1950 Geloof en Wetenschap : Orgaan van de Christelijke vereeniging van natuur- en geneeskundigen in Nederland - pagina 24

16

Dr A TH KNOPPERS

Vervolgens trachtte D e m e r e c met de z.g. ,,fluctuatie-test" een oplossing te vinden voor de vraag hoe de stammen ontstaan Dit experiment is 20 fraai en zo exact, dat het hier letterlijk wordt overgenomen : ,,In the majority of experiments reported in this paper, bacteria were m contact with penicillin only during the time when the test for resistance was being earned on Otherwise they were grown m the broth medium free of penicillin If the resistance is induced through interaction between bacteria and penicillin when they are in contact with each other, it would be expected that approximately similar numbers of resistant bacteria would be obtained when samples containing similar numbers of bacteria are plated onto nutrient agar containing a certain concentration of penicillin, irrespective of the origin of these samples The situation would be quite different in the event that the origin of resistance is mutational In such case, one would expect to obtain similar numbers of resistant colonies only in samples taken from the same culture If, however, each of the samples came from a separate culture and mutations occur at random, then one would expect to obtain a large number of resistant colonies from cultures m which mutation happened to occur early m the growth of the culture and a small number of resistant colonies from cultures m which mutation happened to occur late provided resistant bacteria grow more or less like the normal ones If resistance originates by mutation, then, the variation m number of resistant bacteria between samples taken from separate cultures should be much greater than between samples taken from the same culture A critical experiment to distinguish between these two possibilities was planned as follows A saturated broth culture of bacteria was diluted to lO-*», so that the broth contained about 300 bacteria per cc 0 3 cc of this was placed m each of 30 small test tubes One large test tube containing about 15 cc of broth was inoculated with another sample of 0,3 cc from the same dilution. All 31 test tubes were incubated at 37 C for 18 hours, and precautions were taken to prevent evaporation from the tubes containing the small cultures After 18 hours of incubation, 0,7 cc. of broth was added to each of these 30 small tubes m order to reduce the error when the contents of each tube were taken out and plated The number of bacteria was determined by sampling 10 of the small tubes, taking 0,05 cc of material from each and assaying it on nutrient

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