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The Koch's postulates that are used for judging if a bacteria is the cause of the diseases and for identification of the disease-causing bacteria include:
- bacteria must be present in all cases of the disease
- bacteria must be isolated from the infected patient and grown in a culture
- the individual (i.e., experimental animal) can be infected with the pathogen if a pure culture is inoculated in a healthy organism
- the bacteria that was reisolated from the experimental organism must cause the same disease
Although the postulates cannot be applied to all pathogenic bacteria and viruses, some bacteria like tuberculosis fit these postulates. As a result, according to the results of the experiments, Koch successfully isolated tuberculosis bacteria from the infected individuals and incubated the microorganism in a culture. Healthy individuals did not contain the bacteria, while experimental animals could be infected using isolated and reisolated microbes. However, some organisms cannot be isolated in the culture (i.e., Mycobacterium leprae) and do not fulfil the pustulates.
Bacterial toxins can be distinguished by their nature and mechanism of action. Two main groups of bacteria toxins are:
- endotoxins that are the parts of bacteria (i.e., membrane). These toxins are thermostable, weak immunogen antigens, and are characterized by general toxicity and inflammation.
- exotoxins are proteins that are secreted by bacteria and have a cell- or tissue-specific toxic effect.
More specifically, toxins can induce the lysis of the host membrane, block synaptic neurotransmission, activate cellular adenylyl cyclase stimulating diarrhea, block protein synthesis, and inhibitors of cells adhesion.
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