Microbial Testing for Herbal Supplements: Why USP <61> and <62> Aren't Optional

Of all the categories we test at Qalitex, herbal dietary supplements generate the most re-tests. Not because the brands are careless — most of them are genuinely trying to do things right — but because herbal ingredients are botanically complex, grown outdoors in soil, and handled by multiple parties before they reach a manufacturing floor. By the time a lot of turmeric root powder or ashwagandha extract arrives at a facility, it has had plenty of opportunity to accumulate microbial contamination that synthetic ingredients simply don’t face.

That reality makes USP <61> and <62> testing not just a regulatory checkbox but a practical necessity. And yet, we regularly see brands — especially those newer to the space — who are unclear on what these tests actually measure, what a passing result means, and where the testing protocol should sit in their quality timeline. This post is an attempt to make that clearer.

Why Herbal Ingredients Start With a Higher Microbial Baseline

Synthetic nutrients like ascorbic acid or magnesium glycinate are produced in controlled manufacturing environments. They have predictable, low bioburden. Botanicals are a different story.

Plants grow in open fields or forests, in direct contact with soil organisms, irrigation water, birds, and insects. Post-harvest, they’re dried — sometimes in open-air facilities with inconsistent temperature control — and then milled, extracted, or powdered before shipping. Each step is an opportunity for microbial populations to establish themselves or cross-contaminate. Spore-forming bacteria like Bacillus species are especially common because their spores survive drying and mild heat treatments that would kill vegetative cells.

Moisture is the other variable. Herbal powders that absorb humidity during transit can experience significant microbial growth between the time they leave the supplier’s facility and the time they arrive at yours. A water activity (a_w) reading above 0.60 is generally considered the threshold below which most microbial growth stalls — but a lot changes in a shipping container sitting in a port during summer.

The practical result: herbal raw materials routinely carry total aerobic microbial counts (TAMC) in the range of 10² to 10⁵ CFU/g before any treatment. Some botanicals, particularly those with dense plant matrices like root powders, can test even higher. That wide variance is exactly why incoming raw material testing isn’t optional under 21 CFR Part 111 — it’s required.

Decoding USP <61> and <62>: What Each Test Actually Measures

These two chapters work in tandem, and understanding what each one does — and doesn’t — tell you is important for building a coherent protocol.

USP <61>, formally titled Microbiological Examination of Nonsterile Products: Microbial Enumeration Tests, measures the total population of microorganisms in a sample. Specifically, it produces two numbers:

• TAMC (Total Aerobic Microbial Count): the count of bacteria capable of aerobic growth, reported in CFU/g or CFU/mL
• TYMC (Total Yeast and Mold Count): the count of fungi, reported the same way

These are quantitative tests. They tell you how many organisms are present, but not which organisms. A sample could pass USP <61> with flying colors and still contain a low-level Salmonella contamination, because that pathogen might be present in numbers that don’t dramatically move the total count.

USP <62>, Tests for Specified Organisms, handles the qualitative piece. It’s a presence/absence test for specific dangerous pathogens, including:

• Salmonella species (absence required in 25 g of sample)
• Escherichia coli (absence required in 1 g of sample)
• Staphylococcus aureus (absence required in 1 g for certain product categories)
• Pseudomonas aeruginosa (relevant primarily for topical products)
• Candida albicans (required for certain topical and oral preparations)
• Bile-tolerant gram-negative bacteria (BTGN), which serve as a broader indicator of fecal contamination

The detection methodology matters here. USP <62> uses enrichment culture steps specifically designed to amplify low-level pathogen populations that might be masked in a total-count assay. A sample with 50 CFU/g of Salmonella would very likely pass USP <61> — the total count would look fine — but fail USP <62> conclusively. That’s why running one without the other creates a real compliance gap.

Acceptance Criteria Most Brands Get Wrong

FDA’s 21 CFR Part 111 doesn’t prescribe specific microbial limits directly — it requires manufacturers to establish specifications. But USP provides the reference point that the industry and FDA both use. For non-sterile oral dosage forms (which covers the vast majority of dietary supplements), the general guidance is:

• TAMC: ≤ 10,000 CFU/g (10⁴ CFU/g)
• TYMC: ≤ 1,000 CFU/g (10³ CFU/g)
• Salmonella spp.: Absent in 25 g
• E. coli: Absent in 1 g
• BTGN bacteria: ≤ 100 CFU/g

A few things brands misunderstand about these limits:

They apply to finished product — but your raw materials need their own specs. Manufacturers often interpret the 10,000 CFU/g limit as applicable only to their finished capsule or tablet. But if your incoming herbal raw material is arriving at 50,000 CFU/g, you either need a validated microbial reduction step (like steam sterilization or irradiation) built into your process, or a supplier quality program that prevents that material from entering your facility in the first place. Finished-product testing alone doesn’t solve an upstream contamination problem.

A result near the limit is a warning signal, not a routine outcome. A TAMC of 9,800 CFU/g technically passes, but it’s telling you that your process or raw material quality is operating at the edge of the acceptable range. We flag results above 5,000 CFU/g as a quality concern worth investigating regardless of whether they formally fail, because finished product results don’t account for normal assay variability and the possibility that a different sample from the same lot might test higher.

Pathogen absence is non-negotiable and non-correctable. A single confirmed positive for Salmonella in a finished supplement lot means that lot cannot be released. There’s no averaging, no re-sampling strategy that resolves a positive result under USP <62>. The lot is non-conforming under 21 CFR Part 111, full stop. That’s why catching contamination at the raw material stage — before it enters blending and is distributed across thousands of units — is so much less costly than finding it at finished-product release.

How to Build a Microbial Testing Protocol That Actually Works

The brands we see consistently passing release testing are the ones who treat microbiology as a process control tool, not just a release gate. That means testing at multiple points and using the data to make decisions, not just to generate paperwork.

Test incoming raw materials before they enter quarantine release. Every lot of herbal material should have a certificate of analysis from the supplier, but that COA should be verified, not trusted blindly. Run at minimum a TAMC/TYMC screen on incoming lots, and run the full USP <62> panel on high-risk materials — root powders, whole dried plant material, and anything sourced from regions with documented agricultural contamination concerns.

Understand your risk tiers. Not every ingredient carries equal risk. Crystalline vitamins and minerals can often be managed with reduced testing frequency once a supplier’s track record is established. Botanicals — especially roots, seeds, and minimally processed whole-plant ingredients — warrant testing on every lot, every time.

Validate any microbial reduction steps you’re relying on. If your process includes a step intended to reduce bioburden (flash pasteurization, gamma irradiation, ethylene oxide treatment), that step needs a validated kill claim supported by challenge studies. “We send it out for irradiation” is not a validated step unless you can document what organism populations were present before treatment and what the log reduction achieved was.

Use an ISO 17025 accredited supplement testing lab for finished-product release. Accreditation matters here because USP <61> and <62> methodologies require validated equipment, trained analysts, and documented method suitability confirmation. A lab working outside of an ISO 17025 quality system may produce results that aren’t defensible if FDA examines your records during an inspection. The accreditation is the evidence that the testing was conducted under appropriate controls — and FDA investigators do ask about it.

Set internal alert limits that are tighter than your release specifications. If your specification is 10,000 CFU/g, set an internal alert at 5,000 CFU/g and a rejection limit at 8,000 CFU/g. That two-step system gives you time to investigate and make a decision before you’re in a binary pass/fail situation at the release threshold.

The Bigger Picture

Microbial contamination in herbal supplements is not a hypothetical risk. FDA has issued multiple warning letters and initiated recalls tied specifically to Salmonella contamination in botanical products, and several of those cases involved manufacturers who were testing — just not testing effectively. The gap wasn’t effort, it was protocol design.

The USP <61>/<62> framework is well-established and, honestly, not that complicated to implement once a brand understands what the tests are doing and why. The challenge is that the supplement industry has a lot of brands who learned quality as they scaled, rather than building quality infrastructure first. If you’re in that position — growing quickly and realizing your microbial testing program has gaps — the fix is available. It just requires being honest about where the gaps are.

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Written by Nour Abochama, Vice President of Operations, Qalitex Laboratories. Learn more about our team

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Related from our network

• How FDA Audit Preparedness Intersects with Lab Data Integrity — Aurora TIC covers the regulatory consulting side of documentation and quality systems that support your microbial testing records.
• Supplier Qualification and Raw Material COA Verification for Herbal Ingredients — Ayah Labs specializes in raw material testing and supplier qualification programs for botanical supply chains.
• Canadian NHP Microbial Standards: How Health Canada Requirements Differ from USP — Androxa outlines the microbial testing expectations for natural health products seeking Canadian market authorization.