Drug Resistance of Staphylococci 267 



not explain the existence of staphylococci with and without 

 the capacity to produce penicillinase. A commonly held view 

 is that this is the result of spontaneous mutation. The sudden 

 emergence from penicillinase-producing staphylococci of cells 

 which have completely lost the capacity to produce the 

 enzyme has been clearly and unequivocally demonstrated, 

 and in a manner which suggests spontaneous mutation (Barber 

 1949; Bondi, Kornblum and Phalle, 1953; Fairbrother, 

 Parker and Eaton, 1954). 



Most investigators, however, have failed to demonstrate 

 penicillin-sensitive staphylococci which have gained the 

 capacity to produce penicillinase in in vitro studies (Bondi 

 and Dietz, 1944; Blair, Carr and Buchanan, 1946; Spink and 

 Ferris, 1947; Barber, 1956). Spink and colleagues (Spink, 

 Hall and Ferris, 1945; Spink and Ferris, 1947) and Blair, 

 Carr and Buchanan (1946) claim that such a change may be 

 induced in vivo by penicillin treatment, but since in neither 

 case were the strains phage-typed it is possible that they were 

 dealing with mixed infections due to penicillin-sensitive and 

 penicillin-resistant strains of different phage-types, which 

 Barber and Whitehead (1949) have shown to be a common 

 occurrence. Penicillin-sensitive and penicillin-resistant strains 

 of the same phage-type have been isolated from a single speci- 

 men of pus (Barber and Whitehead, 1949; Fairbrother, Parker 

 and Eaton, 1954), but this is probably due to the instability 

 of the penicillin-resistant strain, and does not indicate a muta- 

 tion from penicillin sensitivity to penicillinase production. 



It is quite possible that penicillin-sensitive staphylococci 

 do yield penicillinase-producing variants, but the change 

 must be a rare one, and until its occurrence can be unequivoc- 

 ally demonstrated it is impossible to be dogmatic about the 

 mode of origin of such variants. 



Most workers have assumed that the penicillin-sensitive 

 staphylococcus is the original type and the penicillin-destroy- 

 ing strain the mutant, but Fairbrother (1956) suggests that 

 the reverse is more likely. He points out that under "wild 

 conditions" penicillinase might well assist the staphylococcus 



