What are bacteria?
Bacteria are very different from viruses. First of all, bacteria are much larger in size. The largest virus is only as big as the very smallest bacterium (singular for bacteria). But bacteria are still microscopic and cannot be seen with the naked eye. They are so small that the sizes of bacteria are measured in micrometers (10,000 micrometers = 1 centimeter). By comparison, the head of a pin is about 1000 micrometers wide. Though more complex than a virus, the structure of a bacterium is still relatively simple.
Structure: Most bacteria have an outer, rigid cell wall. This provides shape and support. Lining the inside of the cell wall is a plasma membrane. This is like the membrane found around all living cells that provides both a boundary for the contents of the cell and a barrier to substances entering and leaving. The content inside the cell is called “”cytoplasm.”” Suspended in the cytoplasm are ribosomes (for protein synthesis), the nucleoid (concentrated genetic material), and plasmids (small, circular pieces of DNA, some of which carry genes that control resistance to various drugs). All living cells have ribosomes, but those of bacteria are smaller than those found in any other cell. Some antibacterial medicines have been made that attack the ribosomes of a bacterium, leaving it unable to produce proteins, and therefore killing it. Because the ribosomes are different, the cells of the host are left unharmed by the antibiotic. Other antibiotics target certain portions of the cell wall. Some bacteria have long, whip-like structures called “”flagella”” that they use for movement.
Bacteria can occur in three basic shapes:
Name Basic Shape Example
(starting to divide)
Reproduction: Bacteria undergo a type of asexual reproduction known as “”binary fission.”” This simply means they divide in two, and each new bacterium is a clone of the original – they each contain a copy of the same DNA. Bacteria can reproduce very quickly. In fact, in an ideal laboratory situation, an entire population of bacteria can double in only twenty minutes. At this enormous growth rate, one bacterium could become a BILLION (1,000,000,000) bacteria in just 10 hours! Luckily, there are neither enough nutrients nor space available to support this rapid growth, or the world would be overrun with bacteria. As it is, bacteria can be found living on almost any surface and in almost any climate in the world.
Hosts and resistance: As stated, bacteria can grow nearly everywhere. These microbes have been around for billions of years because they are able to adapt to the ever-changing environment. They can find a home anywhere, and some of them live in places where it was once thought ‘nothing’ could survive. There are bacteria in the soil, at the depths of the ocean, living in the mouth of volcanoes, on the surfaces of teeth, and in the digestive tracts of humans and animals. They are everywhere and are very numerous. For example, a single teaspoon of soil is said to contain at least 1,000,000,000 bacteria. Most often, bacteria are thought of as a bad thing, but most bacteria are not pathogenic (disease-causing). In fact, many bacteria are very helpful to us. There are species that decompose trash, clean up oil spills, and even produce medicines. The few species that are pathogenic, however, give the rest of the bacteria a bad name.
Pathogens are rated on two characteristics – invasiveness and toxigenicity. Invasiveness is a measure of the bacterium’s ability to grow inside the host, and toxigenicity measures the capacity of the bacterium to produce toxins (chemical substances that cause damage to the host). The combination of these two characteristics gives the final rating of the bacteria’s virulence (ability to cause disease). A species does not necessarily need to have both high invasiveness and high toxigenicity to be rated highly virulent. One or the other can be high enough to cause the bacterium to be very virulent. For example, the bacterium Streptococcus pneumoniae (causes pnuemonia) does not produce a toxin, but it is so highly invasive that it causes the lungs to fill up with fluid from the immune response. In contrast, the bacteria Clostridium tetani (causes tetanus) is not very invasive, but it produces a potent toxin that causes damage at a very small concentration.
How does the body fight off a bacterial infection? Again, the body mounts an immune response to the foreign invader, producing antibodies for immediate help and future protection. Since this process takes about a week, antibiotics are usually employed in the meantime. Antibiotic drugs are usually only successful in treating bacterial infections, not viral, or fungal infections. Professionals are becoming concerned that the overuse of antibiotics when they are not needed may lead to the mutation of normal bacteria into antibiotic-resistant bacteria. Bacteria are very resilient and have already developed resistance to many antibiotics. Another concern is that the helpful bacteria that live in the digestive tract may also fall prey to the antibiotics. These bacteria, known as “”natural flora,”” produce vitamins that the host organism uses and needs, as well as help in the digestion of food.
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