DEVELOPMENT OF RESISTANCE 



105 



varies with the organism, some losing their 

 resistance rapidly and others only very 

 slowly. Certain strains of bacteria ma_y not 

 become resistant to the drug at all. An 

 organism made resistant to one sulfa com- 

 pound was found to become resistant to 

 others. 



With the introduction of antibiotics for 

 chemotherapeutic purposes, it was soon 

 evident that the problem of bacterial resist- 

 ance would eventually become of paramount 

 importance. It is sufficient to list here a few 

 of the recent contributions to this highly 

 important phase of chemotherapy. Further 

 information is given in the work of Ramsey 

 and Padron (1954), Katsunuma and Xaka- 

 sato (1954), Knight and Collins (1955), Jones 

 et al. (1956), Finland (1958), Chernomordik 

 and Kobeleva (1959), and numerous others. 



The Oxford group of investigators (Chain 

 et al., 1940), in their first report on the use of 

 penicillin for disease control, noted a marked 

 increase in resistance of Staphylococcus 

 aureus to penicillin upon continued use. This 

 observation was soon confirmed by many 

 other investigators and was found to hold 

 true also for certain other organisms natu- 

 rally susceptible to penicillin. The occurrence 

 of the natural \'ariation in resistance of bac- 

 teria to penicillin was also soon recognized. 

 Bacteria acciuire resistance to penicillin when 

 cultivated in a medium containing gradually 

 increasing concentrations of the drug, pro- 

 vided these are kept below the level inhibit- 

 ing bacterial growth. The tolerance of a 

 strain of gonococcus was increased 350 times 

 and of meningococcus 130 times the concen- 

 tration originally permitting growth. The 

 increase in resistance of meningococci to 

 penicillin could also be brought about by 

 passage of the culture through penicillin- 

 treated mice. This increase in resistance was 

 not accompanied by the production of the 

 enzyme penicillinase, which has the capacity 

 of destroying penicillin. 



Considerable variation has been reported 



for the de\'elopment of resistance by bacteria 

 to streptomycin. Of particular importance 

 in this connection is the increased resistance 

 of M. tuberculosis isolated from a host that 

 has been treated with considerable ciuantities 

 of this antibiotic. Variation in sensitivity of 

 E. coli to streptomycin was found to range 

 from 0.3 to 3.0 ^ig per ml, with an a\'erage of 

 1 Mg pel' nil for nine strains. In the case of 

 seven strains of Proteus vulgaris, the varia- 

 tion was from 0.3 to 2.5 fxg per ml. Similar 

 variations were obtained for other bacteria. 

 A strain of Pr. vulgaris made resistant to 

 streptomycin showed only a slight increase 

 in resistance to streptothricin, a closely 

 related antibiotic. 



Bacteria develop resistance to strepto- 

 mycin very rapidly. Among bacteria isolated 

 from the urinary tract, it was found that 

 only three to seven transfers were retiuired 

 to make strains of Pseudomonas resistant to 

 1000 /xg of streptomycin per ml, and between 

 four and se\^en transfers for Streptococcus 

 faecalis. Two strains of E. coli re([uired 7 to 

 12 transfers. .1. cwrogenes and colon-aeroge- 

 nes intermediate strains re(iuired 2 to 17 

 transfers. Proteus strains were sensitive to 

 3.1 to 0.2 /ug of streptomycin per ml, and 

 from 7 to 11 transfers were recjuired to make 

 them resistant to 1000 ^ug per ml. When 

 Proteus was grown in urine, 12 to 24 trans- 

 fers were reciuired to make the l)acteria 

 resistant to 1000 /ig of streptomycin per ml 

 of urine. Proteus splits urea, thus increasing 

 the alkalinity of the medium to more than 

 pH 8, which increases the activity of strepto- 

 mycin. 



Streptomycin-resistant strains showed no 

 change in susceptibility to either penicillin 

 or to sulfonamides. This led to the suggestion 

 that a combination of streptomycin with one 

 of these drugs might prove effective. It was 

 possible to increase the resistance of gram- 

 negative bacteria to more than 50,000 Mg pf^i' 

 ml of streptomycin by passage through in- 

 creasing concentrations of this antibiotic. In 



