Can you help me with my biologie project?

Question

I need to find informations on useful bacterias (non pathogenic and that helps the human body) and harmul bacterias (pathogenic and that provokes illnesses).

Thanks in advance.

Answer 1

Non-Pathogenic Bacteria Block Inflammatory Response Pathway In Intestinal Tract
Science Daily — A team of Emory University pathologists has discovered that non-pathogenic bacteria within the gastrointestinal tract may be responsible for blocking an immune pathway that otherwise could cause an unhealthy inflammatory response to the millions of bacteria normally present in the intestine. A breakdown in this mechanism for bacterial tolerance could play a fundamental role in the pathogenesis of inflammatory bowel disease (Crohn's disease and ulcerative colitis) and other infectious intestinal diseases. The research was reported in the September 1 issue of the journal Science.

The gastrointestinal tract of humans and other vertebrates is home to a delicate bacterial balancing act in which a diverse ecosystem of non-pathogenic bacteria co-exist among potential pathogens, all under the watchful guard of protective immune cells. Although the intestinal non-pathogenic bacteria, or normal flora, are known to play a biological role in enabling the breakdown of certain vitamins and other substances, scientists have generally believed these bacteria to be otherwise inert residents of the GI tract. The usually harmonious co-existence between intestinal organisms and immune cells dates back through millions of years of evolution, from the time of the earliest known vertebrates.

The Emory team of pathologists, including Andrew Neish, M.D., James Madara, M.D. and Andrew Gewirtz, Ph.D., and their colleagues, discovered that non-pathogenic bacteria in the G.I. tract are not merely the innocent intestinal wallflowers they were presumed to be, but that they actually deliver a signal that blocks an important immune-system pathway called NF-KB -- a transcription factor involved in activating genes in the immune system.

"It's fascinating that the epithelium (lining of the intestine) can tolerate the presence of this density of bacteria while also being quite permeable to nutrients and fluids," says Dr. Neish. "Almost all other tissue types in the body are exquisitely sensitive to bacteria and their products. Now we have found a mechanism by which non-pathogenic bacteria block the inflammatory pathway and prevent cells in the G.I tract from responding as any other cell would respond. This mechanism for tolerance also could be fundamental to the pathogenesis of inflammatory bowel disease (Crohn's disease and ulcerative colitis) and to other infectious intestinal diseases," he said.

Crohn's disease and ulcerative colitis are diseases in which individuals develop a chronic and debilitating intestinal inflammatory response. Inflammatory bowel disease is one of the last few major unexplained diseases, although scientists have long suspected that it is related to lack of tolerance to the community of intestinal organisms. There is a possibility that the balance of beneficial to non-beneficial bacteria is altered in these patients," explains Dr. Neish. "A genetic flaw in the epithelial lining of the G.I. tract could also cause an abnormal response to the non-pathogenic bacteria."

The discovery also may shed light on the growing field of probiotics, in which investigators are experimenting with various species of benign bacteria that can be ingested with foods, such as lacto-bacillus (found in yogurt), to improve the intestinal health of patients with inflammatory bowel disease. The Emory research could elucidate a potential mechanism for the positive effects of probiotics.

"It's interesting that the organisms we are studying are non-pathogenic and have no ability to elicit inflammation themselves, yet they are able to block inflammatory pathways and create tolerance for themselves and perhaps other organisms," said Dr. Neish. "It turns out that some non-pathogenic bacteria have a significant reciprocal ecological interaction with the host. The host can mount an immune response to control resident bacteria, but even non-pathogenic bacteria have an ability to influence that immune response."

Pathogenic bacteria

Bacteria that cause disease are called pathogenic bacteria. Bacteria can cause diseases in humans, in other animals, and also in plants. Some bacteria can only make one particular host ill; others cause trouble in a number of hosts, depending on the host specificity of the bacteria. The diseases caused by bacteria are almost as diverse as the bugs themselves and include food poisoning (Source: Public Health Dept. Vic, Au), tooth ache (Source: Cosmetic Dentistry), anthrax (Source: Nebraska Health & human Services System), even certain forms of cancer. It is impossible to sum up all bacterial diseases and it would be pretty boring. The Infectious Diseases fact sheets (Source: New York State Department of Health) gives clear descriptions of infectious diseases, including viral diseases and some infections caused by other organisms. Some diseases are named after the organisms that cause them, or is it the other way round?

If you want to have a look at pathogenic bacteria under the microscope:

View here pathogenic bacteria under the microscope (Source: Des Moines Area Community College) which also describes their properties, as part of a course on medical microbiology. Some of the terms used here are explained in our exhibit on pathogenicity.
More links to microscopic pictures can be found in the exhibit on Images of bacteria.
Some pathogenic bacteria have received disproportionate attention in the press, e.g. the 'flesh-eating bacteria' (Source: Topix.net) , which in real life are called Streptococci. Indeed they can cause spectacular, but fortunately uncommon symptoms. In the press, pathogenic bacteria are sometimes represented as (deadly) dangerous enemies that lurk in the dark, unseen, ready to attack you. Although that is exaggerated some bacteria can be life treatening, for example Legionella pneumoniae, the causative of Legionnaire's disease. These bacteria survive in moist places like air conditioners or hot-water pipes. Though potentially life treatening, bacterial infections do not kill all their victims. If they did, and if they spread fast, they would eradicate their hosts completely. Although a popular theme for thrillers, this is a 'mission impossible' in real life. Some bacteria kill a high percentage of people infected (they have a so-called a high mortality rate), but their relatively inefficient rate of spreading makes up for that.

When an infectious disease spreads around an area, and the cases of new infections reach a certain number, we call it an epidemic. Read about epidemics (Source: American Natl History Museum) or visit the Epidemics Home Site (National Library of Medicine). If, on the other hand, a certain disease is always present in low numbers of cases in a given area, that disease is said to be endemic in that area. Some epidemics become wide-spread and quickly reach distant parts of the world: in modern times people travel fast and frequent, and our bacteria travel with us. A classical example of such a pandemic (in this case caused by a virus) was a new type of influenza ("Spanish 'flu") that reached continent after continent early this century, killing thousands of people on it's way. Although only a small proportion of the infected people died (the virus had a low mortality) so many people got infected that even the small proportion of deaths amounted to large numbers. An epidemic or pandemic can only occur if the population is not immune to that disease. Read our special feature file on the history of infectious diseases about the times that pathogens could spread unlimited. Our exhibit on our immune system explains how immunity can prevent disease. So why do epidemics occur? Either because they are caused by diseases that did not exist before, like AIDS, caused by the HIV virus, or because new variants of bacteria (or viruses) arrive in an area where they were not endemic before. This is why epidemics of the common 'flu' occur frequently: the virus causing influenza is able to change itself sufficiently to bypass our immunity built up from prior infections. Although not caused by bacteria, this site on influenza is very interesting if you want to understand epidemics of infectious diseases (Source: Ultranet EJ Kimball). Whenever a new virus type arises, there is the potential for a new epidemic. Fortunately, most of these new types are not as vicious as the Spanish 'flu.

An example of a bacterial disease that caused successive epidemics, and even pandemics, in recent times is Vibrio cholerae, the cause of cholera. Epidemiology is the study to establish the cause of a disease.

Read this classic of cholera in London in the last century: an epidemiological 'whodunit' with John Snow as the chief inspector (Source: Ultranet EJ Kimball).
Another classic epidemic in history was small pox raging through Europe in the 14th Century. Read our special feature file on the Black Death.
Bacteria have invented many different strategies to make us ill. These strategies, called bacterial pathogenicity, are the subject of an important division of medical microbiology. Understanding how certain bacteria make us ill can result in better treatment, vaccination, or prevention of that infectious disease. An example of such research is how treatment of ear infections can be improved (Source: Montana State Uni). In another exhibit some of the common mechanisms of bacterial pathogenicity are explained. In order to keep this information balanced, now that you know what pathogenic bacteria are, why not also check out how commensal bacteria are good for you.


The content of this page is copyright of the Virtual Museum of Bacteria and was written by Dr. T. M. Wassenaar (curator), with support of the Foundation for Bacteriology.

Answer 2

try these: lactobacillus for helpful
and Neisseria, Salmonella and Clostridia for harmful bacteria
many medical schools have websites that will help you understand these organisms