Dynamics of the In vitro Growing of Mycobacterium bovis from the Lungs of Vaccinated and Infected Mice

Abstract

Background: Bovine tuberculosis (bTB) is a disease primarily caused by Mycobacterium bovis. Currently, no commercial vaccines exist for controlling bTB, making the development of effective vaccine candidates and testing models a high priority. Mouse models are widely used in preclinical trials of anti‑TB vaccines. Determining the appropriate cultivation time to assess the mycobacterial load in animal organs or biological samples is crucial to establishing a reliable model that can accurately evaluate the effectiveness of a vaccine candidate. The aim of this study was to assess the growth dynamics and the appearance of colony‑forming units (CFUs) in lung homogenates from mice infected with M. bovis. We compared the CFU counts from vaccinated and challenged mice with M. bovis using data from a previous experiment. Methods: CFUs obtained from the lungs of vaccinated and M. bovis‑challenged mice of a previous experiment were registered at 3 and 4 weeks of culturing in solid media. The statistical analysis was performed with Kruskal–Wallis, followed by a Dunn’s multiple comparison test. Results: On analyzing the CFU dynamics from lung homogenates, we found that mice vaccinated with Bacillus Calmette–Guérin preserved stable CFU counts after 3 weeks of cultivation on a solid medium. In contrast, both the unvaccinated group and the group vaccinated with an attenuated M. bovis triple mutant strain reached their final CFU counts only after 4 weeks of culturing. Conclusion: These findings underscore the importance of prolonged follow‑up to accurately assess CFU counts, which are crucial for determining vaccine efficacy in trials.