124 Microbes and You 



the medium, the spreading of Proteus can be prevented and dis- 

 crete colonies may be more readily examined for some of the cul- 

 tural characteristics mentioned previously. 



Bacteria, like humans, vary in their food demands. A person 

 who has been on a diet of filet mignon finds it difficult to switch 

 to a steady diet of pork and beans. Some bacteria are also very 

 fastidious about what they will eat, and if they are deprived of 

 their high living, they would prefer not to put up a struggle to 

 change their mode of life, and in other instances they may be pre- 

 vented from doing so. The "vampire-like" Hemophilus (blood- 

 loving) group of bacteria, including the organism which causes 

 whooping cough (Hemophilus pertussis), is incapable of growing 

 unless it has access to blood and blood derivatives. The more 

 parasitic an organism becomes, the more exacting it may be in its 

 food demands. When viruses are discussed, you will discover that 

 not only must viruses have cells upon which to grow, but they 

 must have living cells, and sometimes even particular living cells 

 from designated tissues. Such extreme dependency limits chances 

 for survival of many parasitic organisms when the environment is 

 altered. 



MICROMANIPULATORS FOR SINGLE CELL ISOLATION 

 At times, particularly in research investigations involving the 

 genetics of bacteria, it becomes desirable to isolate single bacterial 

 cells to insure the purity of a given strain of organism under in- 

 vestigation. This type of isolation is not practical on a routine 

 basis, but its mention should be included in a discussion of technics 

 employed for obtaining pure cultures of bacteria. 



By placing a series of small drops of diluted liquid culture on 

 a slide and examining them with the aid of a microscope to find 

 a drop containing only a few bacteria (or only one), it is possible 

 with the aid of a micromanipulator to isolate an organism from its 

 fellow microbes in that fluid drop. Without going into the minute 

 details as to the operation of this microscope attachment, the tech- 

 nic involves drawing isolated organisms into a fine capillary pi- 

 pette and transferring the trapped cells into a suitable broth 



