Drug Resistance in Bacteria 17 



(1954) found that some penicillin-resistant forms of bacteria 

 take up more and some take up less of the drug than the 

 sensitive forms. 



These facts support the idea that there may be more than 

 one mechanism of resistance. If the cell has suffered damage 

 (e.g. by exposure to radiation) so that it has lost receptors 

 which bind the drug, then it may thereby acquire a certain 

 passive kind of resistance which would contrast with a more 

 active type of resistance to be suspected in those examples 

 where the drug is actually taken up more readily by the 

 adapted form. 



The passive type due to loss of a function would be that for 

 which a spontaneous origin could be most readily explained. 



Among drug resistances, as distinct from resistance to 

 phage, that to streptomycin seems more likely than many to 

 have, on occasion though not necessarily always, a spon- 

 taneous origin. In this connexion the adsorption isotherms 

 are of interest. Dean (unpublished) found that the sensitive 

 form of Bad. lactis aerogenes took up streptomycin according 

 to a conventional type of adsorption isotherm. A resistant 

 strain took up little or none in most experiments, but occasion- 

 ally showed a positive adsorption. If the resistant bacteria 

 were grown anaerobically, however, the adsorption was once 

 more considerable. The phenomena are still under investiga- 

 tion but they seem, on the whole, to provide evidence that loss 

 of receptors may play some part in one type of streptomycin 

 resistance of at least some bacteria. 



The complexity of the situation is, however, illustrated by 

 the fact that Neumark and Pasynskii (1954) found about 

 equal adsorptions of streptomycin for resistant and sensitive 

 varieties of the same strain of Staphylococcus aureus. 



Papilla Formation 



The papillae or secondary colonies which, in certain con- 

 ditions, form on the edge or on the surface of primary colonies 

 have generally been supposed to owe their origin to mutant 



