Digital Semi-quantitative Colony Counting on Sector Plates: Repeatability Across Inoculum Levels (candida Albicans)
Year: 2026
Type: article
Abstract: Objective: This study aimed to evaluate the repeatability of a semi-quantitative digital growth metric for colony counting on sector plates and to determine its practical working range using a Candida albicans model. Methods: A 24-hour culture of C. albicans grown on meat-peptone agar was standardized to 0.5 McFarland units. Serial dilutions were prepared to achieve initial inoculum levels of 10⁰, 10², 10⁴, 10⁶, and 10⁸ CFU/mL. Sectoral seeding (100 µl) was performed on meat-peptone agar plates, followed by ncubation at 37°C for 24 hours (three independent replicates per level). Digital counting was performed using automated image recognition with the Scan 500 automatic colony counter (software version 6.3.8.0; Interscience, Saint Nom-la-Bretèche, France) in "Total Count" mode with fixed processing parameters. Non-microbial artifacts were manually removed to ensure count accuracy. The primary dependent variable was the U-metric, defined as the operator-corrected number of recognized colonies. Results: The distributions of the U index differed significantly across initial load levels (Kruskal-Wallis H-test, p=0.012). Repeatability was range-dependent: low levels exhibited zero values and high variability (CV: 173.2% for 10⁰ and 102.4% for 10²), while the 10⁴-level showed minimal variance (CV: 6.1%). At high ranges, the relationship between the U-metric and nominal load was non-monotonic. The number of artifacts removed by the operator ranged from 0 to 99 per plate. Conclusion: The U-metric serves as a standardized digital count – combining fixed recognition settings with operator correction – suitable for "control vs. experiment" comparisons using a consistent protocol. For this specific model, the practical working range was approximately 10⁴ CFU/mL. Keywords: Candida albicans, microbial colony counting, automated image processing, reproducibility, microbiological techniques, culture methods.
Source: Avicenna Bulletin
Institutions: Russian Academy of Sciences, Institute of Biomedical Problems
Language: Russian
Subfield: Biophysics
Domain: Life Sciences
Open Access status: diamond
OpenAlex ID: W7203610680