Microbiological Examination of Non-Sterile Products: Methods & Standards
Aerospace corrosion testing per MIL-STD-810 evaluating alloy and coating protection performanceWhat Is Microbiological Examination of Nonsterile Products?
Microbiological examination of nonsterile products is the testing of pharmaceutical preparations, healthcare products, and similar materials that are not required to be sterile—but must still meet defined microbiological quality standards—to ensure they are safe for their intended use. This includes oral dosage forms (tablets, capsules, liquids), topical preparations, transdermal patches, inhalation products, herbal remedies, and dietary supplements.
The primary tests performed include the Total Aerobic Microbial Count (TAMC), Total Combined Yeast and Mold Count (TYMC), and tests for the presence of specified indicator organisms. Testing follows USP <61>, <62>, and <1111> (United States Pharmacopeia) and Ph. Eur. 5.1.4 / 2.6.12, 2.6.13 (European Pharmacopeia) across the pharmaceutical, nutraceutical, and personal care industries.
Regulatory Framework
| Standard | Scope |
| USP <61> | Microbiological examination—tests for TAMC and TYMC |
| USP <62> | Tests for specified microorganisms (pathogens) |
| USP <1111> | Microbiological examination—acceptance criteria |
| Ph. Eur. 2.6.12 | Microbial examination of nonsterile products (TAMC/TYMC) |
| Ph. Eur. 2.6.13 | Test for specified microorganisms |
| ISO 17516 | Microbiological limits for cosmetics |
| 21 CFR 211.113 | FDA current GMP requirements for microbiological testing |
Total Aerobic Microbial Count (TAMC)
The TAMC measures the total number of viable aerobic bacteria per gram or milliliter of product. Test methods include:
Membrane Filtration
The sample (dissolved or suspended) is filtered through a 0.45 µm membrane filter that retains microorganisms. The membrane is placed on selective agar medium and incubated. Colonies are counted after incubation. Preferred for products with low microbial counts or antimicrobial activity that must be washed away before counting.
Pour Plate and Surface Spread Plate Methods
The sample is diluted and either mixed into molten agar (pour plate) or spread onto the agar surface. After incubation, colonies are counted. Simpler than membrane filtration; less sensitive for low-count samples.
Most Probable Number (MPN) Method
A liquid dilution method for samples where plating methods are impractical. Turbidity in serial dilutions indicates microbial growth; statistical tables convert the pattern of growth to an estimated cell count.
Total Combined Yeast and Mold Count (TYMC)
Similar methods to TAMC but using selective media for yeast and mold growth (Sabouraud Dextrose Agar, DRBC agar). Incubation at 20–25°C for 5–7 days allows fungal growth.
Tests for Specified Microorganisms (USP <62>)
Certain indicator organisms must be absent from defined sample quantities, depending on the product category:
| Organism | Product Category Requiring Absence |
| Escherichia coli | Oral products, aqueous preparations |
| Salmonella spp. | Products for oral use |
| Pseudomonas aeruginosa | Non-aqueous preparations for topical use |
| Staphylococcus aureus | Non-aqueous preparations for topical use |
| Candida albicans | Vaginal preparations |
| Bile-tolerant gram-negative bacteria | Oral products |
Acceptance Criteria (USP <1111>)
Acceptance criteria depend on the route of administration and intended patient population. For example:
- Oral products (aqueous): TAMC ≤ 10³ CFU/mL, TYMC ≤ 10² CFU/mL, absent: E. coli per 1 mL
- Topical non-aqueous: TAMC ≤ 10², TYMC ≤ 10², absent: S. aureus and P. aeruginosa per 1 g
Why Choose Infinita Lab for Microbiological Testing of Nonsterile Products?
Infinita Lab provides comprehensive microbiological testing services for nonsterile pharmaceutical and consumer health products per USP <61>, <62>, <1111>, and Ph. Eur. standards. Our cGMP-compliant, ISO/IEC 17025-accredited microbiology laboratories deliver reliable, regulatory-ready results with complete documentation.
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Frequently Asked Questions (FAQs)
What is the difference between TAMC and TYMC in microbiological testing? TAMC (Total Aerobic Microbial Count) counts viable aerobic bacteria, including both gram-positive and gram-negative organisms, on non-selective agar incubated at 30–35°C for 3–5 days. TYMC (Total Combined Yeast and Mold Count) counts yeast and filamentous fungi on selective agar incubated at 20–25°C for 5–7 days. Together, TAMC and TYMC provide a complete picture of total bioburden for both bacterial and fungal contamination.
Why must method suitability (bacteriostasis/fungistasis) be performed before product release testing? Many pharmaceutical products contain antimicrobial preservatives, surfactants, or pH conditions that inhibit microbial growth in the test system. If not detected and corrected, product-induced inhibition causes false-negative results—contaminated products pass testing. Method suitability verifies that the test system can recover the test organisms in the presence of the product matrix before release testing is conducted.
What sampling plan is typically used for microbiological testing of solid oral dosage forms? Composite sampling from multiple dosage units is common for TAMC/TYMC of solid oral dosage forms—typically 10 tablets or capsules are combined and assayed together to represent the production lot. The number of composite samples and the sample size per assay are defined by USP <1111> and the applicable product specification.
What is the incubation temperature and time for TAMC per USP <61>? USP <61> specifies incubation of TAMC plates on non-selective agar (Soybean-Casein Digest Agar, SCDA) at 30–35°C for not less than 3 days (pour plate, spread plate, or membrane filtration). TYMC plates (Sabouraud Dextrose Agar with antibiotics) are incubated at 20–25°C for not less than 5 days.
Can rapid microbiological methods (RMM) be substituted for pharmacopoeial compendial methods? Yes, with validation. FDA Guidance for Industry (2004) and Ph. Eur. 5.1.6 allow alternative rapid microbiological methods (bioluminescence, impedance, flow cytometry, real-time PCR) as substitutes for compendial methods, provided they are validated to demonstrate equivalence or superiority in detection, quantification, and specificity. Validation must include a direct comparison to the reference compendial method.
