Isolation of Mycobacterium paratuberculosis from washed bovine ova after in vitro exposure

Summary To establish whether Mycobacterium paratuberculosis could be cultured from Dulbecco phosphate-buffered saline solution (dpbss) and to test 3 sampling methods, dpbss supplemented with 2% fetal bovine serum was inoculated with M paratuberculosis at concentrations of 104, 103, 102, 101, and 100 colony-forming units/ml. The inoculated media was sampled after mixing, after centrifugation, and after centrifugation and decontamination with 0.75% hexadecylpyridinium chloride. The samples were inoculated onto 3 slants of Herrolds egg yolk medium supplemented with sodium pyruvate and mycobactin J and 1 slant without mycobactin J. Mycobacterium paratuberculosis was isolated following all 3 sampling methods for all concentrations. Treatment with hexadecylpyridinium chloride decreased the number of colonies isolated. To test the efficacy of a 10-step wash procedure for removing M paratuberculosis from bovine ova, washed zona pellucida intact bovine ova were incubated in dpbss supplemented with 2% fetal bovine serum containing concentrations of 104, 103, 102, 101, and 100 colony-forming units of M paratuberculosis/ml for 12 hours at 22 C. Ten zona pellucida intact ova were removed from each concentration and washed by passing through 10 changes of dpbss supplemented with 15% fetal bovine serum. The media from each wash step was inoculated onto slants of Herrolds egg yolk medium. The ova were included with the tenth wash step. Mycobacterium paratuberculosis was isolated from 1 of 10 tenth-wash steps at the 104 concentration and 5 of 10 tenth-wash steps at 103.