• A new approach to improve positive results among smear-negative clinical specimens for acid-fast bacilli
  • Zahra safaeian layen,1 Razieh sadat Amirfakhrian,2 Hadi Farsiani,3 Zahra Meshkat,4 Mohammad Derakhshan,5 Ehsan Aryan,6,*
    1. Antimicrobial resistance research center, Mashhad University of Medical Sciences, Mashhad, Iran
    2. Antimicrobial resistance research center, Mashhad University of Medical Sciences, Mashhad, Iran
    3. Antimicrobial resistance research center, Mashhad University of Medical Sciences, Mashhad, Iran
    4. Antimicrobial resistance research center, Mashhad University of Medical Sciences, Mashhad, Iran
    5. Antimicrobial resistance research center, Mashhad University of Medical Sciences, Mashhad, Iran
    6. Antimicrobial resistance research center, Mashhad University of Medical Sciences, Mashhad, Iran


  • Introduction: Acid-fast bacilli (AFB) are a group of bacteria causing tuberculosis (TB), leprosy and non-tuberculosis mycobacterial (NTM) infections. Smear microscopy is the most simple widely used method to detect these bacteria. Although mycobacterial culture is the gold standard method for AFB detection, it is usually timeconsuming and labor-intensive approach. Since the sensitivity of smear microscopy ranges from 30% to 80%, a smear-negative result don’t rule out Mycobacterial related disease. The present study aimed to introduce a new approach for improving the sensitivity of smear microcopy and reducing the number of false-negative results among AFB smear-negative specimens submitted to the Laboratory of Tuberculosis, Ghaem University Hospital, Mashhad, Iran.
  • Methods: In our study, all smear-negative reported samples were collected from Dec 2023 to June 2024. Then, the remainder of each sample that previously homogenized and concentrated by Petroff’s method was transferred to a 1.5-ml microtube and further concentrated by centrifuging at 14000 rpm for 8 minutes followed by discarding the supernatant and keeping the pellet. Finally, the smears were prepared from the pellets and stained by Ziehl-Neelsen method to be microscopically examined for AFB.
  • Results: Among the 1500 smear-negative collected samples, we could detect 7 positive results.
  • Conclusion: This study showed that the sensitivity of smear microscopy for AFB detection can be improved by a simple dual concentration approach.
  • Keywords: Mycobacteria, AFB, Improved detection, Smear microscopy.