Common Microbial Culture Media and Their Performance Validation Using Standard Strains

News 8 10 月, 2024

In microbiology labs, it is essential to validate the performance of new or newly sourced culture media using standard strains before they can be used for testing. This ensures the culture media meet the required standards for microbial growth and testing. Here’s a detailed guide on commonly used microbial culture media, the standard strains used for performance validation, and their specific characteristics and applications.

1. Nutrient Broth

• Standard Strains: Staphylococcus aureus ATCC 25923, Escherichia coli ATCC 25922
• Performance: Good growth within 24 hours.
• Application: Used for enrichment of non-fastidious bacteria in clinical samples.

2. Brain Heart Infusion (BHI) Broth

• Standard Strains: Streptococcus pneumoniae ATCC 49619, Haemophilus influenzae ATCC 49247
• Performance: Good growth within 24 hours.
• Application: Enrichment of fastidious bacteria requiring rich nutrients.

3. Blood Agar

• Standard Strains:
  • Streptococcus pneumoniae ATCC 49619: Good growth, α-hemolysis, large flat colonies.
  • Streptococcus pyogenes ATCC 19615: Good growth, β-hemolysis, colonies ≥0.5 mm.
• Application: Isolation, hemolysis identification, and preservation of pathogenic bacteria.

4. Anaerobic Blood Agar

• Standard Strains: Bacteroides fragilis ATCC 25285, Clostridium perfringens ATCC 13124
• Performance: Growth within 48 hours with distinct colony characteristics.
• Application: Isolation of anaerobic bacteria.

5. Chocolate Agar

• Standard Strains: Haemophilus influenzae ATCC 49247
• Performance: Good growth, colony size ≥1 mm in 24 hours.
• Application: Cultivation of Haemophilus and Neisseria species.

6. Neisseria Selective Agar

• Standard Strains: Neisseria gonorrhoeae ATCC 49226
• Performance: Good growth, colony size ≥0.5 mm in 24 hours.
• Application: Selective isolation of Neisseria gonorrhoeae.

7. MacConkey Agar (or EMB Agar)

• Standard Strains:
  • Escherichia coli ATCC 25922: Pink (or blue) colonies in 24 hours.
  • Enterococcus faecalis ATCC 29212: No growth.
• Application: Differentiation of Gram-negative bacteria and identification of non-fermenters.

8. SS Agar

• Standard Strains:
  • Salmonella typhimurium ATCC 14028: Colorless colonies with black centers.
  • Shigella sonnei CMCC(B) 51592: Small, colorless colonies.
  • Escherichia coli ATCC 25922: Red colonies, growth inhibited.
• Application: Isolation of Salmonella and Shigella from fecal samples.

9. XLD Agar (Xylose Lysine Deoxycholate Agar)

• Standard Strains:
  • Salmonella typhimurium ATCC 14028: Red colonies with black centers, red medium.
  • Escherichia coli ATCC 25922: Yellow colonies with precipitate.
• Application: Isolation of Salmonella and Shigella.

10. TCBS Agar

• Standard Strains: Vibrio parahaemolyticus ATCC 17802
• Performance: Good growth, large green colonies.
• Application: Selective isolation of Vibrio species.

11. CCFA Agar

• Standard Strains: Clostridioides difficile ATCC 43593
• Performance: Colony growth within 48-72 hours under anaerobic conditions.
• Application: Isolation of Clostridioides difficile.

12. Biphasic Media

• Standard Strains: Staphylococcus aureus ATCC 25923, Escherichia coli ATCC 25922
• Performance: Visible turbidity and bacterial colonies.
• Application: Enrichment of sterile body fluids.

13. Löwenstein-Jensen Medium (or Mycobacteria Liquid Medium)

• Standard Strains: Mycobacterium kansasii ATCC 12478
• Performance: Rough, yellow colonies with good growth within the expected time.
• Application: Isolation of Mycobacterium species.

14. Sabouraud Agar

• Standard Strains: Candida albicans ATCC 90028
• Performance: Good growth, white colonies.
• Application: General fungal isolation and culture.

15. Chromogenic Candida Agar

• Standard Strains:
  • Candida albicans ATCC 90028: Green colonies.
  • Candida tropicalis ATCC 750: Blue colonies.
• Application: Differentiation and identification of common Candida species.

Importance of Performance Validation

Performance validation involves inoculating specific bacterial or fungal strains onto corresponding media and observing growth characteristics to confirm if the medium meets the required performance standards. If standard strains are not available, quality control strains or clinical isolates with matching characteristics can be used.

For accurate microbial testing, the media must pass performance validation. Unvalidated or failed validation media should not be used for clinical or laboratory testing purposes.