Activity of RX-04 Pyrrolocytosine Protein Synthesis Inhibitors against Multidrug-Resistant Gram-Negative Bacteria.

Pyrrolocytosines RX-04A to -D are designed to bind to the bacterial 50S ribosomal subunit differently from currently used antibiotics. The four analogs had broad anti-Gram-negative activity: RX-04A-the most active analog-inhibited 94.7% of clinical Enterobacteriaceae , Acinetobacter baumannii , and Pseudomonas aeruginosa at 0.5 to 4 μg/ml, with no MICs of >8 μg/ml. MICs for multidrug-resistant (MDR) carbapenemase producers were up to 2-fold higher than those for control strains; values were highest for one Serratia isolate with porin and efflux lesions. mcr-1 did not affect MICs.