Importance of Gram Stain in Anaerobic Bacteriology

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:

  1. Poor transport methods
  2. Excessive exposure to air during sample processing
  3. Inadequate types of media or old media, or
  4. Failure of the anaerobic system used (jar, pouch, and chamber) to achieve an anaerobic atmosphere.
  5. That microorganisms have been killed by antimicrobial therapy

About Acharya Tankeshwar 474 Articles
Hello, thank you for visiting my blog. I am Tankeshwar Acharya. Blogging is my passion. I am working as an Asst. Professor and Microbiologist at Department of Microbiology and Immunology, Patan Academy of Health Sciences, Nepal. If you want me to write about any posts that you found confusing/difficult, please mention in the comments below.


    • Ivana
      If any sample contains “anaerobic bacteria”, in Gram stainining you will be able to see them but those organisms wont grow in routine culture media (as they needs anerobic condition for growth), so the culture will be negative.

  1. good explanation , i wish to know if we can do pour plate method for oral infections for isolating microorganisms form dental plaque materials can you explain the way of organisms to be gor from pour plate method to demonstrate to a UG

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