In Vitro Visualization of Bacterial Colonies by Optical Coherence Tomography

Assessment of bacterial species in microbiology labs typically involves cultivating bacteria on solid media, where bacterial colonies form. Identification of strains depends on colony morphology, including surface color, size, edge shape, pattern, opacity, and shine. Yet, traditional methods cannot evaluate 3D morphology. Optical coherence tomography (OCT) acquires volumetric information by detecting backscattered light at different sample depths and enables quantitative determination of 3D morphology. In this study, colonies of five bacterial strains were imaged using an OCT system at 880 nm, with a lateral resolution of 2.2 μm, depth resolution of 1.4 μm, and an imaged area of 1.1 × 1.1 mm<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup>. Analysis of OCT images revealed differences in upper surface curvatures, lateral and axial dimensions, colony bottom shapes, and internal composition. OCT imaging demonstrates that bacterial strains exhibit distinct 3D morphology features, aiding differentiation. The technique also offers insights into internal colony structures, providing microbiologists with complementary data beyond traditional methods.