180 ANTIBACTERIAL SUBSTANCES FOR TREATMENT OF INFECTIONS 



or by the addition to the medium of traces of zinc, which, by catalysing the complete 

 oxidation of the dextrose, prevents the accumulation of gluconic acid, a product of incom- 

 plete oxidation of the dextrose (Foster, WoodruflF and McDaniel 1943). P. notatum 

 throws variants during its growth in stock cultures, and it is essential to maintain a master 

 culture of high penicillin-producing capacity. In fluid cultures, P. notatum grows as 

 a felt on the surface of the medium, with consequent limitations in the exposure of the 

 growing mould to air and to the nutrients in the fluid. Clifton (1943) introduced a method 

 resembling that used in the commercial process for the rapid production of vinegar, in 

 which the culture is kept continuously trickling over wood shavings packed in an aerated 

 columnar container. Improved methods of fractionation, including chromatographic 

 methods, have also improved the yield from crude culture filtrates (Abraham, Chain and 

 Hohday 1942). 



Bacteriological Aspects. Fleming's original observations on the range of in 

 vitro activity of penicillin have been amply confirmed. Staph, aureus, Str. pyogenes, 

 N. meningitidis and N. gonorrhoeae, the gas-gangrene Clostridia and Actino. bovis 

 are among the most susceptible ; pneumococci and Str. viridans a little less so. 

 If we take the amount of penicillin required to inhibit a certain number of sus- 

 ceptible Staph, aureus as unity, the inhibiting dose for these other bacteria lies 

 between 0*25 and 4. C. diphtherice is slightly less susceptible, the dose being 

 from 10-30 ; for Str. fcecalis, Salm. enteritidis and Br. abortus and melitensis, it is 

 from 30-100 ; for Proteus vulgaris, Sh. shigce. Past, pestis, 150-500 ; for Bad. coli, 

 aerogenes and friedldnderi, 1,000-16,000 ; and for Mgco. tuberculosis, Ps. pyocyanea, 

 L. icterohcemorrhagice, V. cholerce, Hemophilus, yeasts and moulds, the inhibiting 

 dose is of this order, or higher (Bornstein 1940, Abraham et al. 1941, Florey and 

 Jennings 1942, Hobby, Meyer and Chaffee 1942a, McKee and Kake 1942rt, McKee, 

 Hamre and Kake 1943, McKee, Rake and Menzel 1944, Helmholz and Sung 1944). 

 Ery. monocytogenes {ListereUa) resists doses of 40 (Foley, Epstein and Lee 1944). 

 These figures are for the most part determined for a few strains only, and as might 

 be expected, the inhibiting dose varies from strain to strain in a species. Thus, 

 it may vary up to 25-fold for pneumococci, and up to 100-fold for Staph, aureus. 



Bacteria may be trained to grow in graduaUy increasing concentrations of peniciUin. 

 By this method the resistance oi Staph, aureus may be increased up to a 1,000-fold (Abraham 

 et al. 1941). Rammelkamp and Maxon (1942) reported a 64-fold mcrease in strains 

 habituated to peniciUin in vitro, and uja to a 100-fold increase in strains from four of 

 fourteen patients treated with peniciUin (see also McKee and Houck 1943). PeniciUin- 

 resistant pneumococci have been induced in vivo by passage through peniciUin-treated 

 mice. The resulting strains were resistant in vitro, and remained so after 30 passages 

 through normal mice (Schmidt and Sesler 1943). By simUar means. Rake and his col- 

 leagues (Rake et al. 1944) induced resistance in Staph, aureus and pneumococci. It should 

 be noted that resistance induced in vivo is not necessarily due to an increased insusceptibihty 

 to peniciUin, for Rake and his coUeagues found that one strain of Staph, aureus, when 

 passed through peniciUin-treated mice, gained in mouse-virulence, but its in vitro resistance 

 was unchanged ; the strain had clearly adapted itself to the antibacterial action of the 

 mouse tissues, but not to the antibacterial action of peniciUin. 



Solutions of peniciUin exposed to air rapidly lose their potency, owing to contamination 

 by bacteria, micrococci, and bacilU of various kinds that elaborate enzymic substances 

 destroying the peniciUin. Abraham and Chain (1940) described a penicUUnase in Bad. 

 coli, and a simUar substance has been described in paracolon baciUi (Harper 1943), in 

 certain naturaUy insensitive strains of Staph, aureus (Kirby 1944), and in B. subtilis 

 (Ungar 1944, Duthie 1944). These enzymic substances are found in filtrates, cultures 

 and extracts of the bacteria. They are relatively stable. Their relation to the structure 

 of peniciUin and of penicUUn-like substances is not yet known. At present, their interest 



