What historical contribution is Paul Ehrlich credited with in antimicrobial development?

Creating the first synthetic broad-spectrum antifungal used widely in hospitals during the 1920s

Discovering penicillin from a mold contaminant in a Petri plate and proving it cured bacterial infections

Proposing the "magic bullet" concept and developing an early chemotherapeutic agent to treat syphilis

Showing that viruses could be selectively killed with metal salts without host damage