Microorganisms: Harmful Activities (1958)

[Music] [Music] disease for many centuries the scourge of all mankind. But man has learned to protect himself by such means as isolating the sick, using heat to kill infectious organisms, vaccinating to immunize himself and his animals and breeding disease resistant plants. Also, he has learned to preserve his foods by such methods as refrigeration and canning. These practices are necessary to overcome the harmful effects of certain microorganisms that cause disease and spoilage of foods and other materials. When these microorganisms grow in a particular environment, they secrete such substances as enzymes or toxins which cause disease in living tissue and decomposition in foods and other materials. Our knowledge of such harmful activities of microorganisms is the result of the brilliant studies started by pastor and other scientists including Metchnikov Erlick and Kau the German bacteriologist who proposed certain postulates for proving that a specific disease is caused by a specific microorganism. Coox's postulates consist of four steps. First, observe the same organism in every case of the disease. Second, isolate the organism and grow as a pure culture. Third, inoculate the pure culture into a susceptible host to reproduce the disease. and fourth, reisolate the same organism from the experimentally diseased host. As an example of the application of these postulates, let us examine a group of tomato plants. Close observation reveals that an infection has developed on the stems. Microscopic examination of the infected tissue of many plants shows the same bacteria. To isolate the organism, the diseased tissue is removed and treated with a disinfectant to eliminate bacteria which may be present on the surface. After the tissue is washed with sterile water to remove the disinfectant, a sample is cut from the infected tissue and placed in a sterile mortar where it is ground to release the bacteria present. Some of the liquid containing the bacteria is stre over the surface of a material which permits these organisms to grow. After a period of incubation, areas of bacterial growth appear on the surface. The bacteria which have been isolated seem to be identical to those originally seen in the infected tissue. These organisms are now transferred to fresh nutrient material on which they grow as a pure culture, thus satisfying the second of CO's postulates. To fulfill the third postulate, a suspension of the bacteria is made and injected into a healthy tomato plant. After a period of time, an infection develops at the site of the inoculation. Upon reisolation, if the bacteria from the infected tissue are found to be the same as those in the original infection, they must be responsible for the disease. By application of Cox postulates, the specific organisms responsible for a variety of diseases have been discovered. Many of the organisms which cause disease infect only a specific host. Diseases of plants do not occur in man and other animals. As is true with plant diseases, animal diseases may occur in more than one species. In addition to affecting specific hosts, the organisms are often localized in certain tissues such as streptooxy which cause sore throat or tubacal basilli found in the lungs or polio virus which damages nerve cells. Normally the skin and mucous membrane provide effective barriers against the entrance of microorganisms. When these barriers are broken, what defenses does the body have to withstand infection? When disease- producing organisms enter the bloodstream, the body is stimulated to produce larger quantities of white blood cells called fagosytes. As seen through the microscope, these fagosites engulf the invading bacteria and destroy them. In addition to the action of white blood cells, these foreign organisms stimulate the body to produce chemical substances known as antibodies, which react with the organisms or their toxins. These antibodies may act by causing the bacteria to clump together, thus aiding the body to overcome the disease. These mechanisms are extremely important in immunity, the body's resistance to disease. There are various types of immunity. In a few instances at birth, a natural immunity may be present. But more frequently, protection is developed and is known as active immunity. This may be brought about by having a disease and recovering or by introducing into the body a vaccine or toxoid that stimulates the production of specific antibodies. Microorganisms are cultivated in different ways for preparation of the vaccines against the specific disease they cause. Some bacteria are grown in test tubes containing special food materials. Certain viruses are grown in eggs and other tissues or the microorganisms may be cultivated in large quantities. Finally, the organisms or their toxins are treated with heat or chemicals to ensure safe and effective preparations. Thus, vaccines and other biological products essential in preventing or combating many diseases are available for our use. When certain disease- producing organisms enter a body in which immunity is not adequate, antibodies from an immune individual are injected to give immediate aid or protection. In this instance, an antitoxin is used. The antitoxin is prepared commercially by injecting a horse with treated toxin called toxoid which stimulates the animal to produce antibodies. After a period of time, the blood of the horse contains the antibodies against the specific toxin which had been injected. The blood is processed and the resulting antitoxin is used as a protection against the possible harmful effects of the organisms. Such protection is an example of passive immunity. There is a distinct difference between passive and active immunity. In passive immunity, upon injection of the antibodies from another individual, a high level of immunity is immediately reached, but it lasts for only a short time. In active immunity, upon injection of the vaccine or toxoid, a gradual increase in immunity occurs. Subsequent injections cause a great increase and the immunity lasts a very long time. If the defenses of the body are inadequate or have been overcome, other means must be found to combat the infection. The sulfa drugs, various antibiotics and other preparations are then used in the treatment of the disease. The control of disease depends not only upon individual immunity but also upon effective community safeguards against the spread of disease in the purification of potentially polluted water. Filters of sand and gravel serve to remove bacteria and the disinfectant chlorine is added to ensure a safe water supply. In milk pasteurizers, heat is used to destroy disease producing bacteria. And heat is important in the sterilization of surgical instruments. Ultraviolet radiations and chemical antiseptics also serve as barriers to the possible spread of harmful microorganisms. Undesirable activities of microorganisms are not limited to disease. Spoilage of fresh and processed foods results in considerable economic loss. The organisms responsible are detected and are proved to cause the spoilage by a procedure similar to that developed by CO for identifying disease- producing microorganisms. Moreover, these spoilage organisms are controlled by methods similar to those used against disease-causing organisms. Heat permits preservation of food in sealed cans. Cold or freezing temperatures serve as another method of preserving foods and chemicals added to certain foods prevent spoilage. Microorganisms are also responsible for deterioration of other materials. They cause damage to a variety of fabrics and continual attention must be given to wood products which are exposed to the destructive effects of microorganisms. The rotting of wood is prevented or delayed by chemical treatments which inhibit the growth of microorganisms. Each outbreak of disease, each instance of food spoilage and destruction of property creates a challenging problem. Only through continual research using procedures initiated by pastor Caul and others can the microbiologist of today learn to control these harmful microorganisms. [Music] [Applause] [Music]