Biofilm formation and inflammatory potential of Staphylococcus saccharolyticus: A possible cause of orthopedic implant-associated infections

Mastaneh Afshar; Andreas Møllebjerg; Gabriel Antonio Minero; Jacqueline Hollensteiner; Anja Poehlein; Axel Himmelbach; Jeppe Lange; Rikke Louise Meyer; Holger Brüggemann

doi:10.3389/fmicb.2022.1070201

Biofilm formation and inflammatory potential of Staphylococcus saccharolyticus: A possible cause of orthopedic implant-associated infections

Front Microbiol. 2022 Nov 28:13:1070201. doi: 10.3389/fmicb.2022.1070201. eCollection 2022.

Authors

Affiliations

¹ Department of Biomedicine, Aarhus University, Aarhus, Denmark.
² Interdisciplinary Nanoscience Center (iNANO), Aarhus University, Aarhus, Denmark.
³ Department of Genomic and Applied Microbiology, Institute of Microbiology and Genetics, University of Göttingen, Göttingen, Germany.
⁴ Leibniz Institute of Plant Genetics and Crop Plant Research (IPK), Gatersleben, Germany.
⁵ Department of Clinical Medicine, Aarhus University, Aarhus, Denmark.
⁶ Department of Orthopedic Surgery Horsens Regional Hospital, Horsens, Denmark.
⁷ Department of Biology, Aarhus University, Aarhus, Denmark.

Abstract

Staphylococcus saccharolyticus, a coagulase-negative staphylococcal species, has some unusual characteristics for human-associated staphylococci, such as slow growth and its preference for anoxic culture conditions. This species is a relatively abundant member of the human skin microbiota, but its microbiological properties, as well as the pathogenic potential, have scarcely been investigated so far, despite being occasionally isolated from different types of infections including orthopedic implant-associated infections. Here, we investigated the growth and biofilm properties of clinical isolates of S. saccharolyticus and determined host cell responses. Growth assessments in anoxic and oxic conditions revealed strain-dependent outcomes, as some strains can also grow aerobically. All tested strains of S. saccharolyticus were able to form biofilm in a microtiter plate assay. Strain-dependent differences were determined by optical coherence tomography, revealing that medium supplementation with glucose and sodium chloride enhanced biofilm formation. Visualization of the biofilm by confocal laser scanning microscopy revealed the role of extracellular DNA in the biofilm structure. In addition to attached biofilms, S. saccharolyticus also formed bacterial aggregates at an early stage of growth. Transcriptome analysis of biofilm-grown versus planktonic cells revealed a set of upregulated genes in biofilm-embedded cells, including factors involved in adhesion, colonization, and competition such as epidermin, type I toxin-antitoxin system, and phenol-soluble modulins (beta and epsilon). To investigate consequences for the host after encountering S. saccharolyticus, cytokine profiling and host cell viability were assessed by infection experiments with differentiated THP-1 cells. The microorganism strongly triggered the secretion of the tested pro-inflammatory cyto- and chemokines IL-6, IL-8, and TNF-alpha, determined at 24 h post-infection. S. saccharolyticus was less cytotoxic than Staphylococcus aureus. Taken together, the results indicate that S. saccharolyticus has substantial pathogenic potential. Thus, it can be a potential cause of orthopedic implant-associated infections and other types of deep-seated infections.

Keywords: Staphylococcus saccharolyticus; anaerobes; biofilm; coagulase-negative staphylococci; implant-associated infection; inflammation; transcriptome.