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It is a known fact that bacteria develop immunity to antibiotics. Why then did not all bacteria develop immunity to natural antibiotics like penicillin in the fungi?
It is for sure that fungi did not care to continue killing all bacteria so that them won't be able to develop immunity (as we're adviced today to use antibiotics carefully, in order not to develop a superinfection)..
Looking at all the time span that bacteria and fungi exist, it seems unlikely that there'd be any bacteria left not yet immune to penicillin at all. However, that's not the case, the antibiotic is still a rather successful one.