Comparative evaluation of the MGITTM and BACTEC culture systems for the recovery of Mycobacterium avium subsp. paratuberculosis from milk

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Abstract
Aims: To compare the detection capabilities of the non‐radiometric MGITTM (Mycobacteria Growth Indicator Tubes) and radiometric BACTEC 460TB culture systems (Becton Dickinson, Cowley, Oxford, UK) for recovering Mycobacterium avium subsp. paratuberculosis from milk. Methods and Results: Ultra heat treated (UHT) milk samples spiked with different levels of M. paratuberculosis (10–107 cells ml−1) were inoculated into MGIT and BACTEC media (containing recommended supplements) with and without prior chemical decontamination of the milk samples with 0·75% (w/v) cetylpyridinium chloride for 5 h. Time for the detection of growth in days was recorded for each culture system, and a M. paratuberculosis count for each milk sample was calculated from BACTEC readings using a published formula. Correlation between MGIT and BACTEC detection times was 0·6983. Both culture systems were capable of detecting 10–100 M. paratuberculosis cells ml−1 in milk within 30–40 days when no decontamination treatment was applied, but only 102–103 cells ml−1 or greater when chemical decontamination was applied before culture. Conclusions, Significance and Impact of Study: The non‐radiometric MGIT system could be substituted for the radiometric BACTEC system for the culture of M. paratuberculosis from milk without loss of detection sensitivity. Chemical decontamination before culture caused a significant reduction in numbers of viable M. paratuberculosis in all spiked milk samples resulting in decreased detection capability for both culture systems.

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