CHAPTER XX 



COLIGINS AND OTHER BAGTERIOGINS* 



1. Definition and Criteria 



a. Definition 



In 1925, Gratia discovered that the filtrates of cultures of a 

 particular strain of Escherichia coli strongly inhibited the growth 

 of another strain of the same species. The inhibitory substance, 

 to which the name colicin was later given (Gratia and Fred- 

 ericq, 1946), diffused in agar and through cellophane mem- 

 branes, was resistant to heat and to the action of chloroform, pre- 

 cipitated in acetone, and was apparently not antigenic. 



In his early publications, Gratia (1932) drew a parallel be- 

 tween bacteriophages and colicins. Like bacteriophages, coli- 

 cins are highly specific. In particular, colicinogenic bacteria 

 are resistant to the action of the colicin they produce. From 

 sensitive cultures, resistant derivatives can be isolated. But an 

 essential difference exists between phages and colicins: whereas 

 the former are reproduced by sensitive bacteria the latter are not. 



The production of colicin by colicinogenic bacteria is also very 

 similar to the production of phage by lysogenic bacteria. The 

 amount of colicin produced increases during the growth of the 

 culture. Every single bacterium is able to give rise to a colicino- 

 genic culture. When plated on the sensitive indicator, colicino- 

 genic bacteria form minute colonies surrounded by a halo which 

 closely resembles a plaque. 



Since Gratia's original observations analogous substances have 

 been found by Fredericq to be produced by numerous strains of 

 the Enter ohacteriaceae family, including Escherichia^ Aerobacter, 



* Chapter contributed by F. Jacob and E.-L. Wollman. 



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