Lack of mycobactin dependence of mycobacteria isolated on Middlebrook 7H11 from clinical cases of ovine paratuberculosis.

Mycobacterium avium subsp. paratuberculosis is distinguished from other mycobacterial species by its dependence on the iron-chelator factor mycobactin and its prolonged incubation period when grown in vitro. Traditionally, a very low rate of isolation has been considered characteristic of sheep strains of this mycobacterium species. In the present study, a comparison was made of the performance of two media, Löwenstein-Jensen and Middlebrook 7H11/OADC both with and without mycobactin, on the isolation of M. a. paratuberculosis from ovine cases of the disease. A high isolation rate in both media was observed. Moreover, our results indicated that mycobactin dependence of sheep strains of M. a. paratuberculosis is medium related, being dependent on Löwenstein-Jensen and independent on Middlebrook 7H11/OADC.