Microbes are single-cell organisms so tiny that millions can fit into the eye of a needle.
They are the oldest form of life on earth. Microbe fossils date back more than 3.5 billion years to a time when the Earth was covered with oceans that regularly reached the boiling point, hundreds of millions of years before dinosaurs roamed the earth.
Without microbes, we couldn’t eat or breathe.
Our Challenge: Determine the ways that viruses and bacteria are different.
Because bacteria and viruses cause many of the diseases we're familiar with, people often confuse these two microbes. But viruses are as different from bacteria as goldfish are from giraffes.
For one thing, they differ greatly in size. The biggest viruses are only as large as the tiniest bacteria.
Another difference is their structure. Bacteria are complex compared to viruses.
Bacteria
Many of us know bacteria only as “germs,” invisible creatures that can invade our bodies and make us sick.
Some microbes live on our skin and protect us from many harmful agents. The drier areas, like the back, have few microbes; moist areas, such as under the arm, have many more.
Few know that many bacteria not only coexist with us all the time, but help us do an amazing array of useful things like make vitamins, break down some garbage, and even maintain our atmosphere.
Bacillus represents a genus of Gram-positive bacteria which are ubiquitous in nature (soil, water, and airborne dust). Some species are natural flora in the human intestines. When grown on blood agar, Bacillus produces large, spreading, gray-white colonies with irregular margins. A unique characteristic of this bacterium is its ability to produce endospores when environmental conditions are stressful. The only other known spore-producing bacterium is Clostridium. Although most species of Bacillus are harmless saprophytes, two species are considered medically significant: B.anthracis and B. cereus.
Members of genus Clostridium are Gram-positive, spore-forming rods that are anaerobic. These motile bacteria are ubiquitous in nature and are especially fond of soil. Under the microscope, they appear as long drumsticks with a bulge located at their terminal ends. A Gram-stain is a good method for identifying Clostridium because the cell incorporates the dye while the spore remains unstained. Clostridium shows optimimum growth when plated on blood agar at human body temperatures. When the environment becomes stressed, however, the bacteria produce spores that tolerate the extreme conditions that the active bacteria cannot. In their active form, these bacteria secrete powerful exotoxins that are responsible for such diseases as tetanus, botulism, and gas gangrene. The four clinically important species of Clostridium will be discussed here: C. tetani, C. difficile, C. perfringens, and C. botulinum.
Our Challenge: Name at least three places microbes live. Can you think of any places that microbes might not live?
Microbiologists have found microbes living just about everywhere: in the soil, water and air; in animals, plants, rocks and even us!
The Streptococcus genus consists of Gram-positive, aerobic bacteria which appear as chains under microscopic observation. The organisms in this genus are characterized by a coccus appearance, a thick cell wall, and aerobic action on glucose. Four different classification systems exist for this important microorganism:
CLINICAL
As previously mentioned, Gram-positive bacteria are characterized by their blue-violet color reaction in the Gram-staining procedure . The blue-violet color reaction is caused by crystal-violet, the primary Gram-stain dye, complexing with the iodine mordant. When the decolorizer is applied, a slow dehydration of the crystal-violet/iodine complex is observed due to the closing of pores running through the cell wall. Because the crystal-violet is still present in the cell, the counter stain is not incorporated, thus maintaining the cell's blue-violet color. If you recall, most cell walls contain peptidoglycan, a molecule made of amino acids and sugar. A distinguishing factor among Gram-positive bacteria is that roughly 90% of their cell wall is comprised of peptidoglycan and a Gram-positve bacteria can have more than 20 layers of peptidoglycan stacked together to form the cell wall. That's pretty thick! Examples of common Gram-positive cells are Staphylococcus aureus and Streptococcus cremoris, a bacterium used in dairy production.
The Gram-positive cocci are grouped together based on their Gram-stain reaction, thick cell wall composition, and spherical shape. Most of the organisms in these groups are members of the Micrococcaceae family All of the organisms in these groups are non-endospore forming chemosynthetic heterotrophs. We will discuss only the clinically relevent bacteria from Micrococcus and Staphylococcus of the Micrococcaceae family. Streptococcus and Enterococcus(formerly a species of Streptococcus) are discussed as well because of the many diseases they inflict on humans. The chart below shows the paths to identification of the genera discussed.
Microcoocus is a Gram-positive, aerobic bacterium which is a member of the Micrococcaceae family. Micrococcus cells can be observed under the microscope as spherical cells forming pairs or clusters. If cultured in broth or on nutrient agar, the colonies may be red or yellow when observed unstained. Although these bacteria are a common human skin contaminant, they are relatively harmless to humans because they maintain a saprophytic lifestyle. They can also be found in freshwater environments or in soil. Three common species of Micrococcus are M. luteus, M. roseus, and M. varians.
