Most bacteria are quite colourless and transparent and have a refractive index similar to that of the aqueous fluids in which they are suspended. Unless the diaphragm is carefully adjusted usually there is considerable difficulty in bringing the organisms into focus. Small size of bacteria can be seen with the ordinary light microscope unless the organisms are stained.Some staining techniques, such as the Gram and Ziel Neelsen stains, although of great diagnostic value because of their differential staining properties for specific bacteria, reveal little internal structure. Other such as Feulgen stain for nuclear bodies, demonstrates specific structure. HANGING DROP TECHNIQUE The techniques employed are meant for microscopic observation of living bacteria. The motility The study of bacterial morphology is performed in two ways: 1. Observing unstained cells live by hanging drop preparation. 2. Observing dead cells by making use of chemical nature of their unicellular,
Bacteria Present in Human Gastrointestinal Tract The microial flora in the GI tract of human infants begins establishment immediately after birth of child. Anaerobic bacteria can be recovered from fecal specimens after birth . The vaginal and fecal flora of the mother, and also the environment (air and food, for instance) are important sources of bacteria. Changes in the diet can modify the microbial composition in the colon . For example, infants fed breast milk have mainly Bifidobacteria in their gut, but infants fed formula have more complex microfl ora which are predominantly Bacterioides , Bifidobacteria , Clostridia and Streptococci In the GI tract the large intestine is the most colonized area and can harbor up to 10 12 bacteria per gram of waste contents with hundreds of species represented . The large intestine contains mostly strict anaerobes and they may be categorized as bacteria that are either harmful or benefi cial . The pathogenic effects of harmful ba