Prevention and control of bacterial disease

Although bacteria were first seen and depicted with remarkable accuracy by Anthony van Leeuwenhoek in the late 17-th century, they were not generally recognized as a cause of disease until 100 years ago. Recognition of microbes as disease agents led directly and swiftly to control measures. Among them were: physicians, surgeons, nurses, and hospitals. Some organisms make chemicals that prevent the growth of bacteria. These chemicals are called antibiotics. The first antibiotics where discovered in 1929 by Alexander Fleming. They are used to kill pathogenic bacteria. Bacteria, produce most antibiotics; fungi, especially the actinomycetes, form few. These antibacterial agents act by interfering with metabolic reactions essential to the bacteria but not to the cells. Penicillin, for example, inhibits bacterial growth by interfering with the cross-linking of the peptide chains in the bacterial cell walls.

The battlefields of World War II were the proving grounds for new antimicrobial drugs, such as sulfa and penicillin. Penicillin is a well-known antibiotic that cures strep throat and other diseases by killing the bacteria, which cause it. Penicillin was the first discovered antibiotic – by definition, a chemical that is produced by a living organism and is capable of inhibiting the growth of microorganisms.

Immunization, which involves the stimulation of the body’s natural defenses against a disease-causing agent, is also responsible for the prevention of many bacterial diseases, including diphtheria, whooping cough and tetanus.

Table 3.1

3.3. Plantlike Protists. Kingdom Protista

Plantlike protists are grouped with protists because they are one-celled living things that have a nucleus. Some of the algae that are plantlike protists such as green algae, golden algae, euglenoids and fire like algae.

3.3.1. Phylum Clorophyta

Green algae that are plantlike protists grow in different ways; some of them grow as a single cell. Others grow side by side and form a chain. Spirogyra is a kind of green algae that grows as a chain of cells. The cells do not work together as they would in a many-celled plant. So, each cell is a plantlike protist.

Other kinds of green algae grow as a group, or colony. The green algae that grow on tree bark often grow in a colony. Another kind, called volvox, grows in a colony that looks like a hollow, green ball.

Perhaps most important members of the golden algae are the diatoms. Diatoms are different from other kinds of algae in many ways. The cell wall of a diatom is a glasslike shell that is formed in 2 parts. The 2 parts fit together as do the lid and the bottom of a box. The shells have many beautiful shapes. In fact, some people call diatoms the “jewels” of the ocean. These shells can be used in making such things as toothpaste, dynamite, and metal polish.

The euglena is a member of Euglenophyta. Euglenas are a puzzle to scientists because they are like animal-like protists in some ways (they do not have a cell wall, can move easily from place to place, and can take in tiny pieces of food) and like plantlike protists in other ways (because they have chlorophyll and can use sunlight to make their own food, they are usually grouped with the plantlike protists).

Algae

Algae are present in all bodies of water. When conditions are favorable, algae multiply rapidly and form colored paths called blooms on the surface of the water.

These algae blooms pose a variety of problems. They are a threat to Aquatic plants and animals to certain industries that depend on marine life, and to supply of drinking water

Toxic ocean blooms, caused by algae Dinoflagellates called red tides.

Toxins concentrate in marine animals, such as clams and mussels and can cause a fatal form of paralytic shellfish poisoning. The spray of red tide dinoflagellates causes respiratory problems in human.

The blue-green algae are monerans. They are grouped with monerans because they are small, one-celled living things that do not have a nucleus. Other algae, such as the seaweed called kelp, are plants. They are grouped with plants because they are made up of many cells that work together. In other words, different cells of a kelp plant perform different jobs for tire plant.

Still other algae are plantlike protists.

Algae vary greatly in size and shape, from microscopic, hard-shelled forms to rubbery kelps that grow as long as 70 m. Like those of all protists, the cells of algae are eukaryotic. Most algal cells are supported by an inner wall of cellulose. Cells are held together by a jellylike substance called pectin.

Some algae are unicellular; others are multicellular. Many unicellular algae move by means of flagella. Kelps and many other multicellular algae are nonmotile. The bodies of multicellular algae consist of filaments that become meshed together into a solid mass. An unspecialized multicellular body is called a thallus.

Algae are common in freshwater lakes, streams, and the oceans. There they may form a layer of green scum on the water’s surface or hang in strands from rocks or logs. Along with protozoa and other small organisms, algae make up plankton. Plankton is the food source for most of the world’s water-dwelling organisms. Billions of tiny, drifting algae are called phytoplankton.

Algae also live on land in the thin films of water found on rocks and soil particles. Some species of algae thrive in snow – fields, deserts, cold springs, or the almost boiling water of hot springs. Air samples from 15000 m above sea level have contained algal cysts which are much like protozoan cysts.

Life on Earth involves a delicate balance between organisms that produce food and organisms that consume it. Among the organisms that produce food – the autotrophs – no group is more important than the algae. Algae are the autotrophic members of the kingdom Protista. They are considered as plant-like protists because they contain chlorophyll and carry out photosynthesis. Like marine and freshwater protozoa, algae provide food forcountless species of water-dwelling animals.