. Ciba Foundation symposium on drug resistance in micro-organisms: mechanisms of development. Drug resistance in microorganisms. Inheritance in Single Bacterial Cells 65 to the satisfaction of other workers who had a bias in favour either of adaptation or of major mutation as the basis for bacterial variation. If single cells are cultured and from the clone further single cells are selected these will differ from one another in anti- biotic sensitivity (Fig. 1). The differences here are so small. 0-05 0-5 5-0 log penicillin concentration () Fig. 2. Results of tube titration of sensitivit
. Ciba Foundation symposium on drug resistance in micro-organisms: mechanisms of development. Drug resistance in microorganisms. Inheritance in Single Bacterial Cells 65 to the satisfaction of other workers who had a bias in favour either of adaptation or of major mutation as the basis for bacterial variation. If single cells are cultured and from the clone further single cells are selected these will differ from one another in anti- biotic sensitivity (Fig. 1). The differences here are so small. 0-05 0-5 5-0 log penicillin concentration () Fig. 2. Results of tube titration of sensitivity of single-cell strains of staphylo- cocci. Key to curves: , strain I; , strain Via; —O—» strain XXX«; , strain XXXIa. The four subcultures show a similar distri- bution of sensitivity, although the average sensitivity of each is at a different level. Each curve on this is built up from 11 separate points, the only 3 points not falling on their line are marked «. (Hughes, W. H. (1952), J. gen. Microbiol., 6, 175.) that had the titration not been repeated on several occasions with different batches of penicillin over intervals of many months the author would not have been convinced that they were not due purely to experimental error. If now from the tail of the population the more resistant cells are picked, new populations with increased resistance are obtained. Fig. 2 shows the stages of the investigation. It will be seen that the increase is fairly steady. This impression can be misleading since only the most resistant population is DRUG RES.—3. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Ciba Foundation; Wolstenholme, G. E. W. (Gordon Ethelbert Ward); O'Connor, Cecilia M. (Cecilia Mary), 1927-. Boston, Little, Brown
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