In Vitro Activity Analysis of a New Polymyxin, SPR741, Tested in Combination with Antimicrobial Agents Against a Challenge Set of Enterobacteriaceae, Including Molecularly Characterized Strains.

The activities of azithromycin, fusidic acid, vancomycin, doxycycline, and minocycline were evaluated alone and in combination with SPR741. A total of 202 Escherichia coli and 221 Klebsiella pneumoniae isolates were selected, and they included a genome-sequenced subset ( n = 267), which was screened in silico for β-lactamase, macrolide-lincosamide-streptogramin (MLS), and tetracycline ( tet ) genes. Azithromycin (>16 mg/liter), fusidic acid (>64 mg/liter), vancomycin (>16 mg/liter), and SPR741 (>8 mg/liter) showed off-scale MICs when each was tested alone against all isolates.