SUMMARY: The growth of strain / on nutrient agar is the same as in broth with regard to the initial lag period and the rate of increase during the exponential phase. On nutrient agar, growth is finally slowed down either when individual colonies contain more than 2 bacteria, or when the total number of bacteria/4 in. plate exceeds 10.

The rate of mutation to phage resistance was measured by a modification of Demerec’s method of spraying plate cultures with a phage aerosol, and counting resistant survivals. With the phage 1, after twelve bacterial generations on nutrient agar at 37°, the value of 0·74 ± 0·04 mutations/10 bacterial divisions was obtained, and after eighteen bacterial generations, 0·70 ± 0·04.

Resistance to 1 phage is probably brought about by at least five separate mutations, as shown by tests of resistance to other phages. Different strains of yield different proportions of some of these mutants. Thus strain / yielded a lower proportion of the mutant /1 than did strain . Furthermore, as different strains of 1 phage may contain varying amounts of the phage mutant 1, capable of lysing the bacterial mutant /1, but not /1, 5, variations in the relative proportions of /1 and /1, 5 may also occur when different samples of phage are used. Consequently, constancyof mutation rate can only be guaranteed for given cultures of both bacteria and phage.


Article metrics loading...

Loading full text...

Full text loading...



  1. Demerec M. 1946; Induced mutations and possible mechanisms of the transmission of heredity in Escherichia coli. . Proc. nat. Acad. Sci., Wash. 32:36
    [Google Scholar]
  2. Demerec M., Fano U. 1945; Bacteriophage-resistant mutants in Escherichia coli. . Genetics 30,:119
    [Google Scholar]
  3. Luria S. E. 1945; Mutations of bacterial viruses affecting their host range. Genetics 30,:84
    [Google Scholar]
  4. Luria S. E., Delbrück M. 1943; Mutations in bacteria from virus sensitivity to virus resistance. Genetics 28:491
    [Google Scholar]
  5. Mayr-Harting A. 1947; The growth of bacterial colonies and their viable population. J. Hyg., Comb 45:19
    [Google Scholar]
  6. Within E. M. 1946; Inherited differences in sensitivity to radiation in Escherichia coli.. Proc. nat. Acad. Sci., Wash 32:59
    [Google Scholar]

Data & Media loading...

This is a required field
Please enter a valid email address
Approval was a Success
Invalid data
An Error Occurred
Approval was partially successful, following selected items could not be processed due to error