Compliance, Sterilization

Understanding Biological Indicators and Spore Testing in Dental Sterilization

September 22, 2026

Key Takeaways

Biological indicators, commonly called spore tests, use highly resistant bacterial spores to evaluate the effectiveness of a sterilization process.
Biological monitoring is one part of a complete sterilization monitoring program and should be considered alongside mechanical and chemical monitoring.
Spore testing procedures and required frequency can vary depending on jurisdiction, sterilizer type, cycle, and manufacturer instructions.
A control biological indicator helps confirm that the testing system and incubation process are functioning properly.
A positive biological indicator requires investigation, but the result alone does not explain why the sterilization process failed.
Dental practices should maintain clear biological monitoring records so results can be connected to the appropriate sterilizer, cycle, load, and corrective actions.

Introduction

A sterilizer can complete its cycle without displaying an error. The expected time, temperature, and pressure may be reached, and the chemical indicators may respond appropriately. Those checks provide valuable information about the cycle, but they do not directly challenge the sterilization process with microorganisms.

That is where biological monitoring comes in. Often called spore tests, these indicators contain highly resistant bacterial spores and are used to evaluate whether a sterilization process was capable of destroying microorganisms that are intentionally more difficult to kill than those normally expected on contaminated instruments.

For dental practices, biological monitoring is not simply another test to add to a sterilization log. It is part of a broader quality assurance process that helps the team understand whether sterilization equipment and procedures are performing as intended. Knowing how biological indicators work, how their results should be interpreted, and how they fit alongside other monitoring methods can make that process much easier to manage consistently.

What Is a Biological Indicator?

A biological indicator contains bacterial spores selected because they are highly resistant to a specific sterilization method. In steam sterilization, for example, biological indicators commonly use spores of Geobacillus stearothermophilus. If a properly processed biological indicator shows that those resistant spores have been inactivated, it provides strong evidence that the sterilization process delivered sufficient microbial killing conditions.

This is what separates biological monitoring from simply confirming that the sterilizer reached a certain temperature or completed a programmed cycle. Mechanical monitoring measures physical conditions such as time, temperature, and pressure, while chemical indicators respond to exposure to one or more sterilization conditions. Biological indicators go one step further by challenging the process with living microorganisms.

That does not mean a spore test should be viewed in isolation. A reliable sterilization monitoring program brings together biological, mechanical, and chemical information because each method provides a different piece of evidence about the cycle.

How Biological, Mechanical, and Chemical Monitoring Work Together

Mechanical monitoring helps verify that the sterilizer reached its intended physical parameters. Depending on the equipment, this may include reviewing time, temperature, pressure, cycle displays, printouts, or electronic records. Because this information is available during or immediately after the cycle, it can provide an early indication that something did not perform as expected.

Chemical indicators provide another layer of monitoring. They are designed to react when exposed to specific sterilization conditions and can help identify problems such as inadequate exposure or sterilant penetration. The exact type and placement of chemical indicators depends on the sterilization process, packaging system, applicable guidance, and manufacturer instructions.

Spore tests serve a different purpose because they directly evaluate the microbial killing effectiveness of the sterilization process. These methods complement one another rather than compete with one another. A strong monitoring program uses the information collectively to create a more complete picture of how the sterilization process is performing.

This broader approach also supports the principles behind Sowingo’s article on sterilization changes under CSA Z314:23, which looks at monitoring as part of a complete reprocessing and quality assurance system rather than an isolated task.

How Does a Spore Test Work?

The exact process depends on the indicator, sterilizer, cycle, and manufacturer instructions, but the basic concept is straightforward. A spore test is placed in the sterilizer in a location or process challenge device (PCD) designed to represent a particularly difficult condition for the sterilization process to reach. The sterilizer then completes the intended cycle, after which the indicator is incubated and evaluated according to the test manufacturer’s instructions.

The processed test is normally evaluated alongside an unprocessed control from the same lot. The control does not go through the sterilizer. Instead, it is incubated separately to demonstrate that the spores were viable and that the incubation system was capable of detecting growth.

If the processed indicator shows no growth while the control behaves as expected, the result supports the conclusion that the sterilization process successfully inactivated the test organisms. If the processed indicator shows growth, the result requires investigation because viable spores remained after the sterilization process.

The details matter. Using the correct indicator, placing it properly, choosing the appropriate cycle, incubating it according to instructions, and recording the result all contribute to the reliability of the test.

Why the Control Biological Indicator Matters

It can be tempting to focus entirely on the test that went through the sterilizer, but the control provides important context for interpreting the result. Without a functioning control, the practice may not know whether an apparent negative result reflects successful sterilization or a problem with the indicator or incubation process.

For example, imagine that the spores in a biological indicator were no longer viable before testing. The processed test could appear negative even if the sterilization process itself was inadequate. A valid control helps demonstrate that the organisms were capable of growth and that the test system was functioning correctly.

This is why biological monitoring should be treated as a complete process rather than a single item placed in an autoclave. The test, control, incubation process, interpretation, and documentation all work together.

How Often Should Dental Practices Perform Spore Testing?

There is no single testing frequency that every dental practice in Canada and the United States should assume applies to them. Requirements and recommendations may vary depending on the jurisdiction, sterilization method, equipment, cycle type, type of item being processed, and manufacturer instructions.

In the United States, the CDC recommends using a biological indicator at least weekly to monitor sterilizers and for every load containing an implantable device. Canadian requirements are generally established through provincial or territorial standards, regulators, public health guidance, and other applicable requirements, which means practices may encounter different testing frequencies depending on where they operate.

The important point is not to memorize one universal schedule. Each practice should identify which requirements apply to its location and equipment, confirm those requirements against the sterilizer and biological indicator manufacturers’ instructions, and incorporate the resulting schedule into its written reprocessing procedures.

This approach also makes training easier. Rather than relying on staff to remember an informal routine, the practice has a defined biological monitoring process that reflects the requirements that actually apply to it.

What Does a Negative Spore Test Mean?

A negative spore test means that the resistant spores contained in the processed test were inactivated during the sterilization process. Because these organisms are deliberately selected for their resistance, that result provides strong evidence about the microbial killing effectiveness of the cycle.

However, a negative biological result does not make the other elements of sterilization monitoring unnecessary. The practice should still review the required mechanical and chemical monitoring information and confirm that the complete reprocessing procedure was followed correctly.

This is an important distinction because sterilization depends on more than the sterilizer itself. Cleaning, inspection, packaging, loading, cycle selection, monitoring, handling, storage, and staff procedures all influence the reliability of the overall process.

What Does a Positive Biological Indicator Mean?

A positive spore test means that viable test spores were detected after the sterilization process. The result needs to be taken seriously, but it does not automatically identify the cause. Potential contributing factors can include incorrect loading, inappropriate cycle selection, problems with steam delivery, testing errors, packaging issues, incorrect sterilizer operation, or equipment malfunction.

The next step is therefore investigation rather than assumption. The practice should follow its written corrective action procedure, the sterilizer and biological indicator manufacturers’ instructions, and any applicable regulatory or public health guidance. Mechanical readings, chemical indicator results, load information, testing procedures, maintenance records, and recent biological monitoring history may all help determine what happened.

The appropriate response can also depend on the circumstances and sterilization method. Sowingo’s article on what to do after a failed sterilization test provides a broader framework for reviewing affected loads, investigating the reprocessing workflow, documenting corrective action, and determining when equipment can safely return to service.

Why Biological Monitoring Records Matter

A spore test result becomes much more useful when the practice can connect it to the appropriate sterilizer, cycle, load, date, and surrounding monitoring information. If an unexpected result occurs, staff need enough documentation to reconstruct what happened and determine what may have been affected.

That record may include the test and control results, sterilizer identification, cycle information, mechanical monitoring data, chemical indicator results, maintenance information, and any investigation or corrective action that followed. The specific documentation requirements and retention periods may vary by jurisdiction, so practices should confirm what applies locally.

Organized records support more than regulatory compliance. They make it easier to identify patterns, investigate unexpected results, review equipment history, and demonstrate that the practice has a consistent process for responding when something goes wrong.

This is also where documentation can become vulnerable in a busy practice. Sowingo’s article on why sterilization documentation breaks down explores how delayed entry, disconnected records, and reliance on memory can gradually create gaps even when staff understand the importance of documentation.

Build Biological Monitoring Into the Everyday Workflow

Biological monitoring is most reliable when it is treated as a routine part of instrument reprocessing rather than a separate compliance task. Staff should understand which indicators are used with each sterilizer, where they are placed, how controls are handled, who is responsible for reviewing the results, and where the information is recorded.

Those expectations should be included in written procedures and staff training. A new team member should not have to learn spore testing simply by watching how someone else happens to perform it that day. Standardized procedures, manufacturer instructions, hands-on training, and competency review help make the process more consistent across the team.

Sowingo’s guide on training new staff on sterilization procedures looks at this same principle more broadly. The goal is not to remove professional judgement from the process, but to make sure every team member is working from the same documented expectations.

Follow the Requirements That Apply to Your Practice

Sterilization principles are broadly shared across dental practices, but regulatory requirements are not identical everywhere. Canadian provinces and territories, US states, local authorities, professional regulators, and public health organizations may establish different requirements for monitoring frequency, documentation, record retention, equipment testing, and responses to failed indicators.

Manufacturer instructions add another layer. The sterilizer, biological indicator, packaging system, and reusable instruments may each include validated instructions that affect how the reprocessing process should be performed.

For that reason, general educational guidance should never replace the requirements that apply to the individual practice. A strong sterilization program combines broadly accepted infection prevention principles with current local requirements and the manufacturer’s instructions for the equipment and products being used.

How Sowingo Helps Dental Practices Manage Sterilization Records

Spore testing produces records that need to remain organized alongside the rest of the practice’s sterilization documentation. When cycle information, test results, maintenance documents, and corrective actions live across separate paper logs or disconnected files, reviewing the history of a sterilizer can become unnecessarily difficult.

Sowingo’s Sterilization and Compliance software allows dental teams to digitally organize sterilization testing and cycle documentation in one place. Centralized records can make it easier to review past results, maintain a consistent documentation process, and retrieve information when the practice needs to investigate an unexpected result or respond to a regulatory review.

Digital documentation does not replace correct sterilization procedures, manufacturer instructions, or regulatory responsibilities. It supports the people responsible for those processes by making the information surrounding them easier to record, organize, and access.

Conclusion

Spore testing gives dental practices direct evidence about the microbial killing effectiveness of a sterilization cycle. Its value is strongest when the result is considered alongside mechanical and chemical monitoring rather than treated as a stand-alone check.

A reliable program also depends on consistent technique: using the appropriate test, following manufacturer instructions, maintaining a valid control, documenting results clearly, and applying the requirements that govern the practice’s location and equipment.

Built into the everyday reprocessing workflow, biological monitoring becomes a practical quality assurance tool that helps teams recognize problems, investigate unexpected results, and maintain confidence in their sterilization process.

Frequently Asked Questions

What if the control does not show the expected growth?

If the unprocessed control does not behave as expected, the test may not be valid because the practice cannot confirm that the spores were viable or that the incubation system was functioning properly. Follow the biological indicator manufacturer’s instructions for interpreting the result and repeating the test when required.

Does a negative spore test mean every instrument is sterile?

A negative biological indicator provides strong evidence that the sterilization process successfully inactivated the resistant spores in the test. It should still be interpreted alongside the required mechanical and chemical monitoring information and confirmation that the complete reprocessing process was followed correctly.

How often should a dental practice perform spore testing?

Testing frequency can vary by jurisdiction, sterilization method, equipment, and the types of items being processed. Practices should follow applicable provincial, territorial, state, or local requirements together with the sterilizer and biological indicator manufacturers’ instructions.

Why is a control biological indicator needed?

The unprocessed control demonstrates that the spores were viable and that the incubation system was capable of detecting growth. This gives the practice a valid comparison when interpreting the processed biological indicator.

What should a dental practice do after a positive biological indicator?

The practice should follow its written corrective action procedure, applicable regulatory guidance, and manufacturer instructions. The response may include reviewing the cycle and monitoring records, identifying affected loads, repeating testing, removing the sterilizer from service, arranging equipment inspection or repair, and documenting the investigation depending on the circumstances.

Should spore test records identify the specific sterilizer and cycle?

Yes. Records should make it possible to connect the result to the sterilizer and relevant cycle or load so the practice can reconstruct what happened if an unexpected result occurs. The exact documentation requirements and retention periods vary by jurisdiction.