Genus-Level ID and USP 1113: What Compounding Pharmacies Need to Know

If you work in the pharmaceutical industry, you already know that no single USP chapter stands on its own. USP 797 sets expectations for sterile compounding to preserve patient safety and product efficacy, but it leans on other chapters, monographs, and general notices to address some of the details. For compounding pharmacies, USP 1113 provides the technical foundation for the genus-level identification required by USP 797. In this post, we’ll go through the relationship between USP 1113 and how it supports genus-level identification in USP 797.

What is USP 1113?

USP <1113> (Microbial Characterization, Identification, and Strain Typing) is a United States Pharmacopeia general information chapter that outlines principles and methods for identifying microorganisms recovered from pharmaceutical environments and products. It describes different identification approaches and gives a framework for verifying and selecting appropriate microbial ID techniques and laboratories.

You might think of USP 1113 as a “supporting actor.” That is, it isn’t a standard that compounding pharmacies follow directly. Rather, it provides the scientific backbone for microbiological expectations in multiple USP chapters, including USP <61> (Microbiological Examination of Nonsterile Products: Microbial Enumeration Tests), USP <62> (Tests for Specified Microorganisms), USP <71> (Sterility Tests), and USP <1116> (Microbiological Control and Monitoring of Aseptic Processing Environments), and of course USP <797>.

Instead of restating what is expected in each of these chapters, these chapters can simply point to USP 1113 for the relevant details. This standardization of expectations dramatically simplifies compliance. Because chapters are typically written by different committees, the absence of a common reference like USP 1113 could leave facilities subject to multiple standards trying to reconcile conflicting microbiology expectations.

Before we move on to discussing the relationship between USP 1113 and USP 797, it’s important to note that revisions to USP 1113 were open for public comment as recently as late 2025. These proposed updates are intended to modernize and clarify expectations around microbial characterization and identification, but the USP Microbiology and Sterility Assurance Expert Committee has not yet indicated whether the draft language will be adopted as is, further revised, or postponed. Given the uncertainty around these proposals, this post will focus on the official version that is currently in force.

USP 1113 References in USP 797

USP 797 references USP 1113 in both sections that require sample results exceeding an established action level to attempt to identify all recovered microorganisms to at least the genus level. For reference, here is the relevant language:

6.2.3 Viable air sampling data evaluation and action levels…If levels measured during viable air sampling exceed the levels in Table 7, an attempt must be made to identify any microorganisms recovered to the genus level (see Microbial Characterization, Identification, and Strain Typing <1113>.) with the assistance of a microbiologist.

6.3.3 Surface sampling data evaluation and action levels… If levels measured during surface sampling exceed the levels In Table 8, an attempt must be made to identify any microorganism recovered to the genus level (see <1113>.) with the assistance of a microbiologist.

While USP 797 only requires genus-level identification when there is an excursion, it’s important to remember that, as a compendial standard, this is a minimum expectation. State boards of pharmacy and local accrediting bodies may go further by requiring species-level identification or identification of all CFU recovered. For example, in Massachusetts, USP <797> compliance requires species-level identification of any microbial growth detected in ISO Class 5, ISO Class 7, or action-level-exceeding areas. Massachusetts Board Policy 2023-09 mandates identifying even a single colony-forming unit (CFU), with a microbiologist conducting a full profile and risk assessment. In addition, an individual pharmacy may choose to require genus-level identification in its own SOPs, based on its internal risk assessments and quality objectives.

What is Genus Level and Why Does It Matter?

USP <1113> covers a range of methods that can support genus-level ID, while also being capable of going to species or strain when needed. As most of this audience knows, genus is the taxonomic level just above species. For example, with the bacterium Staphylococcus aureus, Staphylococcus designates the genus, and aureus designates the species. In other words, S. aureus is just one species within the larger Staphylococcus genus.

In earlier posts, I’ve argued that genus is the minimum practical level of identification for environmental monitoring and investigations. The purpose of genus-level identification is all about knowing what kind of organism you’re dealing with in a way that is meaningful for risk assessment and response. Knowing the genus lets you classify the organism’s general behavior, including typical habitats, likely routes of entry, and broad clinical or product quality concerns, so you can trend it over time and decide whether your engineering controls and personnel competency protocols are working as intended.

That does not mean species never matters. In fact, there are situations where species-level identification is critical. For example, distinguishing S. aureus from coagulase-negative Staphylococcus when you are evaluating patient risk. S. aureus is a well-recognized pathogen associated with serious infections and higher morbidity and mortality, so detecting it in your facility can dramatically change how you assess risk and urgency.

Coagulase-negative staphylococci, by contrast, are often part of the normal skin flora and may represent either low-grade pathogens or simple contaminants, depending on the context and the specific species involved. If your report only says “Staphylococcus species,” you lose that distinction—and with it, a lot of the nuance you need to decide whether you are looking at a life-threatening exposure that demands aggressive action or a less concerning finding that can be managed with routine controls.

Which ID Method Does USP 1113 Require?

USP 1113 does not specify a single required microbial identification method. Instead, it acknowledges the full toolbox of microbial ID options—from classic bench tests and microscopy to biochemical panels and protein‑profiling systems like MALDI‑TOF. This lack of specificity empowers trained microbiologists to select the right tool for each scenario: a faster, more affordable method when genus‑level ID is sufficient or more advanced sequencing when additional resolution is truly needed

Since the science of microbial identification continues to evolve, this flexibility also leaves room for the pharmacy and its laboratory partner to choose methods that are scientifically sound, without being locked into a technology that could become obsolete before the next revision cycle.

Verifying Your Laboratory Partner

USP 1113 offers practical guidance on what you should expect from a laboratory that performs microbial identification on your behalf. Your responsibility is to confirm that the lab can actually meet that standard. At a high level, you want a partner that uses methods appropriate for the level of identification you need, understands the limitations of those methods, and has demonstrated that they can produce accurate, reproducible results for the types of organisms your facility might detect.

Of course, you are not just taking their word for it. The laboratory should be able to show you proof that the identification methods they use work as intended. They should be able to demonstrate that they have tested a defined set of organisms (including ones similar to those you encounter), compared their results to a trusted reference method or reference lab, and shown that their systems produce accurate, reproducible genus (and when needed, species) identifications. They should be able to document accuracy rates, explain how they handle difficult organism groups, and demonstrate that they use appropriate quality‑control strains.

A good lab should also be able to explain the principles behind its primary ID platforms and describe how databases are maintained and updated. In addition, the lab should be able to show that reagents, instruments, and software are qualified and routinely checked for suitability. ISO 17025—the international standard for testing and calibration laboratories—requires exactly this sort of control over equipment, methods, and records. Accreditation under ISO 17025 means an independent body has evaluated the lab’s quality system, equipment management, method validation/verification, staff competence, and data integrity, and confirmed that they meet the standard for the specific tests listed in their scope.

In practice, ISO 17025 accreditation gives you objective evidence that the lab’s processes for equipment qualification, calibration, reagent control, and record‑keeping are not just promises but have been audited against a recognized benchmark. When you are choosing a lab partner for microbial identification, asking for their ISO 17025 certificate (and scope) is a straightforward way to confirm many of the details.

Finally, USP 1113 implies that a competent lab partner will help you interpret results, not just generate them. The chapter stresses reviewing identifications for “reasonableness” against colony morphology, source, and growth characteristics, and it notes that some organisms may only be reliably reported to genus. When you evaluate a lab, look for microbiologists who will discuss borderline calls, explain when only genus‑level ID is appropriate, and collaborate on method selection and troubleshooting—rather than simply sending you an automated printout with no context.

Does Your Laboratory Measure Up?

If there’s one takeaway here, it’s this: You don’t have to become a microbiologist to meet the microbiology expectations in USP 797, but you do need to know how to choose the right laboratory partner. If you’re looking at your current environmental monitoring program or lab contract and wondering whether it truly lines up with the expectations outlined in USP 1113, that’s a good sign it’s time for a deeper look. Reach out to me, and let’s continue the conversation.