An unexpected contamination in a CO2 incubator has occurred and it is time to figure out when a full decontamination procedure can be worked into your already over-booked schedule. Here are three key questions to ask to help you choose a CO2incubator that offers the most appropriate decontamination method for your needs.
For decades, wet heat and dry heat have been common decontamination methods for many CO2 incubators. Wet heat, by definition, is heat with a high humidity running at 90°C. Dry heat, in contrast, does not use humidity and can run at temperatures up to 180°C. For contaminating organisms that have a cell wall, these methods may reduce populations, but will not completely eliminate them. See the table below for an idea of what level of reduction in populations you can expect from both the wet and dry heat decontamination methods:
|Contaminant||Log Reduction (Dry Heat)||Log Reduction (Wet Heat)|
As technology improves, other decontamination methods have become popular alternatives to wet and dry heat. Some organisms, such as Bacillus subtilis and Staphylococcus aureus, are able to tolerate high heat environments and require alternative decontamination methods to achieve a complete kill. Among these, vaporized hydrogen peroxide (H2O2) has emerged as an efficient method that completely eliminates a wide variety of contaminants (including spores), rather than just reducing their numbers. However, vaporized H2O2 must be used at a sufficient concentration, or else it may not have the strength to breach the cell walls of certain contaminating microorganisms.
To confirm whether your CO2 incubator’s decontamination protocol will kill the types of contaminations you are most concerned about, ask your manufacturer for decontamination test reports that include the types of organisms tested.
When measuring the efficacy of a decontamination method, the term “log reduction” is commonly used to quantify the reduction of an organism’s population.
A log reduction, by definition, stands for a 10-fold (one decimal) or 90% reduction in numbers of live bacteria. Another way to look at it is: a 1-Log Reduction would reduce the number of bacteria 90%. This means, for example, that 100 bacteria would be reduced to 10, or 10 reduced to 1.
It is important to note that a log reduction does not translate to a complete kill; rather, it reflects a reduction in the numbers of contaminating organisms. Conventionally, a 6-log reduction is considered to be an effective decontamination, but in reality, a small number of microbes remain, posing a risk for future re-contamination of the incubator space.
In the case of a complete kill, no contaminating microorganisms remain, and swabs of previously contaminated areas will not grow when placed in culture media and incubated. If a contaminant is resistant to heat, or if a high enough concentration of vaporized H2O2 is not used, a complete kill is difficult to achieve.
It is easy to learn whether your CO2 incubator’s decontamination protocol produces a complete kill or a reduction in microbial population. Just ask your manufacturer for detailed decontamination test results, and critically examine the method(s) used to determine whether or not the decontamination was effective.
A third factor to consider when selecting a decontamination method is the time that it takes to be up and running again. Faster decontamination cycles enhance laboratory productivity, allowing for less downtime. Take a look at the table below to see the range of how long different decontamination methods take to complete:
|Decon Cycle Length|
|Wet Heat||At least 9 hours|
|Dry Heat||At least 8 hours|
|Vaporized H2O2||At least 3 hours|
Vaporized H2O2 is not only an effective method when used in high enough concentrations, but it is also one of the most efficient.
It is easy to be swayed by marketing literature that boasts about CO2 incubator decontamination methods that provide complete kills or log reductions, but being able to review the procedures that drive these claims is the only way to be confident about which method will be best for you and your lab. The three commercial methods commonly used within most CO2 incubators today (wet heat, dry heat, and vaporized H2O2) each have different characteristics and were developed to meet different needs. The method you select should be based on your assessment of the contamination you might experience (an organism more or less tolerant to high heat), the effectiveness that you desire (log reduction or complete kill), and threshold for downtime within the laboratory environment (3 hours or up to 14).
As always, before settling on a CO2 incubator and method of decontamination, we strongly advise that you perform a risk assessment of that method, as well as consult your biosafety officer to reasonably ensure you are in compliance with the standard operating procedures for your facility and the lab.
Cultivo®, the CO2 incubator from Baker, employs a vaporized H2O2 biodecontamination protocol that has been designed to achieve a complete kill for a wide variety of contaminating microorganisms, including spores, in less than 4 hours. For more information on the effectiveness of vaporized H2O2 as a CO2 incubator decontamination method, download our test report.