Establishment of a rapid and simple evaluation system for disinfectant efficacy against Mycobacterium avium subsp. paratuberculosis using a visual time-to-detection based liquid culture system.

Evaluating disinfectant efficacy against Mycobacterium avium subsp. paratuberculosis (MAP) requires culture-based methods. We established a simple, rapid liquid culture system using visually determined fluorescence time-to-detection (TTD), whereby a strain-specific standard curve enabled reliable estimation of MAP colony-forming units (CFU) for TTD values of 3-35 days. In sodium dichloroisocyanurate disinfection tests, CFU estimates obtained by liquid and solid culture differed by <10¹, whereas qPCR detected MAP DNA in culture-negative samples, highlighting the importance of viability-based assessment. Although MAP in spiked feces may be more directly exposed to disinfectants than in naturally infected feces, MAP-spiked feces provide a practical model for screening disinfectants under on-farm conditions. This system facilitates efficient evaluation of disinfection strategies for Johne's disease control.