Comparative evaluation of four decontamination protocols for the isolationof Mycobacterium avium subsp paratuberculosis from milk

Aims: Four chemical decontamination protocols for milk were compared with r espect to mean percentage recovery of spiked Mycobacterium avium subsp. par a tuberculosis, minimum detection limit and ease of application. Methods and Results: Raw milk spiked with 10(6) cfa M.a. pa ra tuberculosis was decontaminated prior to culture by: (1) treatment with 0-75% (w/v) hex adecylpyridinium chloride (HPC) for 5 h; (2) and (3) Cornell methods employ ing brain heart infusion broth containing 0-75% (w/v) and 0.9% (w/v) HPC, r espectively; and (4) a C-18-carboxypropylbetaine (CB-18 (TM)) method. The 0 -75% HPC method yielded the highest mean percentage recovery of M.a. pa ra tuberculosis (28.7%) and was capable of detecting the lowest number of cell s (30 cfu/40 ml). Conclusions: Treatment of milk with 0.75% HPC for 5 h was shown to be super ior to the other methods for decontaminating milk prior to culture for M.a. pa ra tuberculosis. Significance and Impact of Study: Certain chemical decontamination protocol s are too harsh for application to milk. The 'best' decontamination protoco l only recovered a fraction of the M.a. paratuberculosis cells present in a milk sample.