Drug Resistance of Staphylococci 265 



branes with an average pore diameter of 0-68 [x, the filtrates 

 were found to have considerable penicillin-destroying activity, 

 although less than (in one experiment seven-tenths) that of 

 unfiltered cultures. Although the enzyme could be refiltered 

 through gradocol membranes without loss of activity it was 

 adsorbed onto Seitz, Berkefeld and glass filters. 



The resistance to penicillin exhibited by penicillinase- 

 producing staphylococci appears to be almost entirely due to 

 the enzyme. Individual cells of these strains have a sensitivity 

 to penicillin similar to or slightly less than that of typical 

 penicillin-sensitive cultures. The degree of resistance, there- 

 fore, depends on the amount and rate of penicillinase produc- 

 tion, and in laboratory tests may vary many hundred-fold 

 according to the size of inoculum used (Luria, 1946; Barber, 

 1947; Gilson and Parker, 1948; Bondi and Dietz, 1948; 

 Barber and Whitehead, 1949). 



The production of penicillinase by staphylococci is inhibited 

 by sub-bacteriostatic concentrations of sodium azide, but this 

 agent does not inactivate the cell-free enzyme (Dietz and 

 Bondi, 1948). The enzyme itself is inhibited "at least tem- 

 porarily" by 1 per cent sodium benzoate or sodium sulphan- 

 ihde (Reid, Felton and PitrofF, 1946). Staphylococcal peni- 

 cillinase is very sensitive to high temperatures, and Bondi, 

 Kornblum and Phalle (1953) and Fairbrother, Parker and 

 Eaton (1954) found that growth at 44° accelerated the 

 natural tendency of penicillinase-producing staphylococci to 

 yield penicillin-sensitive variants. 



Penicillinase from certain bacteria has been shown to be 

 antigenic. Perlstein and Liebmann (1945a and b) inoculated 

 rabbits with a cell-free preparation of penicillinase from an 

 unidentified Gram-negative bacillus, and obtained an anti- 

 serum which inhibited the action of the enzyme against peni- 

 cillin. Housewright and Henry (1947) found that a rabbit 

 anti-serum prepared against penicillinase isolated from a 

 strain of Bacillus cereus inhibited the action of penicillinase 

 from a strain of Staph, aureus as well as from B. cereus, and 

 concluded that the two enzymes were immunologically 



