Microorganisms That Cause Disease (1960)

[Music] when you think of a hospital and the treatment of disease you may think of x-rays and diagnosis or of the drama of surgery [Music] but if you should be suffering from an infectious disease the nature of your illness will be determined in the hospital laboratory where microscopes and other special tools are used to identify the tiny microorganisms that cause infectious diseases microorganisms that are capable of causing diseases are called pathogenic microorganisms these microorganisms cause pneumonia all microorganisms are either simple living plants such as these fungi or simple living animals such as these protozoa pathogenic microorganisms are found among each of the five kinds of microorganisms fungi bacteria viruses rickettsia and protozoa some invade the circulatory system and produce toxins that poison the body some cause disease by invading the lymph system almost all pathogenic microorganisms are parasites and live in healthy tissue and organs thus destroying them so cell destruction is the ultimate effect of all pathogenic microorganisms here we see some single-celled fungi all fungi are plants that do not make their own food they are dependent upon other organisms living or dead for their existence this is one example of what happens when pathogenic fungi invade the human body we can see the results of cell destruction we know this infectious disease as athlete's foot a rather common fungus disease this is the way the fungus looks under the microscope it is the pathogenic bacteria that cause many of our serious infectious diseases bacteria are found literally everywhere they are in our mouths and occasionally in other body tissue these bacteria normally in our mouths are frequently pathogenic and cause disease by destroying cells although scientists do not yet fully understand exactly how pathogenic bacteria destroy cells they do know a great deal about bacteria for example a single bacterial cell is simply a massive protoplasm surrounded by a firm cell wall bacteria secrete enzymes that enable them to digest food it is believed that such enzyme action is a significant part of the mechanism of cell destruction let's see some examples of how pathogenic bacteria destroy healthy cells this tube contains human blood the red color of the blood is caused by the presence of red blood cells this bottle contains a toxin toxins are poisons produced by pathogenic microorganisms this toxin is produced by the streptococcus microorganism this is a microscopic view of streptococcus when the streptococcal toxin is introduced into the blood we will see the destruction of the red blood cells in a short time the opaque suspension gradually becomes clear as the toxin destroys the red cells and they disappear this is one example of cell destruction by pathogenic microorganisms on this rabbit we shall see another kind of cell destruction we have shaved some of the hair from the rabbits back this has been done so that we may inject some pathogenic bacteria under the rabbit's skin over a period of three or four days we can see that a sore is developing on the skin this kind of cell destruction occurs when pathogenic bacteria invade certain body tissues viruses are another kind of pathogenic microorganism that cause cell destruction the virus you see here causes influenza like almost all viruses it can only be seen through an electron microscope which is capable of magnifying microorganisms more than one hundred thousand times viruses differ from other microorganisms in that they have no independent metabolism that is they grow only within tissue cells most viruses are very small these polio viruses are about the size of a very large molecule viruses occur as individual living particles as we see here and some may form crystals like this crystal of polio virus but even so within this crystal there is an orderly arrangement of virus particles let's see the cell destruction caused by viruses this is a cross-section of a normal spinal cord notice the large nerve cells after infection by polio virus most of the large nerve cells have been destroyed in the laboratory we can see the effect of another kind of virus pneumonitis virus this virus affects lung tissue we can infect this mouse by placing several drops of a solution containing the virus in the mouse's nose here we see the healthy pink color of a normal mouse lung before the virus has caused an infection but after the virus invades the lung producing pneumonia the lung becomes swollen and discolored let's see one more example of how pathogenic viruses destroy cells these test tubes contain cultures of living human cells we infect the cells with adenovirus the same virus that causes upper respiratory disease in humans in a series of micro views we can notice the progressive destruction of the tissue cells by the multiplying virus viruses have been used experimentally to cause cancers however the relationship between viruses and cancer is a problem that will require much more research research is also helping us to understand more about another group of pathogenic microorganisms the rickettsia rickettsia closely resemble the bacteria in structure as you can see in this electron micrograph like viruses rickettsia grow only in living cells rickettsia are transmitted by certain biting insects such as this tick we have seen the pathogenic fungi and bacteria which are single-celled plants and the smaller viruses and rickettsia which seem to be related now let's look at the protozoa this is an amoeba one of the many different kinds of protozoa protozoa are the simplest members of the animal kingdom protozoa have many different forms some have a means of locomotion some are pathogenic like this one this protozoan causes amoebic dysentery here is another pathogenic protozoan as seen in human blood this protozoan causes african sleeping sickness this diagram indicates how the protozoa which cause malaria destroy red blood cells when one of these protozoa enters a red blood cell as we see here it grows and starts to multiply within the cell within hours the cell is destroyed releasing more protozoa into the bloodstream where they may invade other red blood cells like all other pathogenic microorganisms protozoa do their greatest damage in those parts of the world where people live in crowded unsanitary conditions people who are totally unaware of pathogenic microorganisms often initiate mass epidemics through their ignorance even though scientists can now cure many diseases through their knowledge of how pathogenic microorganisms destroy cells there are still many questions to be answered for example just what is the mechanism that causes pathogenic bacteria to destroy cells and is there a relationship between viruses and the formation of cancers the never-ending search for the answers to these and many other questions continues through the sustained efforts of many scientists perhaps one of you may someday help to further our knowledge of microorganisms and infectious diseases you