Optimisation of decontamination method and influence of culture media on the recovery of Mycobacterium avium subspecies paratuberculosis from spiked water sediments

Abstract

The recovery of Mycobacterium avium subspecies paratuberculosis (Map) from the environment can be a laborious process - owing to Map being fastidious, its low number, and also high numbers of other microbial populations in such settings. Protocols i.e. filtration, decontamination and modified elution were devised to recover Map from spiked water sediments. Three culture media: Herrold's Egg Yolk Media (HEYM), Middlebrook 7H10 (M-7H10) and Bactec 12B were then employed to grow the organism following its elution. In the sterile sediment samples the recovery of Map was significant between the time of exposure for each of HEYM and M-7H10, and insignificant between both media (P < 0.05). However, in the non-sterile sediment samples, the HEYM grew other background microflora including moulds at all the times of exposure whilst 4 h followed by M-7H10 culture yielded Map colonies without any background microflora. Using sterile samples only for the Bactec 12B, the recovery of Map decreased as time of exposure increased. Based on these findings, M-7H10 should be considered for the recovery of Map from the natural environment including water sediments where the recovery of diverse microbial species remains a challenge.

Significance of the study: Map is a robust pathogen that abides in the environment. In water treatment operations, Map associates with floccules and other particulate matter including sediments. It is also a fastidious organism, and its detection and recovery from the water environment is a laborious process and can be misleading within the abundance of other mycobacterial species owing to their close resemblance in phylogenetic traits. In the absence of a reliable recovery method, Map continues to pose public health risks through biofilm in household water tanks, hence the need for the development of a reliable recovery protocol to monitor the presence of Map in water systems in order to curtail its public health risks.

Keywords: Culture media; Decontamination; Mycobacterium avium subspecies paratuberculosis; Recovery method; Water sediments.