NAME, ID #:_______________________________________________.
The human body is inhabited by a wide variety of microbes and parasites. Our bodies might be called the "Planet Human" because of these inhabitants. The population of organisms normally found on/in healthy humans is called the NATURAL or NORMAL FLORA. These organisms usually live harmlessly with us, causing little damage and in some cases they are actually beneficial and important to our survival. For example, the lactobacillus sp. that inhabit the vaginal region of the human female protects that tissue from infection by producing LACTIC ACID which maintains a LOW pH that is inhibitory to many potential pathogens. Any activity that effects the vaginal normal flora is likely to lead to infection. The human mouth is another region inhabited by strange and weird microbes. There are, of course the disreputable " bad breath microbes" that render us unacceptable in polite company. There are a host of other oral microbes that form plaques or that ugly film that coats our tongues at times. Among these plaque-producers lurk the "acid-producers" that produce acids which eat away our teeth, while providing a good living for dentists and toothpaste manufactures. While some of the normal flora of the mouth can contribute to health problems, they are harmless most of the time and prevent really dangerous pathogens from establishing themselves. For example, it is not uncommon that after a course of antibiotics some individuals get a painful yeast infection called THRUSH in the mouth. Apparently what happens is the antibiotics kill the normal floral and allow the yeast, which are probably always present in low numbers, to take over because its COMPETITION has been eliminated; the yeast not being affected by the bacterial antibiotics.
However, if a host's immune system becomes depressed or IMMUNE COMPROMISED, normal flora microbes can ESTABLISH LIFE-THREATENING INFECTIONS. Perhaps a more accurate way to view the situation is that we are inhabited by organisms that would happily CONSUME US if they could, but as long as we keep our DEFENSES up they present no serious problem. However, if we let our guard down they will devour us in a "NEW YORK MINUTE". For example, imagine how long the US would last if we destroyed all our weapons, disbanded our armed forces and declared that we wouldn't resist an invading force (this is exactly what happens in AIDS).
In the following three exercises you will isolate some NORMAL FLORA bacteria from your oral and nasal cavities and from your skin. The first bacteria you will attempt to isolate are Streptococcus sp. (streps). The Streptococcus and Enterococcus are G+, ELONGATED COCCI that tend to grow in LONG CHAINS. The Streptococcus are normal flora of the mouth, skin, intestine and upper respiratory tract while the Enterococci are usually found in the intestine and are associated with the feces; they are referred to as the FECAL STREPTOCOCCI. Many species are beneficial, being employed in cheese and pickle production, whereas others are SERIOUS PATHOGENS, including strains/species that produce pneumonia (click on 9-11), scarlet fever, strep throat, strep-blood poisoning (septicemia) and the "flesh-eating" disease. Streptococcus are aerotolerant in that they DON'T REQUIRE oxygen, but they tolerate it. They are catalase negative and usually grow best on rich medium. You will grow them on Blood Agar Plates (BAP). The streps are characterized by the effect they have upon red blood cells (RBC). Many streps produce enzymes that can lyse RBC, called HEMOLYSINS. Generally the more efficient a strep is at lysing RBC the MORE VIRULENT they are. Three major hemolysin types are commonly observed:
You will also use SELECTIVE MEDIA and DIFFERENTIAL MEDIA to characterize and isolate the desired bacteria. Selective media contains chemicals that either inhibit selected categories of microbes or strongly selects in favor of other categories, or some times it does both. A DIFFERENTIAL medium has something in it that shows a BIOCHEMICAL DIFFERENCE usually by coloring a colony or the area around it which indicates the presence of a particular enzyme(s). For example, you will be examining BAP plates for colonies with these types of hemolysis characteristics. BAP will grow a wide variety of bacteria, but it differentiates those that grow on the basis of their ability to lyse RBC. The Mitis-Salivarious medium is SELECTIVE as it contains potassium tellurite that inhibits enterics (like E. coli) and trypan blue and crystal violet that inhibit Staphylococcus. On-the-other-hand, Todd-Hewitt broth enriches the growth of pathogenic Streptococcus/Enterococcus while inhibiting other bacteria.
SAMPLE QUESTIONS: You should be able
to answer these questions at the conclusion of this laboratory. http://129.109.136.65/microbook/ch013.htm; Excellent information on the medical problems of streps.
Copyright © Dr. R. E. Hurlbert, 1999.
This material may be used for educational purposes only and may not be duplicated for
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