Biological indicators (BIs) confirm the effectiveness of sterilization processes within autoclaves. They provide direct evidence that equipment, such as medical instruments, is properly sterilized. Their use is considered the most reliable method for verifying sterilization conditions. This verification is essential for infection control and ensuring safety in healthcare and research environments.
What Are Biological Indicators
Biological indicators are test systems using viable microorganisms, typically bacterial spores, resistant to specific sterilization processes. For steam sterilization, Geobacillus stearothermophilus is commonly used due to its high resistance to heat and steam. These indicators usually come as spore strips or self-contained vials containing these spores and a growth medium.
A BI directly measures the sterilizer’s ability to kill highly resistant microorganisms, indicating sterilization success. This differs from chemical indicators, which only confirm exposure to sterilization conditions. After exposure to the sterilization cycle, the BI is incubated. A visual change, like a color change or turbidity in the growth medium, indicates if spores survived; no growth signifies a successful sterilization process.
Preparing and Running a Biological Indicator Test
Accurate test results depend on proper handling and preparation of biological indicators. Store BIs according to manufacturer instructions, typically at room temperature, away from sterilants. Before processing, include an unprocessed control BI from the same lot. This control confirms spore viability and proper incubation conditions.
Place the biological indicator in the coolest, most challenging area for steam penetration within the autoclave chamber. This location is often the bottom shelf near the drain in a steam sterilizer, or within the densest part of the load. For complex loads, use multiple BIs inside lumens or dense packs to effectively challenge the process. After placement, run the autoclave cycle according to manufacturer guidelines for both the sterilizer and items.
After the sterilization cycle, safely remove the processed BI and allow it to cool for 10-15 minutes before activation. For self-contained units, activation involves crushing an inner ampule to mix spores with the growth medium, ensuring contact with nutrients if they survived. Place the activated processed BI, along with the unprocessed control BI, in an incubator. Incubation for Geobacillus stearothermophilus is typically 55-60°C, with durations ranging from 24-48 hours for rapid-read indicators or up to 7 days for conventional ones, as specified by the manufacturer.
Interpreting Test Results and Troubleshooting
Interpreting BI test results involves observing incubated vials for bacterial growth. A “pass” result, indicating a successful sterilization cycle, shows no color change or turbidity in the processed BI. This confirms Geobacillus stearothermophilus spores were killed. Conversely, a “fail” result is a color change (often yellow) or turbidity in the processed BI, signaling spore survival and multiplication.
The unprocessed control BI must show growth (typically a color change) to confirm spore viability and suitable incubation conditions. If the control BI does not show growth, the validity of the entire test is compromised. If a BI test fails, immediate action is necessary. Take the sterilizer out of service, and quarantine and reprocess all instruments from the failed load.
Troubleshooting a positive BI result involves systematically investigating potential causes. This includes re-testing the sterilizer and reviewing operational procedures, like proper loading, to ensure effective steam circulation. Verify that the autoclave’s cycle parameters (temperature, pressure, time) were set and maintained correctly. Checking maintenance logs for recent issues or overdue servicing can provide insights. If failures persist, contact a service technician for further inspection or repair.
Frequency of Testing and Record Keeping
Routine BI testing is standard practice to ensure ongoing sterilization effectiveness. Guidelines recommend BI tests at least weekly, or once per 40 hours of autoclave use, and after any repair or maintenance. New autoclave installations or equipment relocations also necessitate immediate BI testing to confirm proper function.
Meticulous record-keeping for all BI tests is essential for quality assurance and compliance. Records should include the test date, cycle parameters, BI lot number, placement within the load, and final test results (including control BI). Document any actions taken in response to positive results, such as reprocessing loads or contacting service technicians. Maintaining these detailed records demonstrates adherence to regulatory standards and ensures the safety of sterilized items.