Anaerobes are a significant component of the normal flora of humans, especially in small and large intestines, and the female genitourinary tract. They help us by supplying vitamins, digesting foods, and by outcompeting bacterial pathogens by colonizing body surfaces. They can also cause infections when they reach 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 Gramstaining 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 it 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 a 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
Acharya TankeshwarHello, thank you for visiting my blog. I am Tankeshwar Acharya. Blogging is my passion. As an asst. professor, I am teaching microbiology and immunology to medical and nursing students at PAHS, Nepal. I have been working as a microbiologist at Patan hospital for more than 10 years.
Clinical Specimens for Anaerobic Culture
Sample from sites known to have anaerobes as part of the normal flora (eg mouth) is unacceptable for anaerobic culture.
Anaerobic infections: Etiology, Characteristics, Diagnosis
Anaerobic bacteria are part of the normal flora but can cause abscess formation and tissue necrosis when enter into sterile sites.