Rapid Detection and Typing of Strains ofMycobacterium aviumsubsp.paratuberculosisfrom Broth Cultures

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Abstract
A liquid culture followed by molecular confirmation was evaluated for potential to improve sensitivity and reduce time to diagnosis ofMycobacterium aviumsubsp.paratuberculosisinfection. Fecal samples from 240 animals from Ohio farms were assessed for presence ofM. aviumsubsp.paratuberculosisusing four different protocols: (i) sedimentation processing followed by inoculation on Herrold's Egg Yolk media (HEYM) slants (monitored biweekly up to 16 weeks), (ii) double centrifugation processing followed by inoculation on HEYM slants (monitored biweekly up to 16 weeks), (iii) liquid-solid double culture method using modified 7H9 broth (8 weeks) followed by subculture on HEYM slants (monitored up to 8 weeks), and (iv) liquid culture using modified 7H9 broth (8 weeks) followed by molecular assays for the presence of twoM. aviumsubsp.paratuberculosis-specific targets. The number of positive samples detected by each protocol was 37, 53, 65, and 76, respectively. Twenty-seven samples were positive by all four methods. Based on samples positive by at least one method (n= 81), the sensitivities for sedimentation processing, double centrifugation processing, liquid-solid double culture, and liquid culture followed by molecular confirmation were 46%, 65%, 80%, and 94%, respectively. Fingerprinting of the positive samples using two polymorphic (G and GGT) short sequence repeat regions identified varying levels of within-farm and between-farm diversity. Our data indicate that liquid culture followed by molecular confirmation can significantly improve sensitivity and reduce time-to-diagnosis (from 16 to 8 weeks) ofM. aviumsubsp.paratuberculosisinfection and can also be efficiently employed for the systematic differentiation ofM. aviumsubsp.paratuberculosisstrains to understand the epidemiology of Johne's disease.

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