While thriving in a host or on an artificial culture medium, some bacteria produce substances that exert injurious effects in the host:
These are called ‘toxins’. In addition certain enzymes may be harmful to the host. Some bacteria produce pigments.
1. Bacterial toxins:
These injurious products of bacteria are of two types, (a) exotoxins (extra-cellular) and (b) endotoxins (intracellular). Toxins diffuse readily from the living bacteria into the surrounding medium. They can be obtained from the medium after removal of the bacteria. This can be done by centrifugation or by filtering through a Seitz filter.
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The toxins remain in the supernatant fluid in the case of centrifugation and in the filtrate in the case of filtration. Certain gram positive bacteria secrete exotoxins, for example, Corynebacterium diphtheriae. Exotoxins are antigenic and are rapidly destroyed by heat.
2. Endotoxins:
These are toxins intimately associated with the cell wall of most gram negative bacteria. They are released after death and disintegration of the bacteria. The majority of pathogenic bacteria produce endotoxins only. As mentioned in the previous paragraph for exotoxins-the endotoxins would be present in the residues and not in the supernatant (centrifugation) or in the filtrate (filtration).
3. Bacterial enzymes:
(a) Proteolytic enzymes. An enzyme responsible for decomposition of dead animal and vegetable matter in nature.
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(b) Coagulase. This is often demonstrated during the study of biochemical properties of some pathogenic bacteria.
(c) Amylase. This enzyme is capable of splitting, starch and is not much used in the study of bacteria.
(d) Lactic acid fermentation.
(e) Alcoholic fermentation. Bacterial pigments
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Many bacteria have the capacity to produce pigments, e.g. Staphylococcus aureus-go\den yellow pigment and Pseudomonas pyocyaneus-green pigment. Certain pigments are restricted to the bacterial colonies while others can diffuse to the surrounding medium.