Special anaerobic conditions must be achieved for the incubation of media plates to propagate anaerobic bacteria. Anaerobic conditions are met when 80 to 90% nitrogen (N2), 5% hydrogen (H2), and 5 to 10% carbon dioxide (CO2) is reached and maintained.
How is this achieved? Anaerobic conditions may be achieved by:
- production of a vacuum
- displacement of oxygen with other gases
- absorption of oxygen by chemical (or biological) means
- using reducing agents
Role of components:
- Gas mixture displaces oxygen.
- Palladium catalyst reacts with hydrogen gas to remove excess oxygen by forming water molecules.
- Vacuum airlock (used in chambers) reduces oxygen levels before transfer of items into the chamber.
- Sachet is composed of sodium bicarbonate and sodium borohydride. When water is added, hydrogen and carbon dioxide gas are produced.
- Indicator strip is composed of methylene blue (blue) or resazurin (pink) indicators. They become colorless when low concentrations of oxygen have been achieved.
- Some newer sachets do not require water or catalysts. The sachet contains inorganic carbonate, activated carbon, ascorbic acid, and water. (The indicator has been incorporated onto the outside.) Upon opening the outer wrapper, the proper environment is generated by exposure to air. Sachets are specific for anaerobic cultivation.
Several common methods of achieving anaerobic conditions include:
- Anaerobic gas-generating envelopes, bags, or pouches
- Anaerobic jar
- Anaerobic chamber glove box (an airtight box with attached gloves for manipulation of cultures within the anaerobic environment)
- An automated evacuation-replacement technique to control the gas mixture in the jars
Note: Some of these anaerobic concepts may also be found in special anaerobic collection swabs and specimen transport kits. These help provide an oxygen-free atmosphere when transport of the specimen may be delayed.
Quality control (QC) of anaerobic conditions:
Monitor and document QC daily (or when in use), to include:
- Temperature of the incubator holding the anaerobic jar or envelopes/bags/pouches, as well as any anaerobic chamber(s). Is the temperature in the expected range (35°C to 37°C)?
- Indicator strip - did it become colorless as expected? If using a biological indicator, did the organism(s) grow as expected?
- For anaerobic chambers, documentation of the humidity inside the chamber may be required.
- Cultures of known anaerobes may also be included in a quality control program.
Patient results should not be released until an investigation of any nonconforming event has been investigated and resolved. Fully document all corrective actions.
