There are three main bacteria groups with respect to the potential health effects. So, they are as follows. The first group is called contaminants. These bacteria may be found anywhere in the environment. They usually live without doing any harm to humans. Micrococcus is an example of contaminant bacteria. The second group of bacteria is called opportunistic pathogens. They do not cause any disease unless the person is immunocompromised. It means that the person may be ill with some chronic illness, cancer, AIDS. Pseudomonas aeruginosa is an example of this group of bacteria. And the last group of bacteria is pathogenic bacteria. They may also be found in the environment but not so often as the representatives of the first two groups. These bacteria are not a part of the normal human flora and cause diseases. Vibrio cholerea, which causes cholera, is a representative of the group. Speaking about bacterias types, it is necessary to say that there are huge numbers of them. It is impossible to tell about all of them, so we'll describe only a small part of bacterias types. Acinetobacter is one of the bacterias types. It commonly occurs in the water, soil and sewage. Actinomycetes are filamentous bacteria that are usually found in soil. In most cases, it is thermophilic. These bacteria can cause respiratory problems in agricultural workers. Another type of all bacterias types is aerococcus found in soil, air, water, dust, plants, hospitals and meat products. This type is able to cause some kinds of diseases in lobsters, though they act as opportunistic pathogens to people. Aeromonas is usually found in fresh water, sewage and maybe pathogenic for reptiles and fish. With people, these bacteria are opportunistic pathogen that may lead to bacteremia and diarrhea. Agrobacterium usually occurs in the water and in soil, and sometimes in the intestinal tracts of animals. It can also cause opportunistic infections. Arthrobacter is found in soil. It causes secondary infection with immunocompromised patients. Bacillus can be present everywhere in the environment. These bacteria produce endospores that are able to make the bacteria resistant to the surrounding environment. In the form of the spores the bacteria can stay alive for years even in harsh environment. Some of the species are considered as pathogenic. Brevibacterium is non-pathogenic and is even used in the industry for cheese ripening. For this reason, they can be found on the skin and in the dairy products. Burkholderia was first detected as a plant pathogen. Nevertheless, now some of the species are used in agriculture in order to promote growth. This type can be pathogenic for people with cystic fibrosis, as well as for animals, for example horses. Citrobacter is usually found in feces of animals and humans. It can also be an opportunistic pathogen. Corynebacterium is isolated from skin and mucous membranes of the mammals. However, some of the species are parasitic and can be pathogenic for humans. Because of such a large number of bacterias types, it is sometimes rather difficult to make bacteria identification.