Impact of sub-inhibitory antibiotics on fibronectin-mediated host cell adhesion and invasion by Staphylococcus aureus

<p>Abstract</p> <p>Background</p> <p><it>Staphylococcus aureus </it>is a well-armed pathogen prevalent in severe infections such as endocarditis and osteomyelitis. Fibronectin-binding proteins A and B, encoded by <it>fnb</it>A/B, are major pathogenesis determinants in these infections through their involvement in <it>S. aureus </it>adhesion to and invasion of host cells. Sub-minimum inhibitory concentrations (sub-MICs) of antibiotics, frequently occurring <it>in vivo </it>because of impaired drug diffusion at the infection site, can alter <it>S. aureus </it>phenotype. We therefore investigated their impact on <it>S. aureus </it>fibronectin-mediated adhesiveness and invasiveness.</p> <p>Methods</p> <p>After <it>in vitro </it>challenge of <it>S. aureus </it>8325-4 and clinical isolates with sub-MICs of major anti-staphylococcal agents, we explored <it>fnb</it>A/B transcription levels, bacterial adhesiveness to immobilised human fibronectin and human osteoblasts in culture, and bacterial invasion of human osteoblasts.</p> <p>Results</p> <p>Oxacillin, moxifloxacin and linezolid led to the development of a hyper-adhesive phenotype in the fibronectin adhesion assay that was consistent with an increase in <it>fnb</it>A/B transcription. Conversely, rifampin treatment decreased fibronectin binding in all strains tested without affecting <it>fnb</it>A/B transcription. Gentamicin and vancomycin had no impact on fibronectin binding or <it>fnb</it>A/B transcription levels. Only oxacillin-treated <it>S. aureus </it>displayed a significantly increased adhesion to cultured osteoblasts, but its invasiveness did not differ from that of untreated controls.</p> <p>Conclusion</p> <p>Our findings demonstrate that several antibiotics at sub-MICs modulate fibronectin binding in <it>S. aureus </it>in a drug-specific fashion. However, hyper- and hypo- adhesive phenotypes observed in controlled <it>in vitro </it>conditions were not fully confirmed in whole cell infection assays. The relevance of adhesion modulation during <it>in vivo </it>infections is thus still uncertain and requires further investigations.</p

Crystal structures of 2,2′:6′,2″-terpyridine uranyl chlorides molecular assemblies and their luminescence signatures

International audienceA series of three compounds bearing uranyl cations and 2,2′:6′,2″-terpyridine (terpy) has been hydrothermally synthesized from uranium tetrachloride aqueous solution. An oxidation process into the hexavalent state has been observed for uranium in these synthesis conditions, together with the crystallization of different phases, which have been characterized by single-crystal X-ray diffraction analysis. The tetrachloridodioxidouranate terpyridinium salts UO2Cl4·H2terpy·H2O (1) and UO2Cl4·(H2terpy)2·2Cl (2) consist of the molecular assemblies of tetrachloro-uranyl anions ([UO2Cl4]2−, square plane bipyramidal environment), isolated to each other via the doubly protonated H2terpy molecules. The latter chelate either water (1) or chlorine anions (2). The addition of organic base such as pyridine favored the crystallization of the complex, UO2Cl2(terpy) (3), with the neutral terpy moiety coordinating one uranyl center via the nitrogen atoms of the pyridyl rings. It resulted in one uranyl center bonded to three nitrogen and two terminal chlorine anions, located in a distorted equatorial plane and two terminal perpendicular uranyl oxygens in apical position of a pentagonal bipyramid ([UO2Cl2N3]). Different π–π interactions between the pyridyl rings of neighboring terpy molecules also occur for these complexes. Fluorescence spectroscopy of these different complexes has been measured at room temperature and 77 K showing the various local environments of the emitting centers

Synthesis of α-oxosulfines by flash vacuum thermolysis of 2,3-dihydro-1,4-oxathin S-oxides. Photoelectron spectrum of thioxoethanal S-oxide.

International audienceRCOCR1SO (I; R = R1 = H, Me; R = Me, R1 = H) were generated by flash vacuum thermolysis of oxathiins. I (R = R1 = H) was characterized by low-temp. IR and, in particular, photoelectron spectroscopy. The exptl. IP's, as well as MNDO calcns., agree with the proposed structure [the (E)-s-cis conformation being the most stable] and exclude the formation of the cyclic isomers β-sulfine and 3-thia-1,2-dioxole. The Me derivs. were characterized by low-temp. IR and NMR spectroscopy, and chem. trapping by 2,3-dimethyl-1,3-butadiene. [on SciFinder(R)

PSMs of hypervirulent Staphylococcus aureus act as intracellular toxins that kill infected osteoblasts.

Epidemic community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA) is associated with more severe and acute forms of osteomyelitis than healthcare-associated (HA-) MRSA. Although S. aureus is now recognized as a facultative intracellular pathogen, the contribution of osteoblast invasion by CA-MRSA to the pathogenesis of osteomyelitis is unknown. Using an ex vivo model of intracellular infection of human osteoblasts, we demonstrated that CA-MRSA strains of diverse lineages share an enhanced ability to kill infected osteoblasts compared to HA-MRSA. Cytotoxicity comparisons of CA-MRSA isogenic deletion mutants revealed that phenol-soluble modulins (PSMs), a class of membrane-damaging exoproteins that are expressed at higher levels in CA-MRSA than in HA-MRSA, are involved in this osteoblast killing, whereas other major CA-MRSA virulence determinants, the Panton-Valentine leukocidin and alpha-toxin, are not involved. Similarly, functional agr and sarA regulators, which control the expression of PSMs and alpha-toxin, were required for the expression of the intracellular cytotoxic phenotype by CA-MRSA, whereas the saeRS regulator, which controls the expression of alpha-toxin but not PSMs, had no impact on cytotoxicity. Finally, PSM transcript levels determined by quantitative reverse-transcriptase PCR were significantly higher in CA-MRSA than in HA-MRSA strains and associated with cell damage in MRSA-infected osteoblasts. These findings provide new insights into the pathogenesis of severe CA-MRSA osteomyelitis and unravel a novel virulence strategy of CA-MRSA, based on the invasion and subsequent killing of osteoblasts by PSMs acting as intracellular toxins