102 Microbes and You 



but one spore is formed by a single cell, there is reproduction 

 without multiplication. This is in contrast to mold spores which 

 are reproductive bodies, many of which are formed by a single 

 mold plant. 



Frequent transplantation under ideal growth conditions may 

 prevent spore-formation, and some strains so cultivated may lose 

 their ability to sporulate even when conditions become unfavorable 

 for the cell. The cause of sporulation is unknown, but it is not 

 necessarily a response to marked unfavorable conditions, since 

 some bacteria sporulate early in their lifetime when conditions are 

 apparently still favorable for microbial growth and multiplication. 

 After the danger has passed, the "possum-like" microbes emerge 

 from their dormancy, or resting stage, and revert to their original 

 vegetative state. The first visible change when spores are placed 

 in a suitable medium is an enlargement of the spore, probably due 

 to the absorption of water. After losing its refractive nature, the 

 spore elongates. Some shed their "skin" as they germinate, while 

 others appear to absorb the spore material. There is some evidence 

 that the "shedding" type of spore can withstand more unfavorable 

 environmental conditions than can the "absorbing" type. 



A given species of organism will exhibit a constant size, shape, 

 and location of the spore (terminal, suhterminal, or central) within 

 the cell, and in some cases this structure aids in the tentative identi- 

 fication of an organism. Should the swelling occur in the center of 

 the rod, it gives a spindle-shaped appearance, and if the bulge 

 is located terminally, the cell takes on a drumstick shape. 



Not all spores are equally resistant to chemical and physical 

 forces, but the most resistant spores are the basis for the time and 

 temperature relationships employed in sterilization technics. Were 

 there no spores, we could drastically revise our sterilizing tem- 

 peratures downward. The common soil organism Bacillus stib- 

 tilis has been found to withstand 100° C. dry heat for three 

 hours, and Clostridium hotulinum, the causative a2;ent in a highly 

 fatal type of food poisoning to be discussed in a later chapter, 

 may withstand four or five hours of boiling. The spores of some 



