| Photomicrographs |
Section: MICROORGANISMS
Subsection: BACTERIA
Date Composed: 12-11-95 Date Modified: 12-19-95
Bacteria are microscopic organisms which when unstained are nearly transparent. Staining procedures are used to determine size, shape, arrangement, and other characteristics.
Bacteria may be rod or bacillus shaped. Incomplete division of rod-shaped bacteria may result in arrangements such as diplobacilli or streptobacilli. Short rods termed coccobacilli usually come in single arrangement. Aerobic sporeforming bacteria are often longer thicker rods, while anaerobic sporeforming bacteria usually are thinner and/or smaller rods. Bacteria can be partially characterized but not classified by their morphology. Very specific metabolic tests are used to identify individual species.
Round bacteria or cocci exist in many arrangements. Like the bacilli, a complete division results in single arrangements, while incomplete division results in arrangements such as diplococci, strepto-cocci (chains of cocci), staphylococci (grape clusters) and sarcinae (tetrads).
Bacteria also exist in many other shapes such as comma (vibrio) shaped and spirillum shaped.
Simple stains such as crystal violet and lactofuchsin are used to give definition to bacteria
whereas differential stains are needed to see capsules and some spores.
Bacteria have varied metabolic capabilities. Some are strictly aerobic or anaerobic while others are facultative anaerobes. Most use preformed organic molecules for carbon and energy while others use inorganic C02 for carbon and light or inorganic molecules for energy. Yet others use organic carbon as carbon source and inorganic molecules for energy.
Some bacteria produce endospores. This is a specialized structure which gives the cell resistance to environmental stresses. The actinomycete group of bacteria produce various asexual reproduc-tive spores. Generally, bacterial reproduction is asexual and occurs by binary fission resulting in identical daughter cells.
Many bacteria produce a capsule. This is generally mucoid in nature and consists of lipids and polysaccharides. The capsule provides protection for the organism in certain environments.
Suggested methods for slide preparation are: