The “instant evolution” system was initially developed in E. coli, primarily because of the ease with which this organism can be genetically manipulated. Because many of the functionally important regions of rRNA are conserved among bacteria, drug leads developed against conserved targets in the E. coli system may produce broad-spectrum anti-infectives. In order to develop a system to produce narrow-spectrum anti-infectives, herein we disclose methods for identifying functional mutant P. aeruginosa ribosomes suitable as drug targets and for identifying drug candidates that do not bind to the human 16S rRNA.