Clostridium

Gram positive anaerobic, spore forming bacilli. Spores are refractile, oval or spherical and usually wider than the parent cell. They may be terminal, subterminal or central within the cell. Most clostridia possess flagella and motile but C. perfringens not. In 48 hour cultures, many of the bacilli may be Gram negative.

Clostridia lack the cytochromes required for electron transport to oxygen. They contain flavoprotein enzymes that reduce oxygen to H₂O₂ and to superoxide, and they lack the catalase, peroxidases and superoxide dismutase that destroy these toxic products. Therefore, they can grow only under anaerobic conditions. Some are found in animal, human intestines. Many species are pathogenic, but most saprophytes found in soil and water decomposing plant and animal matter. Some are of industrial importance for the production of chemical such as acetone and butanol. They are highly pleomorphic, rod shaped, motile. They are obligate anaerobes. The optimum temperature is 37⁰C, pH 7-7.4, growth relatively slow. The characteristic media is Robertson’s cooked meat broth- contains unsaturated fatty acids which take up oxygen. Clostridia can produce disease only when the conditions are appropriate.

Vibrios

            Gram negative, rigid, curved rods, actively motile by polar flagellum, nonsporing, noncapsulated, present  in  marine  environments  and  surface  waters. The most  important  member  of  the  genus  is    V. cholerae, the causative agent of cholera / Asiatic cholera. It was first isolated by Robert Koch.

Rickketsia

General characters

·         They are small Gram negative bacilli adapted to obligate intracellular parasitism, transmitted by arthropod vectors. They are primary parasites of arthropods such as lice, fleas, ticks, in which they are found in the alimentary canal. In vertebrates they infect vascular endothelium, reticuloendothelial cells.

·         This pleomorphic coccobacilli are nonmotile, noncapsulated. They stain bluish purple with Giemsa stain. It has a 3 layered cell wal  , a trilaminar plasma membrane and an outer slime layer.

·         Growth occurs in the cytoplasm of infected cells, nucleus etc. the optimum temperature is 32-35⁰C. they are readily cultivated in the yolksac of chick embryos, HeLa cells etc., in arthropods.

·         They multiply by binary fission.

·         They are inactivated by physical and chemical agents. They are rapidly destroyed at room temperature when seperated from host components, susceptible to tetracycline, chloramphenicol, ciprofloxacin, lysozyme. Sulfonamides enhance the growth and worsen the condition of patients.

·         They possess both RNA and DNA.

·         They are large enough to be seen under the light microscope and are held back by bacterial filters.