Paper I
Question
Anaerobic culture methods
Answer
Anaerobic culture methods create and maintain an oxygen-free (or very low oxygen tension) environment, needed to isolate and grow obligate anaerobic bacteria that are killed or fail to grow in the presence of atmospheric oxygen.
Methods:
- Anaerobic jar (McIntosh and Filde’s jar) — inoculated plates placed in an airtight jar; a gas-generating envelope combined with a palladium catalyst removes residual oxygen by combining it with hydrogen to form water; a methylene blue or resazurin indicator confirms anaerobiosis.
- Anaerobic chamber (glove box) — a sealed cabinet continuously flushed with oxygen-free gas (nitrogen, hydrogen, CO2), allowing inoculation, incubation, and examination entirely within an anaerobic atmosphere — the most reliable method.
- Robertson’s cooked meat (RCM) broth — a reducing liquid medium; meat particles consume oxygen and lower the redox potential, supporting anaerobic growth even without special apparatus.
- Reducing/pre-reduced media — media containing reducing agents (thioglycollate, cysteine) lowering the oxidation-reduction potential.
- GasPak system — a commercially available self-contained gas-generating system used within an anaerobic jar.
Specimen handling: requires appropriate collection (avoiding air exposure, e.g., needle aspiration rather than swab) and prompt transport in an anaerobic transport medium, since many anaerobes die rapidly on oxygen exposure.