JT71 is a small-molecule inhibitor of the bacterial transcription regulator MrkH, showing potent anti-biofilm and anti-virulence activity in both in vitro and in vivo-relevant infection models. In vitro, JT71 inhibits MrkH-mediated transcription of the mrkA operon and suppresses type 3 fimbriae production in Klebsiella pneumoniae, resulting in ~50% reduction of mrkA promoter activity at 50 μM without affecting bacterial viability. It significantly reduces biofilm formation across multiple clinical and multidrug-resistant K. pneumoniae isolates as well as Citrobacter koseri, and downregulates both mrkH and mrkA expression, confirming dual transcriptional suppression. Mechanistically, JT71 binds to MrkH and interferes with c-di-GMP–dependent activation and/or DNA-binding activity, disrupting fimbriae assembly and surface adhesion.
