How can normal flora cause disease

In some experiments, germ-free animals can be infected by 10 Salmonella bacteria, while the infectious dose for conventional animals is near 10 6 cells. The normal flora may antagonize other bacteria through the production of substances which inhibit or kill nonindigenous species. The intestinal bacteria produce a variety of substances ranging from relatively nonspecific fatty acids and peroxides to highly specific bacteriocins, which inhibit or kill other bacteria.

The normal flora stimulate the development of certain tissues , i. The caecum of germ-free animals is enlarged, thin-walled, and fluid-filled, compared to that organ in conventional animals. Also, based on the ability to undergo immunological stimulation, the intestinal lymphatic tissues of germ-free animals are poorly-developed compared to conventional animals.

The normal flora stimulate the production of natural antibodies. Since the normal flora behave as antigens in an animal, they induce an immunological response, in particular, an antibody-mediated immune AMI response. Low levels of antibodies produced against components of the normal flora are known to cross react with certain related pathogens, and thereby prevent infection or invasion. As the name implies P. Although acne outbreaks can result in emotional and physical discomfort the infection is not life threatening.

A point complemented by P. Another prominent member of the skin flora is Staphylococcus epidermidis. This is a highly adapted Gram positive bacterium that can survive at many sites throughout the body. In such cases, S.

Under this scenario S. Today, researchers and manufacturers are developing new approaches to designing catheters that prevent biofilm formation. The human nose is home to the infamous Gram positive bacterium Staphylococcus aureus , best known for its role in hospitals where it is a major cause of surgical wound and systemic infection.

You may have heard of S. Infections of this bacterium are now a very serious threat to human health because it has become resistant to all commercially available antibiotics, including methicillin and vancomycin. It is often carried in the noses of health care workers and transmitted from patient to patient. Why some people carry S. A predominant member of this community is the Gram positive bacterium Streptococcus mutans. It grows on biofilms on the surface of teeth plaque where it consumes sugar and converts it to lactic acid.

Lactic acid erodes the enamel on the surface of teeth, which leads to the formation of cavities. Interestingly, a group of researchers have developed a strategy to combat dental decay by using a genetically modified strain of bacteria that produces a toxin that specifically kills S. The trick is that this genetically modified strain of bacteria will only survive in your mouth if you provide it with specific nutrients.

Basically, you brush the new strain of bacteria onto your teeth and they produce a toxin that prevents the growth of S.

To maintain the strain of bacteria in your mouth you provide the essential nutrient by swishing daily with a mouthwash—just remember to feed your bacteria!

Whether or not tooth decay is a disease serious enough to warrant the use of a new strain of genetically modified bacteria is debatable. The effects of altering the populations of bacteria in the mouth may have unpredictable consequences. For example, Streptococcus pneumoniae is a much more threatening bacteria that can colonize the mouth. Under normal circumstances the growth of S. Would the removal of S. What kind of organism would live in a highly acidic pH environment like the stomach?

One organism that has been discovered living in the human stomach is the Gram negative bacterium called Helicobacter pylori [4]. How can it survive? Well, it creates a less acidic microenvironment. In addition, H. Figure 2: H. Within the lining, the microbe is then able to avoid pH levels that would normally kill it. Here, it may also produce ulcers. Exactly how H. It is thought that the bacterium may induce an immune response in the host that results in uncontrolled local inflammation and the generation of ulcers.

Furthermore, it is now clear that gastric cancer is associated with H. Research is underway to determine what role H. We are learning more and more about the benefits of bacteria. Certainly, with the help of fungi, bacteria play a vital role in breaking down and recycling dead organisms. Healthy internal tissues e. These bacteria that are regularly found at a given site are referred to as "normal flora. Their makeup depends on age, sex, stress, nutrition, etc.

The table below shows a partial list of some of the more common bacteria regularly found in and on humans.

The number of plus signs indicates their relative abundance. Some data suggests that inappropriate use of antibiotics and the avoidance of microbes through disinfecting ourselves and our environment may have adverse effects on health. Microorganisms are present everywhere. Despite their overwhelming abundance, relatively few of the thousands of species Merck and Co. From developing new therapies that treat and prevent disease to helping people in need, we are committed to improving health and well-being around the world.

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