Index >>Bacterial Classification>>Characters Used in Bacterial Identification

Bacteria also possess certain characteristic strctures such as the capsules, the flagella, the spores etc. Whose presence or absence is used as a tool indentification. The presence of capsules may be demonstrated by negative staining using India ink, nigrosin or by dark field microscopy some bacteria such as the bacilli and the clostridia form endos pores whose size, shape and position within the cell are characteristic of the species. By simple staining procedures the presence of these structures can be demonstrated. Special methods such as the Dorner method of spore staining using carbolfuchsin and nigrosin, allow the detection of spores more clearly. Vegetative cells of some bacteria such as the mycobacteria and Nocardia, are lipophilic and are difficult to stain but once stained with hot phenolic basic fuchsin solution, they are resistant to destaining by acid alcohol. Such bacteria are called as acid fast bacteria. Some bacteria possess flagella, the organ of motility. Their number, size, position etc., are characteristic of each organism. The presence of flagella cannot be detected easily although motility can be seen under a light microscope using a banging drop preparation. In order to see the flagella, it is necessary to increase their apparent diameter by first coating these structures with a mordant such as tannic acid and then applying one of the special stains such as the Leifson's stain. Care must be taken to use clean slides and young cultures for flagellar detection.