560 5. QUINONES 



active, the bacteriostatic concentration being 0.0047 mM. As the sodium 

 sulfonate this compound was designated "antibrucellin" and found to be 

 well tolerated by various routes. Successful treatment of 25 of 29 cases 

 of human brucellosis was reported (Del Vecchio, 1948 b). 



EFFECTS ON FUNGI AND YEASTS 



Certain quinones have been widely used as agricultural fungicides for 

 the past 30 years. Halogenation markedly increases the antifungal potency 

 of quinones and the two most commonly used compounds commercially 

 are chloranil (Spergon) and 2,3-dichloro-l,4-naphthoquinone (Dichlone, 

 Phygon). They are applied to seeds, seedlings, and adult plants to control 

 various rusts, rots, mildews, wilts, and blights due to fungi in legumes, fruit 

 trees, ornamental plants, and various vegetables. At the proper concentra- 

 tions they will usually suppress the fungi without damaging the plants, but 

 occasionally they may discolor fruits or leaves. The quinones have not been 

 found to be useful in clinical mycoses, mainly because they are irritant to 

 human tissues. Some results on the inhibition of fungal growth are summar- 

 ized in Table 5-10. Two facts are immediately evident: (1) fungi and yeasts 

 are very susceptible to certain quinones, particularly the chlorinated deri- 

 vatives, and are often inhibited at concentrations of 0.0001-0.001 mM; 

 and (2) the relative potencies against fungi and yeasts are quite different 

 from those observed in the inhibition of bacterial growth. As is frequently 

 the case with bacteria, growth stimulation is usually observed at low con- 

 centrations of certain quinones. It has been shown that p-benzohydroqui- 

 none can serve as the carbon source for the growth of Aspergillus oryzae 

 (Tamiya, 1932), and that Aspergillus niger metabolizes the hydroquinone 

 to keto acids (since /?-ketoadipate accumulates in the presence of arsenite), 

 which are decarboxylated and oxidized (Friedrich, 1956), but whether 

 such utilization is related to the growth stimulation is not known. The 

 fungi are similar to bacteria in that they are killed only by much higher 

 concentrations than are required to inhibit the growth, differences around 

 100-fold in the cidal and static concentrations being common. It must also 

 be remembered that fungi often possess active enzyme systems for the deg- 

 radation of substances not attacked by bacteria, and thus destruction of 

 the inhibitors may in some instances have reduced the potency, the figures 

 in the table thus being occasionally too high. Rich and Horsfall (1954) 

 suggested that one factor determining the susceptibilities of fungi to both 

 polyphenols and quinones might be the content of polyphenol oxidase, 

 and presented some evidence based on a study of 42 compounds that such 

 a correlation may exist. Two other factors controlling the susceptibility 

 of fungi to quinones are the pH (F. G. Smith et al., 1946) and temperature 

 (Molho and Lacroix, 1949). The inhibition of the growth of Glaucoma piri- 



