Action of 8-azaguanine and 8-azaxanthine on Pseudomonas aeruginosa

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Abstract
8-Azaguanine does not inhibit the growth of P. aeruginosa, but undergoes slow deamination. 8-Azaxanthine temporarily arrests the growth of this species. This growth retardation is abolished by hypoxanthine, xanthine and a number of unnatural purines. During growth inhibition by azaxanthine, the xanthine-oxidase-like activity of the bacterial cells is enhanced. Much larger increments of enzymic activity are obtained by the addition of hypoxanthine, xanthine or certain unnatural purines, which all contain an unsubstituted imidazole ring. During growth inhibition by 8-azaxanthine, the urate-oxidase-like activity of the bacteria is strongly depressed. The addition of hypoxanthine or xanthine to the culture medium produces a huge increase in the enzymic activity of the normal strain. After the first exposure to 8-azaxanthine, a resistant strain emerges which shows normal xanthine-oxidase and urate-oxidase activity, even when growing in the presence of the antimetabolite. Benzimidazole and benzotriazole are weak growth inhibitors. They depress xanthine-oxidase activity of the bacterial cells, but leave their urate-oxidase activity unaffected.