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This includes the study of strain colony morphology (homogeneity, size, shape, colour, opacity and texture of colonies) and microscopic observation (shape and cell size, mobility, etc.). The CECT also determines the Gram, catalase and oxidase for prokaryotic cells.

Necessary material

An active culture of the strain (petri dish or agar slant).


Cell morphology is studied by observation of a fresh sample, wet mounted on an optical microscope taken from a young culture grown on a plate or in liquid. This observation can determine not only cell shape but also cell size.

Colony morphology is analysed by observing triple seeding rows sown in the culture medium recommended for the strain.

The Gram value of cells is obtained by applying the 3% KOH technique (Buck, 1982)

The value of the catalase is obtained by applying the 10 vol. hydrogen peroxide technique (Cowan and Steel, 1982).

The oxidase test is applied to determine the presence of cytochrome C (Smibert and Krieg, 1994).



Buck JD. (1982). Applied and Environmental Microbiology p. 992-993 Vol. 44, No. 4

Cowan ST, Steel KJ (1982). Manual para la identificación de bacterias de importancia médica. México: C.E.C.S.A.

Smibert RM, Krieg NR (1994). Systematics. Phenotipe characterization. In Methods for General and Molecular Bacteriology, pp 625. Edited by P.Gerdhardt, R.G.E. Murray, W.A. Wood, N.R. Krieg.