- Top of page
- Materials and methods
- Bacterial strain and culture conditions
- Comparison of the detection limits and detection times for BACTEC and MGIT culture
- Comparison of the performance of BACTEC and MGIT culture systems when chemical decontamination was applied to milk before culture
- Statistical analysis of results
- Detection capabilities of MGIT and BACTEC culture systems with and without chemical decontamination
- Characterization of the relationship between MGIT detection times and log10 numbers of M. paratuberculosis
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.