Shepard, G. E. | bioRxiv Science

bioRxiv2026

Phenotypic heterogeneity and kidney tropism of Klebsiella pneumoniae clinical urinary tract infection isolates

Urinary tract infections (UTIs) are a significant public health burden that impact millions of people every year and are highly prevalent among in hospital-acquired infections. Klebsiella pneumoniae is the second most common cause of UTIs after uropathogenic Escherichia coli (UPEC). Thus far, the molecular mechanisms underlying pathogenesis is better understood in UPEC than K. pneumoniae. UPEC is known to have fitness factors such as fimbrial adhesion and evasion of complement-mediated killing. In other infection types, K. pneumoniae fitness has been associated with mucoidy and diverse capsular serotypes. To establish K. pneumoniae virulence factors contributing to UTI, we examined how environmental cues regulate urovirulence-associated phenotypes in clinical K. pneumoniae UTI strains. These factors included capsular polysaccharide properties, hemagglutination, serum resistance, adherence to bladder epithelial cells, and in vivo fitness. We found that clinical K. pneumoniae UTI isolates phenotypes are highly heterogeneous and can change in response to human urine. Despite K. pneumoniae clinical isolates presenting heterogeneous fitness properties, all similarly colonize the urinary tract. These results suggest that additional fitness factors contribute to K. pneumoniae uropathogenesis. Identifying these shared fitness factors will provide mechanistic insights into Klebsiella uropathogenesis and reveal candidate therapeutic targets.

microbiology↗

bioRxiv2024

Arginine Regulates the Mucoid Phenotype of Hypervirulent Klebsiella pneumoniae

Hypervirulent Klebsiella pneumoniae is associated with severe community-acquired infections. Hypervirulent K. pneumoniae colonies typically exhibit a mucoid phenotype. K. pneumoniae mucoidy is influenced by a complex combination of environmental factors and genetic mechanisms. Mucoidy results from altered capsular polysaccharide chain length, yet the specific environmental cues regulating this phenotype and their impact on pathogenesis remain unclear. This study demonstrates that casamino acids enhance the mucoidy phenotype but do not affect total capsular polysaccharide levels. Through targeted screening of each amino acid present in casamino acids, we identified that arginine is necessary and sufficient to stimulate the mucoid phenotype without altering capsule abundance. Furthermore, arginine activates the rmpADC promoter, increasing rmpD transcript levels, which in turn modulates capsular polysaccharide chain length and diversity. The arginine regulator, ArgR, plays a pivotal role in this regulatory cascade since deleting argR decreases mucoidy and increases capsular polysaccharide chain length diversity. Additionally, the {Delta}argR mutant displays increased macrophage association and has a substantial competitive defect in the lungs of mice, suggesting a link between arginine-dependent gene regulation, immune evasion and in vivo fitness. We discovered that arginine-dependent regulation of mucoidy is conserved in four additional hypervirulent K. pneumoniae isolates likely via a conserved ARG binding box present in rmp promoters. Our findings support a model in which arginine activates ArgR and increases mucoidy in hypervirulent K. pneumoniae. As a result, it is possible that arginine-dependent regulation of mucoidy allows hypervirulent K. pneumoniae to adapt the cell surface across different niches. This study underscores the significance of arginine as a regulatory signal in bacterial virulence. IMPORTANCEThe rise of hypervirulent Klebsiella pneumoniae as a global health threat underscores the urgent need to understand its pathogenic mechanisms. Its ability to cause severe infections in healthy individuals and spread beyond the endemic Asia-Pacific region demands a deeper investigation into the mechanisms driving hypervirulence. The hypermucoid phenotype is primarily associated with hypervirulent isolates and is regulated by RmpD, which increases capsular polysaccharide chain length and uniformity. Understanding how environmental and genetic factors influence mucoidy is vital for elucidating the mechanisms by which K. pneumoniae adapts and thrives in different ecological and host niches. Our study defines the role of amino acids, particularly arginine, in regulating the bacterial surface by modulating rmpD expression. These results reveal that mucoidy is not a constitutive phenotype, but rather a dynamic process finely tuned by nutrient availability. Our findings expand our understanding of how the rmp locus is controlled and how changes in arginine availability may optimize K. pneumoniae immune evasion.

microbiology↗