Host Soluble Factors Cause Changes in Antibiotic Susceptibility and Biofilm Formation Ability.

is a major nosocomial pathogen with a remarkable ability to adhere to the surfaces of indwelling medical devices and form biofilms. Unlike other nosocomial pathogens, the interaction of with host factors has not been the focus of substantial research. This study aimed to assess the alterations in the antibiotic susceptibility and biofilm formation ability of in the presence of host serum factors. strain RP62A was cultured in a laboratory culture medium with or without human serum/plasma, and changes in antibiotic susceptibility, biofilm formation, and gene expression were evaluated. The data obtained revealed that exposure to host serum factors increased the susceptibility of to glycopeptide antibiotics and was also detrimental to biofilm formation. Gene expression analysis revealed downregulation of both and genes shortly after human serum/plasma exposure. The importance of transferrin-mediated iron sequestration as a host anti-biofilm strategy against was also emphasized. We have demonstrated that serum factors play a pivotal role as part of the host's anti-infective strategy against infections, highlighting the importance of incorporating such factors during in vitro studies with this pathogen.