PATHOGENIC BACTERIA
Pathogenic bacteria are bacteria that cause bacterial infection. This
article deals with human pathogenic bacteria.
Although the vast majority of bacteria are harmless or beneficial,
quite a few bacteria are pathogenic. One of the bacterial diseases with
highest disease burden is tuberculosis, caused by the bacterium
Mycobacterium tuberculosis, which kills about 2 million people a year,
mostly in sub-Saharan Africa. Pathogenic bacteria contribute to other
globally important diseases, such as pneumonia, which can be caused by
bacteria such as Streptococcus and Pseudomonas, and foodborne
illnesses, which can be caused by bacteria such as Shigella,
Campylobacter and Salmonella. Pathogenic bacteria also cause infections
such as tetanus, typhoid fever, diphtheria, syphilis and leprosy.
Koch's postulates are criteria designed to establish a causal
relationship between a causative microbe and a disease.
Diseases
Each pathogenic species has a characteristic spectrum of interactions with its human hosts.Conditionally pathogenic
Conditionally pathogenic bacteria are only pathogenic under certain conditions, such as a wound that allows for entry into the blood, or a decrease in immune function.For example, Staphylococcus or Streptococcus are also part of the normal human flora and usually exist on the skin or in the nose without causing disease, but can potentially cause skin infections, pneumonia, meningitis and even overwhelming sepsis, a systemic inflammatory response producing shock, massive vasodilation and death.
Some species of bacteria, such as Pseudomonas aeruginosa, Burkholderia cenocepacia, and Mycobacterium avium, are opportunistic pathogens and cause disease mainly in people suffering from immunosuppression or cystic fibrosis.
Intracellular
Other organisms invariably cause disease in humans, such as obligate intracellular parasites that are able to grow and reproduce only within the cells of other organisms. Still, infections with intracellular bacteria may be asymptomatic, such as during the incubation period. An example of intracellular bacteria is Rickettsia. One species of Rickettsia causes typhus, while another causes Rocky Mountain spotted fever.Chlamydia, another phylum of obligate intracellular parasites, contains species that can cause pneumonia, or urinary tract infection and may be involved in coronary heart disease.
Mycobacterium and Brucella can exist intracellularly, though they are facultative (not obligate intracellular parasites.)For more information view the source:Wikipedia