H-NS enhances phage resistance in Klebsiella pneumoniae by suppressing quorum sensing

The molecular mechanisms underlying <i>Klebsiella pneumoniae</i> (KP) resistance to phages have not been fully elucidated, especially those involving the quorum-sensing (QS) system and the global regulator H-NS. In this work, we investigate the relationship between H-NS and QS in phage resistance by detecting transcriptional variation under phage pressure with RT-qPCR. <i>LuxS</i> and <i>lsr</i> operon knockout strains are generated via CRISPR editing, and H-NS-overexpressing mutants are constructed using plasmid-based overexpression. We also determine phage susceptibility by measuring the efficiency of plating (EOP). The capsular uronic acid content and phage adsorption efficiency are evaluated. The results show that phage pressure strongly downregulates <i>luxS</i> and <i>lsr</i> operon gene expressions but upregulates the transcription of H-NS. Knockout of either <i>luxS</i>/ <i>lsr</i> operon genes or overexpression of H-NS results in diminished phage sensitivity and the downregulation of CPS synthase genes. However, these changes do not reduce the capsular uronic acid content or affect phage adsorption rates, suggesting that H-NS-mediated resistance is independent of capsular modulation. In addition, this H-NS-QS regulatory link is conserved between HvKP and CRKP. H-NS enhances phage resistance by suppressing QS through a mechanism independent of capsular polysaccharide modulation, as evidenced by unaltered phage adsorption and statistically insignificant changes in capsular uronic acid. This provides a novel explanation for a resistance mechanism involving intracellular defenses ( <i>e</i>. <i>g</i>., abortive infection) and provides possible avenues for improving phage therapy targeting multidrug-resistant <i>K</i>. <i>pneumoniae</i>.