MICRO-ORGANISMS 



grapelike clusters (staphylococci), pairs (diplococci), or singly. 



Eocls, vibrios, and spirilla may also be arranged in chains and cl 



of cells, but characteristic names are not commonly used for them. 



Bacteria are ubiquitous. They are found in all types of aoil ai <i 

 are most numerous in fertile soils. They inhabit all the craters of I 

 earth, both fresh and salt, stagnant and free flowing. Thej in 



hot springs and geysers, as well as in arctic and antarctic waters and 

 soils. The surfaces of all plants and animals, as well as intestinal 

 and urinary tracts of animals, are inhabited by bacteria. The air 

 laden with micro-organisms, including bacteria, and they have be 

 recovered even from the air above the North Pole. 



Bacteria are versatile and adaptable. By diligent searching ii i 

 be possible to find strains capable of attacking, and thereby modi i 

 almost any substrate and of growing under almost any set of condi- 

 tions. Life as we know it is impossible without free or dissolved 

 oxygen, except for certain bacteria that cannot grow in its pres 

 These are called anaerobic bacteria. Bacteria that fail to grow unli 

 they have free access to the oxygen of the air are said to be strict 

 aerobes. Still a third group of bacteria, said to be facultative, gr< 

 whether or not gaseous oxygen is available. 



Most bacteria grow at a fairly narrow range of temperatures be- 

 tween 0° and 40° C. However, some can grow at about 55°, but fail to 

 grow if the temperature falls to 30°. Such bacteria are said to be ther- 

 mophilic. The osmotic pressure of body fluids, of lakes, streai 

 rivers, and oceans, and of vegetable juices is ideal for the growth of 

 almost all bacteria, but the halophilic and osmophilic types grow in 

 saturated brines and sirups. 



Although bacteria generally cannot grow if the moisture content 

 drops below 70 percent or if either temperature or osmotic pressure 

 varies too greatly from their optima, some can survive unfavorable 

 conditions because they form spores. Spores are specialized struct ores 

 formed by relatively few bacteria. In spore form some bacteria can 

 even withstand boiling water. For this reason, a temperature of 1- 1 

 C. (250° F.) is used whenever it is desirable to destroy all life, as in 

 preparing surgical instruments, gowns, gloves, and solutions for 

 parenteral administration to patients in hospital and medical pi act ice : 

 as in sterilizing culture media and equipment in microbiology Labors 

 tories; and as in processing foods and beverages In the canning in- 

 dustry. Even then the time of exposure, which is governed by the s 

 and nature of the products to be sterilized, must be at least It) minut 

 usually longer. 



The systematic position of bacteria has long been a eont rover 

 matter. Some authorities believe they belong in the plant kingdom, 

 others in the animal kingdom, and still others in an independent king- 

 dom. Meanwhile, they are generally treated as if they belonged in 

 the plant kingdom. 



Several systems of bacterial classification are in current use. but the 

 one followed by most bacteriologists, especially in the United Sta 

 is the system given in Bergey's Manual of Determinat ive Bacteriology 

 (4). 2 According to it, bacteria are divided into 10 orders, 1 of wh 



2 Italic numbers in parentheses refer to Literature Cited, p. 3 L 



