Growth and survival of M. paratuberculosis in murine macrophages. Resting J774 macrophages were infected with M. paratuberculosis at time zero. Infected lysates were harvested and plated in triplicate on HEYM slants at 0, 24, 48, 72, 96, 120, 144, and 168 hours postinfection. The results from three independent experiments are shown. All platings were performed in triplicate. Error bars denote standard deviation.