Detection and Confirmation of Mycobacterium avium subsp. paratuberculosis in Direct Quantitative PCR Positive Fecal Samples by the Manual Fluorescent MGIT Culture System

An efficient protocol for the manual fluorescent MGIT culture system combined with rapid confirmation of Mycobacterium avium subsp. paratuberculosis (MAP) growth in the broth culture was established and evaluated for the detection of viable MAP in direct quantitative PCR (QPCR) positive bovine feces. Manually detected fluorescence emissions from MGIT tubes were analyzed objectively using an open source software, ImageJ. For molecular confirmation of MAP growth, DNA samples harvested by simply boiling the broth, an inexpensive and time- and labor-saving DNA preparation method, yielded adequate results. The sheep strain of MAP required longer incubation time relative to the cattle strain, suggesting that the MGIT system may not support well the growth of ovine isolates as described previously. Of 61 direct QPCR positive bovine feces, the recovery rate of MAP in the MGIT system (62.3%) was significantly higher (P<0.05) than that using 7H10 agar-based slants (44.3%). The time to obtain a final result for fecal culture by the MGIT system was several weeks earlier compared to solid media. In MGIT culture positive samples, the time to detect fluorescence was correlated with the DNA quantity detected in fecal QPCR. As a positive result in the direct fecal QPCR test does not mean fecal excretion of viable MAP, bacterial isolation by fecal culture could be conducted to verify the QPCR result. For this purpose, the manual MGIT system is a sensitive and rapid culture method at least for bovine samples.