Biological Load Tests

Biological Load Tests

Biological indicators (BI) defined by ANSI / AAMI and ISO are test systems containing live microorganisms that provide a certain resistance to a particular sterilization process. A biological indicator provides information on whether the conditions required to kill a certain number of microorganisms for a given sterilization process are met and provides a level of confidence in that process. Endospores or bacterial spores are microorganisms mainly used in BIs. It is considered some of the hardest to kill. In addition, bacterial spores are selected for a specific sterilization process based on their known resistance to this process. For example, Geobacillus stearothermophilus spores show a high resistance to vapor and vaporized hydrogen peroxide and are therefore used in BIs following these sterilization processes.


Depending on the specific species, the biological indicators may be used for a variety of sterilization processes using steam, hydrogen peroxide gas, ethylene oxide and more.

Various factors such as operator experience, load preparation, and sterilizer status can affect the sterilization cycle. HRs provide a direct measure of the lethality of the process, and thus the use of BIs to routinely monitor sterilizers provides assurance of the effectiveness of the sterilization process.

HRs are typically used in process propulsion devices (PCDs) designed to represent the most demanding products routinely processed. A result of this defined challenge for BI shows that the sterilizer is effective in killing a large number of highly resistant bacterial spores and provides users with a level of assurance in the sterilization process.


A biological indicator is formed from a carrier material to which bacterial spores with a certain resistance to the sterilization process are applied. The carrier material is sealed in a glass envelope or a bottle. The BI is subjected to sterilization and then incubated under defined growth conditions to determine if any spores survive the process. If no sport survives, none grows and the test is a gateway. If growth is detected, the test fails.

AAMI ST79: 2013 According to 2, PCDs containing biological indicators should be used for routine monitoring of steam sterilization cycles at least weekly, preferably daily and at each load containing implants. Sterile Processing Department personnel must follow the manufacturer's instructions for proper placement of the PCD containing BI in the sterilizer. In addition to routine sterilizer monitoring, PCDs containing BIs are also used for other applications listed below:

Routine load of non-humid loads

Routine load of implant loads. AAMI ST79: 2013 recommends using a PCD with BI and Class 5 integration indicator. Sterile Processing personnel can also use a PCD with a BI and a Class 6 installation package. In both cases, loads containing implants should be quarantined until BI results are known, unless there is an emergency.

Qualification of sterilizers after installation, relocation, main repair, breakdown and sterilization

Periodic product quality assurance test

Regardless of the type of process or application, Sterile Processing personnel should always follow the manufacturer's instructions for use (IFUs) when using a biological indicator to monitor sterilization.


Biological indicators (within a PCD) are often used for routine monitoring, qualification and load monitoring of the steam sterilizer. Biological indicators are designed to show whether conditions during a steam (autoclave) cycle are sufficient to reach a specified level of microbial inactivation. For steam sterilization, BIs are typically used in PCDs and AAMI ST79: 2013 is recommended for weekly and preferably daily routine monitoring of sterilizers and at any load containing implants.