Regulatory effects on virulence and phage susceptibility revealed by sdiA mutation in Klebsiella pneumoniae

Sergio Silva-Bea Pablo Maseda Ana Otero ^* Manuel Romero ^*

• Department of Microbiology and Parasitology, Faculty of Biology - Aquatic One Health Research Center (ARCUS), Universidade de Santiago de Compostela, Santiago de Compostela, Spain

The World Health Organization has identified multi-drug resistant Klebsiella pneumoniae strains as the highest priority in 2024. Understanding the regulatory routes of virulence features is crucial for the development of novel anti-virulence strategies. SdiA, a LuxR-like quorum sensing (QS) receptor that responds to N-acyl-homoserine lactones (AHLs), is involved in the regulation of virulence traits in some Gram-negative bacteria. The function of this receptor in the virulence of K. pneumoniae remains uncertain. The objective of the present study was to elucidate the function of SdiA in K. pneumoniae biofilm formation and virulence. To this end, a genetic knockout of sdiA was conducted, and virulence-related phenotypic studies were performed following AHL provision. The results demonstrate that sdiA deficiency increases susceptibility to phage infection and human serum resistance, and promotes biofilm maturation and cell filamentation, although no effect on virulence was observed in vivo in the Galleria mellonella infection model. On the other hand, C6-HSL promoted sdiA-dependent biofilm maturation, capsule production and serum resistance while reducing virulence against G. mellonella in the absence of sdiA. The addition of C6-HSL did not affect phage susceptibility. The results of this study demonstrate that AHLs and SdiA exert a dual influence on virulence phenotypes, operating both independently and hierarchically. These findings provide new insights into the virulence of K. pneumoniae and its regulation by SdiA.