacts with ferric ions in the medium to form a dark brown or black precipitate, indicating a positive result.
3. Easy-to-Read Results:
   • The dark precipitate formed during aesculin hydrolysis provides a clear and visible indicator for positive organisms.
4. Validated Alternative to Lancefield Grouping:
   • The medium simplifies the presumptive identification process for Group D streptococci, as demonstrated by Swan (1954).
5. High Specificity:
   • Inhibits non-target Gram-positive bacteria while allowing growth of target organisms.

Specifications

Preparation Directions

1. Medium Preparation:
   • Suspend 41.0 g of Bile Aesculin Agar powder in 1 liter of distilled water.
   • Heat the mixture with frequent agitation to dissolve the powder completely.
   • Boil for 1 minute to ensure the medium is fully dissolved.
   • Do not autoclave; dispense the medium into sterile Petri dishes or tubes.
2. Storage:
   • Store prepared plates at 2–8°C. Avoid prolonged exposure to light.

Composition (Typical Formula per Liter)

Applications and Use Cases

1. Isolation and Presumptive Identification:
   • Differentiates Group D streptococci (e.g., Streptococcus bovis) and Enterococcus species (e.g., Enterococcus faecalis, Enterococcus faecium) based on aesculin hydrolysis and bile tolerance.
2. Clinical Diagnostics:
   • Used in diagnostic microbiology for identifying enterococcal infections in fecal, urine, and blood specimens.
   • Enterococci are significant as both commensal flora and opportunistic pathogens in human infections, including UTIs and endocarditis.
3. Food and Water Testing:
   • Applied in food and water microbiology to detect enterococci as indicators of fecal contamination.
4. Research Applications:
   • Supports studies on the resistance and pathogenicity of Enterococcus species, particularly in healthcare settings.

Result Interpretation

Advantages

1. High Specificity:
   • Effectively differentiates target organisms from other Gram-positive bacteria.
2. Clear Visual Identification:
   • Aesculin hydrolysis produces a distinct black/brown precipitate.
3. Selective Inhibition:
   • Bile salts selectively suppress non-Group D Gram-positive bacteria.
4. Easy Preparation:
   • Dehydrated medium simplifies lab workflows.
5. Validated Diagnostic Tool:
   • A widely accepted alternative to Lancefield grouping.

Storage and Shelf Life

• Dehydrated Medium: Store at 10–30°C in a dry location.
• Prepared Medium: Store at 2–8°C for up to 3 days.

References

1. Facklam R. R. and Moody M. D. (1970). Appl. Microbiol. 20, 245-250.
2. Isenberg H. D., Goldberg D., and Sampson J. (1970). Appl. Microbiol. 20, 433-436.
3. Swan A. (1954). J. Clin. Path. 7, 160-163.

The Thermo Scientific™ Oxoid™ Bile Aesculin Agar offers a reliable and efficient method for isolating and differentiating enterococci and Group D streptococci, making it a valuable tool for clinical, food, and water microbiology laboratories. Let me know if further details or comparisons are needed!