Bacteria One of our kingdoms
Bacteria • Bacteria are minute microscopic prokaryotes. They are unicellular organisms, which are usually identified by their specific activities, more than their general organization. • Bacteria are omnipresent, occurring in all environments. • The average size of bacterial cell ranges from 0.2 to 2.0 µm.
Different Forms of Bacteria Cocci(singular coccus) • They are spherical in shape. They can be further distinguished into • Monococcus (occur singly) • Diplococcus (occur in pairs) • Tetracoccus (occur in groups of four) • Streptococcus (occur in the form of a filament) and • Staphylococcus (occur in the form of sheets).
Streptococcus pyogenes Responsible of common infections including "strep throat" and skin infections
Bacillus (Rl- bacilli) • They are straight, cylindrical, rod shaped bacteria. They may be further distinguished into • Monobacillus (single) • Diplobacillus (in pairs) • Streptobacillus (in filamentous form) and • Palisade Bacillus (in the form of a stack)
Bacillus anthracis anthrax— a common disease of livestock and, occasionally, of humans.
Spirillum • These bacteria are spirally coiled like a corkscrew. Lyme disease is caused by spirochetal bacteria from the genus Borrelia.
Vibrio • These are elongated, C shaped or comma shaped bacteria. Vibrio cholerae is a Gram-negative the cause of the cholera disease.
Flagellation • Most of the bacteria contain one to many locomotor structures called flagella. Cocci do not have flagella. Based on the number and mode of attachment of the flagella, bacteria can be distinguished into the following types: • I . Atrichous : Bacteria without flagella. II. Trichous: They bear one or more flagella. • a) Monotrichous : Bacteria with a single flagellum, at one end b) Cephalotrichous : Bacteria with many flagella attached at one end • c) Amphitrichous : Bacteria with a single flagellum at each end d) Lophotrichous : Bacteria with a group of flagella attached at each end • e) Peritrichous : Bacteria with flagella all over the body
Gram Positive and Gram Negative Bacteria • In 1884 a Danish physician Christian Gram devised a technique of differential staining for bacterial cells, using two simple stains. The procedure involves staining bacteria initially with a weak alkaline solution of gentian (crystalline) violet. All bacterial cells stain blue with this dye. Subsequently these cells are treated with Lugol's iodine solution (Iodine in potassium iodide solution) and washed with alcohol. At this stage if the bacteria retain the purple colour, they are described as Gram positive bacteria and if they lose their purple colour, they are described as Gram negative bacteria. The Gram negative bacteria can be subsequently stained with saffranine for further investigations. The Gram positive and Gram negative bacteria show certain morphological and physiological differences between them.
Gram Staining • A Gram stain of mixed Staphylococcus aureus (Gram positive cocci) and Escherichia coli(Gram negative bacilli), the most common Gram stain reference bacteria