DRUG RESISTANCE OF STAPHYLOCOCCI 

 WITH SPECIAL REFERENCE TO 

 ^ PENICILLINASE PRODUCTION 



Mary Barber 



St. Thomas's Hospital Medical School, London 



Penicillin-resistant strains of staphylococci are many 

 and varied. According to their response to the antibiotic they 

 fall into three distinct groups: (1) drug-tolerant, (2) drug- 

 dependent and (3) drug-destructive. Organisms of the first 

 group are capable of growing in the presence of an increased 

 concentration of the antibacterial agent, which remains 

 unchanged and retains full activity for other bacteria; the 

 growth of organisms of the second group is actually favoured 

 by or even completely dependent on the presence of the 

 antibiotic ; organisms of the third group produce an antagonist 

 which inactivates the antibiotic. Penicillin-tolerant and peni- 

 cillin-dependent strains occur in in vitro studies; penicillin- 

 destroying strains, on the other hand, are the cause of peni- 

 cillin-resistant staphylococcal infection. 



Penicillin-tolerant strains are isolated with great frequency 

 w^hen penicillin-sensitive staphylococci are passaged in the 

 presence of penicillin in vitro (Barber, 1953a). The increase 

 in resistance to penicillin occurs gradually and is lost in a 

 similarly gradual fashion if the strain is passaged in the ab- 

 sence of penicillin. Resistant strains of this type usually show 

 morphological variations and an increase in the lag phase 

 of growth; on solid medium they often yield tiny semi-trans- 

 parent colonies (Barber, 1953a and b). They are also de- 

 ficient in coagulase and a-toxin production and, probably for 

 this reason, are of lowered virulence (Rake et al., 1944; 

 Spink, Ferris and Vivino, 1944; Blair, Carr and Buchanan, 



