Relationship between normal flora and a host

Normal flora of human host: Types, Examples and Roles -

relationship between normal flora and a host

3 Learning outcomes: At the end of the lecture, students should be able to: describe the factors that effect and determine the normal flora. distinguish between. Normal microbiota are the microorganisms that reside in the bodies of all humans . Explain the relationship between the normal microbiota and the host upon. This report will focus on the relationships between microbes and humans. Normal flora can be found in many sites of the human body including the skin A positive host-microbe relationship is usually described as either.

Mutualism Commensalism Parasitism 5 Mutualism Both members of the association benefit. One classic mutualistic association is that of the the lactic acid bacteria that live on the vaginal epithelium of a woman. The bacteria are provided habitat with a constant temperature and supply of nutrients glycogen in exchange for the production of lactic acid, which protects the vagina from colonization and disease caused by yeast and other potentially harmful microbes.

Lactobacilli in association with a vaginal epithelial cell CDC 6 Commensalism One organism benefits but the other is neutral there is no harm or benefit. Staphylococcus epidermidis, a consistent inhabitant of the skin of humans. The bacterium produces lactic acid that protects the skin from colonization by harmful microbes that are less acid tolerant.

But it has been suggested that other metabolites that are produced by the bacteria are an important cause of body odors good or bad, depending on your personal point of view and possibly associated with certain skin cancers. A parasite that causes disease in its host is called a pathogen.

Some parasitic bacteria live as normal flora of humans while waiting for an opportunity to cause disease.

Normal flora of human host: Types, Examples and Roles

Other nonindigenous parasites generally always cause disease if they associate with a nonimmune host. The microorganisms that grow in or on the body without producing obvious harmful effects on the host makes up the normal flora. Symbiotic relationships with the host.

relationship between normal flora and a host

The normal flora is acquired at birth. Just as host-microbe relationships can be positive or neutral, they can also be negative. Such a host-microbe relationship is usually described as parasitic or pathogenic.

relationship between normal flora and a host

In a parasitic relationship the microbe benefits at the expense of the host and similarly in a pathogenic relationship the microbe causes damage to the host. In both cases the cost to the host can vary from slight to fatal.

relationship between normal flora and a host

And in most cases the relationship will actually remain positive. The host provides a niche and nutrition for the colonizing microbe and the microbe occupies a space that a potential parasite or pathogen might otherwise colonize.

relationship between normal flora and a host

In these cases microbial communities may even aid in digestion or synthesize nutrients for the host. However, life is not always perfect, and in certain situations good-standing members of your normal flora can cause disease or invading pathogens can displace them.

The result will be disease. Life on the Surface, the Skin Human skin is not a particularly rich place for microbes to live. The skin surface is relatively dry, slightly acidic and the primary source of nutrition is dead cells. This is an environment that prevents the growth of many microorganisms, but a few have adapted to life on our skin. Propionibacterium acnes is a Gram positive bacterium that inhabits the skin.

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. A Bacterial Sneeze, the Nose 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.

relationship between normal flora and a host

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. Braving Stomach Acid What kind of organism would live in a highly acidic pH environment like the stomach? One explanation for tissue tropism is that the host provides essential nutrients and growth factors for the bacterium, in addition to suitable oxygen, pH, and temperature for growth.

Lactobacillus acidophilus, informally known as "Doderlein's bacillus" colonizes the vagina because glycogen is produced which provides the bacteria with a source of sugar that they ferment to lactic acid.

Is yogurt good for your microbiota?

Specific adherence involves biochemical interactions between bacterial surface components ligands or adhesins and host cell molecular receptors. The bacterial components that provide adhesins are molecular parts of their capsules, fimbriae, or cell walls. The receptors on human cells or tissues are usually glycoprotein molecules located on the host cell or tissue surface.

Specific adherence involves complementary chemical interactions between the host cell or tissue surface and the bacterial surface. The adhesins of bacterial cells are chemical components of capsules, cell walls, pili or fimbriae.

The host receptors are usually glycoproteins located on the cell membrane or tissue surface.