MadSci Network: Microbiology

Re: Whose mouth has more germs in it, mine or my dog's.

Date: Fri Feb 27 14:21:26 1998
Posted By: Amy Caudy, Undergraduate, Biology, Washington University
Area of science: Microbiology
ID: 886680357.Mi

It sounds like you are doing a science fair project in microbiology. I've always enjoyed microbiology, and began my science fair career with such a project.

You can swab your and your dog's mouths and spread the swabs on a nutrient agar plate. You will probably see differences in the amount of bacteria and fungi, as well as the types. You will want to record not only the number of things that grow on your nutrient agar plate, but what they look like. Both you and your dog have lots of bacteria and fungi (what you call "germs") on your bodies.

Safety is important in microbiology.

You're probably wondering how bacteria get there in the first place. I found this article, summarized below. The necessary information is there for you to get a copy.

TITLE: The Bugs Within Us



CITATION: September, 1992, 26: 37-39, 41-42.

YEAR: 1992

ABSTRACT: A microscopic zoo inhabits all those parts of the body that are exposed to the outside, including the skin and the entrances and exits to the respiratory tract, urinary tract, genitals, eyes, ears, and the entire length of the digestive tract. The bacteria, protozoa, viruses, and fungi that live within the body come in two basic varieties: residents and transients. The resident microbial flora are always present in their own niches, but transients come through various exposures and leave by bathing, sweating, urine, tears, and feces.

The body is first exposed to microbes during passage through the birth canal. Within 12 hr. following birth, several species are present in the intestinal tract, transferred from the mother, from food, and from the baby's first coming in contact with the mouth. These exposures are normally beneficial because they stimulate an infants own natural immunity. The normal flora of the human body also manufacture certain nutrients and occupy areas in the body that might otherwise become a breeding ground for pathogenic organisms.

Members of the resident flora generally do no harm because they are present in low numbers. But in some cases, as with the yeast Candida albicans which inhabits the vagina, bowel, mouth, and skin, a significant increase in the microbial population can cause trouble in the form of a vaginal yeast infection or thrush in the mouth. Changes in the chemistry of the microbe's habitat are generally the cause of such population explosions. The physical barriers which prevent resident microbes from gaining access to the inner body cavities and the blood where they might be able to cause disease are considered the first line of defense against disease. In those cases where microbes do enter unfamiliar body areas, they are generally destroyed by the second line of defense, the immune system.

In a more subtle way the normal microbes in the body can also usher in infection when their numbers fall. Changes in microbial habitats which result in reducing resident microbial populations may favor the growth of pathogenic bacteria. Drastic changes in diet or taking antibiotics may cause such changes in the intestinal microflora and result in diarrhea. Douching decreases the natural bacterial population in the vagina and increases alkalinity which can favor the growth of yeast. Because many health problems seem to result from lowered levels of lactobacilli, the consumption of foods cultured with lactobacilli, such as yogurt, has been recommended.

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