Classification

We have heard stories about people who got sick because of bacterial infection. But what is this organism that causes severe ailment when let untreated? Bacteria (sing., bacterium) are minute unicellular microorganisms, the smallest ones having all the necessary protoplasmic equipment for growth and self-multiplication at the expense of available foodstuffs. Bacteria can be observed and studied well using the microscope. They can start with rather simple substances and synthesize them into complicated organic moieties. They use food materials only in solution and excrete waste products in fluids that must diffuse outward. There is no special structure for intake of solids for digestion or for release of solid particles to the environment. In the early days of microbiology, it was believed that bacteria belonged to the animal kingdom, but then for a period of years, it seemed more suitable to classify them with plants.

Unlike plants, bacteria ordinarily do not contain chlorophyll and may be able to move about independently in their environment. Today we classify them as procaryotes. Bacteria are morphologically simpler than the cells of the higher organisms, and as is true for procaryotes, they lack an organized nucleus. Despite their relative simplicity, they have an elaborate and complicate life history.

Distribution

Bacteria are widely distributed in nature They have adapted to every conceivable habitat They are found within and upon our bodies and in the food we eat, the water we drink, and the air we breathe They are plentiful in the upper layers of the soil and no place on earth, except possibly the peaks of snow-capped mountains, is free of them. They are found in frozen Antarctica and in the hot water of the geysers in Yellowstone Park. They can be found in the stratosphere at a height of 20 kilometers (km.) and in ocean sediments at a depth of 11,000 meters (m.); they are able to grow from 5° to -2,° C, the temperature of 90% of the world’s oceans. Under the microscope, bacteria can be examined closely.

When scrutinized under the microscope, our skin has a large bacterial population, and bacteria make up a generous portion of the contents of these alimentary tract. There are several thousand species of bacteria; of this number, about 100 produce disease in humans. The ratio is given as 30,000 nondisease producing bacteria to 1 disease producer. Some of the bacteria that produce disease in humans also produce disease in the lower animals. Others produce disease in the lower animals only, and still others attack only plants. The majority, however, do not attack human beings, lower animals, or living plants and either do not affect animals and plants at all or are actually helpful to them. In fact, if the activities of bacteria were to cease, all plant and animal life would soon become extinct.

After close observation with the aid of the microscope, bacteria can be classified into pathogenic and nonpathogenic. Bacteria that cause disease are spoken of as pathogenic; those that do not cause disease are nonpathogenic.

Morphology

Shape

When viewed under the microscope, bacteria have three well known shapes. Coccus appears as spherical. Bacillus is a rod-shaped bacterium. Spiral shaped are vibrio, spirillum, or spirochete.

Variations exist with these three shapes. Under the microscope cocci are not necessarily perfectly round, but may be somewhat elongated, oval, or flattened on one side. Rod-shaped bacilli may be long and slender or short and plump. Short, thick, oval-shaped bacilli resembling cocci are known as coccobacilli. The ends of bacilli are usually rounded but may be square or concave. The three spiral-shaped bacteria are each distinct. The vibrio is a curved microbe shaped like a comma. The appearance of the other two when viewed under the microscope relates to their movements. In the spirillum, the long axis remains rigid when it is in motion, whereas in the spirochete, the long axis bends when it is in motion.

When bacteria, especially cocci, divide, the manner in which they do so and their tendency to cling together often give them a distinct arrangement. When viewed under the microscope, you will know the distinct appearance of the cocci. Cocci that divide so as to form pairs are known as diplococci. The opposing sides of diplococci may he flattened (examples, gonococci and meningococci). Cocci that divide and cling end to end to form chains are known as streptococci. Those that divide in an irregular manner to form grapelike clusters or broad sheets are known as staphylococci. Other patterns for cocci are in groups of four (tetrads) and cubic packets of eight (sarcinae). No pathogenic cocci are found in the latter group. Bacilli that occur in pairs are known diplobacilli and those that occur in chains as streptohacilli. The diplobacillus and streptobacillus arrangements are unusual. When some bacilli divide, they bend at the point of division to give two organisms arranged in the form of a V. This is known as snapping. In other cases they tend to arrange themselves side by side. This is known as slipping.