The use of spiral plating and microscopic colony counting for the rapid quantitation of Mycobacterium paratuberculosis

Abstract

Aims: To evaluate a spiral plating and microscopic colony counting technique to hasten the quantitation of Mycobacterium paratuberculosis.

Methods and results: Broth and milk cultures of M. paratuberculosis were spirally plated onto Middlebrook agar plates and microscopically counted at 8 and 14 days of incubation. The same plates were recounted at 27-28 days of incubation when grossly visible colonies were present. The results were statistically compared with no difference in CFU ml-1 derived from the shorter vs longer incubation times. Other mycobacteria isolates were also plated and microscopically examined and found to be easily distinguishable from M. paratuberculosis.

Conclusions: Microscopic quantitation of spirally plated M. paratuberculosis cultures can be achieved within 8-14 days of plate incubation and compare favourably to counts derived after prolonged incubations.

Significance and impact of the study: The technique could greatly hasten the quantitation of viable M. paratuberculosis.