Bacteria - Laboratory Study (1958)

[Music] in his quest for exploration generals opened before him through the used telescope he has made startling discoveries of great worlds beyond his own in a similar way he has used the microscope to discover the minut worlds that exist around him are these the world of microscopic living things has influenced the welfare of mankind significantly low magnification with the microscope reveals protozoa one celled microorganisms animal life in its most primitive form and algae microscopic green plants capable of food production by photosynthesis higher magnification is required to study yeast single-celled plants which while magnification approaching 1,000 times issues discuss of this microscopic world yet an electron microscope capable of magnifying many thousands of times reveals living things even smaller than bacteria these are viruses the smallest known forms of life although the microscope is useful in the study of bacteria to learn more about these microorganisms it is necessary to grow them in the laboratory this permits study of characteristics important in understanding the activities of bacteria in nature and in disease bacteria are grown on food materials containing the same elements as those required by larger living things if a solid medium is needed agar obtained from seaweed usually is added such a nutrient solution is called a culture medium to keep out unwanted organisms containers are covered with metal caps or are plugged with cotton then before use all nutrient materials are sterilized in an autoclave which uses compressed steam in a manner similar to a pressure cooker as the pressure within the autoclave increases the temperature also Rises until 121 degrees centigrade or 250 degrees Fahrenheit is reached and maintained for the necessary time at the end of the heating period the containers and their contents are now sterile free from all living organisms with these nutrients study of bacteria can now be made under controlled conditions for example to grow the bacteria present in soil a small sample of soil is mixed with sterile water and then some of the mixture is transferred into a sterile petri dish a special plate used for cultivating bacteria the lip of a tube containing growth material is heated in a flame then the contents are added carefully to the diluted soil sample and mix gently after the nutrient medium has cooled and hardened the dish is inverted and placed in an incubator which maintains a constant temperature to encourage growth of bacteria during incubation each bacterial cell in the soil sample grows and divides to form two new cells as shown by time-lapse photography through the microscope the division is repeated approximately each half hour this method of reproduction is known as fishin thus great numbers of cells are created in a short time after one or two days of incubation this tremendous mass of bacterial cells becomes visible to the unaided eye these visible masses are known as colonies each colony can arise from a single cell the development of colonies also can be seen when fingers normally carrying bacteria are rubbed across the surface of a nutrient material time-lapse photography reveals the development of colonies to examine the bacteria from the colony a drop of water is placed on a glass slide a wire transfer needle is sterilized in the flame of a burner to destroy bacteria which may be present after the needle has cooled a portion of a colony is picked up and transferred to the drop of water the needle should be sterilized in the flame after as well as before each use a cover glass is then placed over the preparation with the high power objective living bacteria from the selected colony become visible however to see them more clearly bacteria should be stained for examination that still greater magnification as before a portion of the colony is transferred to a drop of water on a slide this is dried in the air and then passed briefly through the flame to fix the preparation to the slide to this fixed preparation called a smear a solution of dye is added to stain the cells after about one minute the excess dye is removed with water the slide is then dried and placed on the stage of the microscope a drop of special oil is placed on the stain smear the lens which permits magnification approximately 1000 times is lowered carefully into the oil upon focusing the stained bacteria are easily seen these are bacilli the rod-shaped forms samples from other colonies show the presence of i which are spherical in shape those with spiral shapes the spiral ax are less frequently found in certain studies special stains may be used to reveal important structures for example the Spore produced by some bacteria permits survival during unfavorable conditions another staining procedure reveals flagella long whip-like structures which enable bacteria to move in a liquid in addition to microscopic examination the characteristics of colonies are used for identification some bacteria produce colonies of specific colors other colonies have unusual surface features a variety of different colonies will be found on nutrient materials exposed to the air for a few minutes frequently on such a plate colonies are found growing together when a smear from a mixed colony is prepared and stained in a special way different bacterial forms are observed these cells represent two different species of bacteria it is possible to separate these forms and to grow each one individually to do this a wire loop is touched to a portion of the mixed colony and streaked lightly across the surface of a sterile nutrient medium after the loop is flamed streaking is continued to distribute the cells following incubation two types of colonies are observed separated on the last streets specially stained smears reveal that each colony consists of a single type of bacterium each bacterium is now isolated and can be grown separately as a pure culture in addition to sell and colony features the metabolism of bacteria is also important in identification for example pure cultures of various bacteria can be transferred or inoculated into nutrient solutions containing a sugar and an acid base color indicator after incubation the breakdown of the sugar by various bacteria is indicated by color changes as compared to the control tube which was not inoculated some bacteria also produce gas which collects in the small inverted - another type of activity can be demonstrated when nutrient agar containing starch is inoculated with test bacteria some bacteria digest starch after growth this can be detected by the addition of iodine the darkening color shows the presence of starch around the bacterial growth the lack of color change indicates that the starch has been digested with an understanding of the requirements for growth and metabolism of bacteria it is possible to devise methods for their control one common method of killing some bacteria is with relatively low heat a series of inoculated tubes is heated at sixty degrees centigrade in a water bath after various time intervals individual tubes are removed and cooled in ice the number of living bacteria in each tube as determined by colony count indicates that fewer cells survive with longer heating ultraviolet radiations from the Sun or an artificial source effect bacteria test organisms are spread over the surface of growth materials the dish partially covered and then exposed to ultraviolet radiation after incubation growth appears only where the bacteria were not exposed to the ultraviolet light Chemical antiseptics also effectively controlled the growth of many bacteria a filter paper disc is soaked in a common antiseptic and placed on growth material that has been inoculated with a large number of bacteria after incubation the clear area around the disc indicates killing of the bacteria which came in contact with the antiseptic even though bacteria are extremely small in size we have seen that methods have been developed for studying their characteristics and activities using these and similar techniques man has learned not only how to control bacteria but also how to utilize their desirable actions in his own service [Music]