Methods of phenotypic identification of non-tuberculous mycobacteria

Abstract

Non-tuberculous mycobacteria (NTM) are composed of mycobacterial species other than the Mycobacterium tuberculosis complex. Initially thought to be mere contaminants when isolated from clinical specimens, literature is increasing by the day showing NTM as proven pathogens. Due to the difference in antimicrobial susceptibility of different species, it becomes imperative for the microbiology laboratory to identify them to the species level. Molecular methods are available for rapid and accurate identification, but in a resource limited nation, phenotypic methods, albeit time consuming, are of paramount importance. By means of this article, the authors intend provide a concise summary of the basic biochemical reactions which can be done to identify most commonly isolated NTM.

Keywords: Biochemical reactions; Non tuberculous mycobacteria; Phenotypic identification.

Fig. 1

Niacin accumulation test.

Fig. 2

Nitrate reduction test.

Fig. 3

High catalase test (≥ 45 mm).

Fig. 4

Low catalase test (< 45 mm).

Fig. 5

Tween-80 hyrolysis test.

Fig. 6

Citrate utilization test.

Fig. 7

Test for iron uptake from the medium (dark brown colonies).

Fig. 8

Urea hydrolysis test.

Fig. 9

Tellurite reduction test.