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Standard Plate Counts

The Standard Plate Counts test evaluates both total aerobic bacterial and total mold and yeasts. Plate counts can be performed by membrane filtration, pour plates, or spread plate methods. This test is appropriate for all nonsterile products and provides a standardized means of determining the density of heterotrophic bacteria or microbial content of the sample.

Standard Plate Count testing is suitable for pharmaceutical raw materials, nonsterile products such as liquids and powders, transdermal patches, and dietary supplements.

This test is recommended by USP General Chapter 61, USP General Chapter 1227, and the Bacteriological Analytical Manual (BAM). The advantage of using Nelson Labs is our unique validated process for the performance of harmonized testing, as recommended in USP General Chapter 61, including the appropriate media quality control and monitors. Our highly qualified team is also proficient at the plate count validation process, which ensures neutralization and recovery of the microorganisms. The plate count method used by Nelson Labs can be adapted for compliance for both USP and BAM standards.

Applicable Standards

  • USP 1227
  • USP 61

Testing Locations

Study Outline

The raw plate count results for standard agar plates should be within 25 to 250 colony forming units (CFU) or reported as an estimate. The recommended counting range for Aspergillus niger and other filamentous colonies is between 8 and 80 CFU per plate. If no colonies are found on the plates, the result should be reported as less than the sample dilution.

All test monitors display environmental and test control as defined by the alert and action levels described in the procedure. Any colonies that are found on the negative test monitor plates are compared to the test plates to see if there is contamination found in the test system. All observations are noted with the data (e.g., representative colonies). The positive test monitors, where applicable, display growth.

Procedure: An aliquot of the sample or appropriate dilution(s) is plated in triplicate on soybean casein digest agar for fungi. The samples are spread evenly with a sterile, bent, glass rod. The plates are allowed to dry at room temperature then inverted and incubated.

If you have additional questions about Standard Plate Count test services, or would like to consult with the experts at Nelson Labs, just send us a request or call us at +1 (801) 290-7500.