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

Abstract

Aims: Four chemical decontamination protocols for milk were compared with respect to mean percentage recovery of spiked Mycobacterium avium subsp. paratuberculosis, minimum detection limit and ease of application. Methods and Results: Raw milk spiked with 106 cfu M.a. paratuberculosis was decontaminated prior to culture by: (1) treatment with 0.75% (w/v) hexadecylpyridinium chloride (HPC) for 5 h; (2) and (3) Cornell methods employing brain heart infusion broth containing 0.75% (w/v) and 0.9% (w/v) HPC, respectively; and (4) a C18-carboxypropylbetaine (CB-18™) method. The 0.75% HPC method yielded the highest mean percentage recovery of M.a. paratuberculosis (28.7%) and was capable of detecting the lowest number of cells (30 cfu/40 ml). Conclusions: Treatment of milk with 0.75% HPC for 5 h was shown to be superior to the other methods for decontaminating milk prior to culture for M.a. paratuberculosis. Significance and Impact of Study: Certain chemical decontamination protocols are too harsh for application to milk. The 'best' decontamination protocol only recovered a fraction of the M.a. paratuberculosis cells present in a milk sample.