Difference Between Nutrient Agar (NA) and Plate Count Agar (PCA)

News 26 11 月, 2024

Introduction

For those familiar with microbiological testing, colony count testing varies across industries, including food, air, water, and food contact surfaces. While some standards require Plate Count Agar (PCA), others call for Nutrient Agar (NA). So, what’s the difference between these two culture media?

Formulations and Key Differences

The formulas for PCA and NA differ slightly:

• Plate Count Agar (PCA):
  • Ingredients: 0.5% Tryptone, 0.25% Yeast Extract, 0.1% Glucose, 1.5% Agar, Distilled Water
  • pH: 6.8–7.2
  • Used in the 2008 GB standard for colony count testing.
• Nutrient Agar (NA):
  • Ingredients: 1% Peptone, 0.3% Beef Extract, 0.5% Sodium Chloride, 1.5–2.0% Agar, Distilled Water
  • pH: 7.2–7.4

While both are suitable for colony count testing, their formulations slightly differ. Despite this, they are largely interchangeable in routine testing.

Applications and Observations

Both PCA and NA are used for culturing mesophilic bacteria and colony count measurements. Differences in results are usually negligible over a few tests. However, international studies suggest PCA may yield slightly better results in extensive trials.

When using PCA for colony count tests, specific procedural adjustments include:

1. Replacing Nutrient Agar with Plate Count Agar.
2. Adding bacterial count test papers.
3. Modifying colony count calculation formulas.
4. Using homogenizers or equivalent equipment.

Best Practices

Both PCA and NA are effective for mesophilic bacterial cultivation. While interchangeable in most cases, it’s best to adhere to the medium specified by the testing standard to ensure accuracy.