Last updated on June 19th, 2021
Anaerobes are significant component of normal flora of humans especially in small and large intestine, and female genitourinary tract. They help us by supplying vitamins, digesting foods and by outcompeting bacterial pathogens by colonizing on body surfaces. They can also cause infections when they reach into sterile sites or when their numbers are increased disproportionately.
Gram stain is an important rapid tool for anaerobic bacteriology. All the specimens submitted for anaerobic culture should be examined by Gram-staining prior to culture. Gram-stain reveals the types and relative numbers of microorganisms and host cells present in the sample. Gram stain also serves as a quality control measure for the adequacy of anaerobic techniques. After the isolation of the bacteria, the clinical relevance of the isolate is determined by correlating with the initial Gram-stain.
Is there any modification of the Gram staining technique for the anaerobes?
Yes. We use the same standard gram stain procedure and reagents but the safranin counterstain is left on for 3 to 5 minutes. Alternatively, 0.5% aqueous basic fuchsin can be used as the counterstain.
What do positive gram stain and negative culture indicate?
Positive grams stain with negative culture report gives information regarding the adequacy of sample collection, transport, and also of culture methods used. This situation may come in the following mentioned conditions:
- Poor transport methods
- Excessive exposure to air during sample processing
- Inadequate types of media or old media, or
- Failure of the anaerobic system used (jar, pouch, and chamber) to achieve an anaerobic atmosphere.
- That microorganisms have been killed by antimicrobial therapy