aureusstrains challenged with such antibiotic concentrations have been shown to exhibit altered phenotypes depending on the molecule tested, including down- or up-regulation of virulence factor expression. Conversely, rifampin treatment decreased fibronectin binding in all strains tested without affectingfnbA/B transcription. Gentamicin and vancomycin had no impact on fibronectin binding orfnbA/B transcription levels. Only oxacillin-treatedS. aureusdisplayed a significantly increased adhesion to cultured osteoblasts, but its invasiveness did not differ from that of untreated controls. == Conclusion == Our findings demonstrate that several antibiotics at sub-MICs modulate fibronectin binding inS. aureusin a drug-specific fashion. However, hyper- and hypo- adhesive phenotypes observed in controlledin GW1929 vitroconditions were not fully confirmed in whole cell infection assays. The relevance of adhesion modulation duringin vivoinfections is thus still uncertain and requires further investigations. == Background == Staphylococcus aureusis a prevalent and dangerous pathogen in humans, causing a wide range of infections. The initial step of suppurative infections, such as infective endocarditis or osteomyelitis, involves bacterial adhesion to the extracellular GW1929 matrix and cell surface of the host. Several microbial factors involved in this adherence are present inS. aureus[1]. Among these factors, collectively designated as microbial surface components recognising adhesive matrix molecules (MSCRAMMs), fibronectin-binding proteins A and B (FnBPA/B) play a major role inS. aureuspathogenicity through their ability to bind fibronectin and fibrinogen and to initiate integrin-mediated intracellular uptake of the bacteria by non-professional phagocytes such as endothelial cells or osteoblasts [2,3]. The invasion of host cells byS. aureuseventually leads to the formation of an intracytoplasmic reservoir, where bacteria remain protected from the action of cell- and antibody-mediated immune response and from that of most antimicrobial agents. This bacterial sanctuarisation makes successful treatment even more challenging and paves the way for infection relapse [4]. A peculiar difficulty to be faced in treating deep-seated infections is the risk of impaired diffusion of antimicrobial agents at the infection site, where they would only achieve sub-inhibitory concentrations.S. aureusstrains challenged with such antibiotic concentrations have been shown to exhibit altered phenotypes depending on the molecule tested, including down- or up-regulation GW1929 of virulence factor expression. For example, beta-lactams enhance the secretion of virulence factors such as the Panton-Valentine leukocidin and alpha haemolysin, while clindamycin or linezolid exert an inhibitory effect [5-8]. However, most studies on the antibiotic-mediated modulation of protein expression byS. aureushave focused on secreted exotoxins, and less is known about this modulation with respect to MSCRAMMS, including FnBPA/B. In the present study, we aimed to investigate the impact of sub-inhibitory concentrations of major anti-staphylococcal agents on the adhesion and invasion phenotypes ofS. aureus. GW1929 GW1929 Afterin vitrochallenge ofS. aureusreference strain 8325-4 and clinical isolates with antibiotics, we explored the following: (i) mRNA expression levels of thefnbA andfnbB genes, which encode FnBPA and B, respectively; (ii) Rabbit polyclonal to Fyn.Fyn a tyrosine kinase of the Src family.Implicated in the control of cell growth.Plays a role in the regulation of intracellular calcium levels.Required in brain development and mature brain function with important roles in the regulation of axon growth, axon guidance, and neurite extension. bacterial adhesiveness to immobilised human fibronectin and human osteoblasts in culture; and (iii) bacterial invasion of human osteoblasts. == Methods == == Bacterial strains == The bacterial strains used in this study are summarised in Table1. Laboratory strain 8325-4 and its fnbA/B derivative DU5883 were used as a control forfnbA/B [9]. Clinical isolates were characterised for the presence of thefnbA,fnbB,agr1-4 andmecA genes by PCR as previously described [10,11], and MLST was performed as described by Enright et al. to identify their genetic background [12]. == Table 1. == Characterisation of bacterial strains used in this study aSequence Type (ST) was determined as described by Enright et al. [12] == Antibiotics and MIC determination == The antibiotics used in this study were as follows: oxacillin, gentamicin, clindamycin, rifampicin and vancomycin purchased from Sigma-Aldrich (L’Isle d’Abeau, France); linezolid provided by Pfizer (Amboise, France); and moxifloxacin provided by Bayer (Wuppertal, Germany). Minimal inhibitory concentrations were determined by broth microdilution assay as recommended by the Clinical Laboratory Standards Institute (CLSI) standards [13]. == Bacterial cultures == The strains were cultured on trypticase blood agar plates and incubated overnight at 37C. Isolated colonies were resuspended in 5 ml brain heart infusion (BHI) in glass tubes (AES Chemunex France) and adjusted to 0.5 McFarland turbidity, corresponding to 108CFU/ml, as confirmed by bacterial count. Bacterial suspensions were cultivated at 37C with 300 rpm gyratory shaking. After 1 h, antibiotics.