266 Mary Barber 



similar. This finding has not been confirmed and is rather 

 surprising, since Manson, Pollock and Tridgell (1954) found 

 that penicillinase from B. cereus was immunologically unre- 

 lated to penicillinase from Bacillus suhtilis. 



Current views on the mode of origin of penicillinase - 

 producing staphylococci 



Enzyme adaptation. Most people do not regard contact 

 with penicillin as an important factor in the mode of origin of 

 penicillinase-producing staphylococci. In the early days of 

 penicillin therapy such strains were usually isolated from 

 patients who had never had penicillin, and passage of peni- 

 cillinase-producing strains in the presence of penicillin in vitro 

 causes little or no increase in the production of the enzyme 

 (Bondi et al., 1954). Thus, unlike the penicillinase of B. 

 cereus (Pollock, 1950, 1953), staphylococcal penicillinase is not 

 usually regarded as an adaptive enzyme. 



Selection. In hospitals and other institutions where the use 

 of penicillin is widespread, selection of a few penicillin- 

 destroying strains and the dissemination of these has been 

 shown to be the main reason for the increasing incidence of 

 penicillin-resistant staphylococcal infection (Barber and 

 Rozwadowska-Dowzenko, 1948; Barber and Whitehead, 

 1949; Rountree and Thomson, 1949). In early studies of 

 this kind there was a clear association between penicillinase 

 production and bacteriophage group. Thus, in 1949, Barber 

 and Whitehead in England and Rountree and Thomson in 

 Australia found that most of the strains isolated from peni- 

 cillin-resistant infection belonged to phage-group III. Later 

 penicillinase-producing strains of phage-group I became 

 common, particularly in Maternity Units (Barber, Hayhoe 

 and Whitehead, 1949; Barber and Burston, 1955), and today 

 they are found among all phage-groups (Anderson and 

 Wilhams, 1956). 



Spontaneous mutation. Whatever the importance of selec- 

 tion in the incidence of penicillin-resistant infection, it does 



