Effect of Watering Trough Chlorination on Persistence of Mycobacterium avium subsp paratuberculosis

Continued increases in Johne's disease around the world suggest more information is needed to understand the mechanisms by which the causative agent, Mycobacterium avium subsp paratuberculosis (MAP), is spread among livestock on the farm site. Livestock watering troughs are frequented by all animals on a farm; they provide a moist, nutrient-rich environment for bacterial survival, and the trough basin provides a surface for bacterial adhesion (i.e., biofilm formation). The goal of this study was to determine whether addition of chlorine to trough water could prevent or reduce biofilms containing MAP on trough materials. MAP was inoculated into trough water containing normal trough water microbial flora. The concentration of MAP in biofilms on suspended 1.5 in x 0.6 in (3.8 cm x 1.5 cm) concrete, plastic, galvanized or stainless steel trough materials was evaluated. Chlorine (2 ppm) was added to the trough water on day 7, and then weekly for 70 days. The concentration of MAP in biofilms on the trough materials was measured using quantitative, real-time PCR to target the MAP-specific IS900 sequence in DNA extracts. Chlorination was most effective against MAP on galvanized steel and stainless steel trough materials (99% reduction (t99) in biofilmassociated MAP in 15 and 16 days, respectively). This value was two to four times higher for MAP in biofilms on plastic and concrete materials (t99 of 33 and 66 days, respectively). Differences in effectiveness of disinfection may result from higher pH (pH 8.23) in troughs with concrete materials and lower chlorine availability in troughs with plastic materials. These results suggest that the effectiveness of chlorine disinfection depends on trough material construction, pH, and chlorine availability. Optimization of disinfection protocols and elimination of biofilms on trough surfaces should reduce persistence of MAP in trough waters.