Staphylococcus aureus Biofilms and Their Response to a Relevant in vivo Iron Source

Abstract

Biofilm infections can be chronic, life threatening and challenging to eradicate. Understanding in vivo stimuli affecting the biofilm cycle is one step toward targeted prevention strategies. Iron restriction by the host is a stimulus for biofilm formation for some Staphylococcus aureus isolates; however, in some infection scenarios bacteria are exposed to abundant amounts of hemoglobin (Hb), which S. aureus is able to use as iron source. Thus, we hypothesized a role for Hb in the biofilm infection. Microplate “biofilm” assays showed biofilm-matrix production was increased in the presence of hemoglobin when compared to the provision of iron as an inorganic salt. Microscopic analysis of biofilms showed that the provision of iron as hemoglobin consistently caused thicker and more structured biofilms when compared to the effect of the inorganic iron source. Iron responsive biofilm gene expression analysis showed that Agr Quorum Sensing, a known biofilm dispersal marker, was repressed with hemoglobin but induced with an equivalent amount of inorganic iron in the laboratory strain Newman. The gene expression of two biofilm structuring agents, PSMα and PSMβ, differed in the response to the iron source provided and was not correlated to hemoglobin-structured biofilms. A comparison of the model pathogen S. aureus Newman with local clinical isolates demonstrated that while there was a similar phenotypic biofilm response to hemoglobin, there was substantial variation in the expression of key biofilm dispersal markers, suggesting an underappreciated variation in biofilm regulome among S. aureus isolates and that no general inferences can be made by studying the behavior of single strains.

The Mechanism of Action of Ginkgolic Acid (15:1) against Gram-Positive Bacteria Involves Cross Talk with Iron Homeostasis

“…Iron was recently found to be associated with biofilm formation, antibiotic susceptibility, and pathogenicity in several bacterial species, although conclusions from multiple studies were highly inconsistent ( 32 , 37 – 40 ). In S. aureus , iron restriction enhances biofilm formation, and iron sourced from hemoglobin causes thicker and more structured biofilms than inorganic iron does ( 41 , 42 ). Mounting numbers of studies have focused on the antimicrobial activity of various antibiotics that were directly or indirectly linked to iron homeostasis.…”

Effect of Cobalt–Chromium–Molybdenum Implant Surface Modifications on Biofilm Development of S. aureus and S. epidermidis

“…S. aureus Newman has already been used for many studies on biofilm formation (e.g., Johnson et al, 2008 ; Abraham and Jefferson, 2012 ; Forson et al, 2020 ; Inés Molina et al, 2020 ; Pinto et al, 2020 ) although it is not considered a very good biofilm forming strain and the same is true for the ica negative S. epidermidis strain (e.g., Stepanovic et al, 2000 ; Lee et al, 2016 ; Paduszynska et al, 2019 ; Di Pilato et al, 2020 ; Paulitsch-Fuchs et al, 2021 ). However, the variant of the S. aureus strain used in this study S. aureus Newman D2C is considered to be a relatively good biofilm forming strain ( Grundmeier et al, 2004 ; Tsompanidou et al, 2010 ; Abraham and Jefferson, 2012 ; Dauros-Singorenko et al, 2020 ; Paulitsch-Fuchs et al, 2021 ). Abraham and Jefferson (2012) showed that the autolysin activity in the Newman D2C variant was low enough to allow the expression of ClfB on the cell surface, which seems to be (at least partly) responsible for the difference in biofilm forming abilities between the two strains.…”

“…and high iron contents did show a negative influence on agr expression in the hemoglobin study byDauros- Singorenko et al (2020), therefore possibly promoting biofilm formation of S. aureus Newman D2C in LB medium. This leads to another main influence on biofilm growth which is the medium used for the experiments.…”

Genetic Diversity in Staphylococcus aureus and Its Relation to Biofilm Production

“…S. aureus infections can be recurred and costs for a long-term treatment along with productivity losses [12]. This recurrence is the result of biofilm formation and persistence inside body.…”

“…In this way, biofilms can also act as source of spread for long term without being observed. Recent findings have shown that staphylococcal biofilm mechanisms are adaptable to the environmental changes and help the pathogen in adherence to the surfaces at any cost [12]. Genetic diversity could be one of the influencers among the biofilm production ability of this pathogen [16].…”