Streptococcus pyogenes organisms (group A streptococci) are considered to be highly adhesive extracellular pathogens. However, it has recently been reported that S. pyogenes has the capacity to efficiently invade eukaryotic cells. In this study, we demonstrate that the interaction of S. pyogenes fibronectin-binding protein (SfbI) with fibronectin on nonphagocytic HEp-2 cells triggers bacterial internalization. Blocking of the SfbI adhesin by either antibodies against the whole protein or antibodies against the fibronectin-binding domains of SfbI, as well as pretreatment of HEp-2 cells with purified SfbI protein, prevents both S. pyogenes attachment and internalization. Inert latex beads precoated with the purified SfbI protein are ingested by eukaryotic cells, demonstrating that SfbI is per se enough to trigger the internalization process. Experiments performed with a recombinant SfbI domain encompassing the two fibronectin-binding regions of the SfbI molecule demonstrated that these binding regions are essential and sufficient to activate uptake by HEp-2 cells. These results demonstrate that the fibronectin-binding protein SfbI is involved in both S. pyogenes' attachment to and ingestion by HEp-2 cells and contribute to elucidation of the underlying molecular events leading to eukaryotic cell invasion by S. pyogenes.

Streptococcal fibronectin binding protein I (SfbI) mediates adherence to and invasion of Streptococcus pyogenes into human epithelial cells. In this study, we analysed the binding activity of distinct domains of SfbI protein towards its ligand, the extracellular matrix component fibronectin, as well as the biological implication of the binding events during the infection process. By using purified recombinant SfbI derivatives as well as in vivo expressed SfbI domains on the surface of heterologous organism Streptococcus gordonii, we were able to dissociate the two major streptococcal target domains on the human fibronectin molecule. The SfbI repeat region exclusively bound to the 30 kDa N‐terminal fragment of fibronectin, whereas the SfbI spacer region exclusively bound to the 45 kDa collagen‐binding fragment of fibronectin. In the case of native surface‐expressed SfbI protein, an induced fit mode of bacteria–fibronectin interaction was identified. We demonstrate that binding of the 30 kDa fibronectin fragment to the repeat region of SfbI protein co‐operatively activates the adjacent SfbI spacer domain to bind the 45 kDa fibronectin fragment. The biological consequence arising from this novel mode of fibronectin targeting was analysed in eukaryotic cell invasion assays. The repeat region of SfbI protein is mediating adherence and constitutes a prerequisite for subsequent invasion, whereas the SfbI spacer domain efficiently triggers the invasion process of streptococci into the eukaryotic cell. Thus, we were able to dissect bacterial adhesion from invasion by manipulating one protein. SfbI protein therefore represents a highly evolved prokaryotic molecule that exploits the host factor fibronectin not only for extracellular targeting but also for its subsequent activation that leads to efficient cellular invasion.

We report here the discovery, isolation, and chemical and preliminary biological characterization of a new antibiotic compound, 7-O-malonyl macrolactin A (MMA), produced by a Bacillus subtilis soil isolate. MMA is a bacteriostatic antibiotic that inhibits a number of multidrug-resistant gram-positive bacterial pathogens, including methicillin-resistant Staphylococcus aureus, vancomycin-resistant enterococci, and a small-colony variant of Burkholderia cepacia. MMA-treated staphylococci and enterococci were pseudomulticellular and exhibited multiple asymmetric initiation points of septum formation, indicating that MMA may inhibit a cell division function.The spread of resistance to antibiotics undermines the therapeutic utility of anti-infective drugs in current clinical use (1). For example, Staphylococcus aureus, a major cause of community-and hospital-acquired infections, has developed resistance to most classes of antibiotics. Methicillin-resistant S. aureus (MRSA) strains appeared in the hospital environment after introduction of the semisynthetic penicillin methicillin, leaving vancomycin as the last line of defense for MRSA treatment (7). S. aureus organisms intermediately susceptible to vancomycin were first isolated in 1997 in Japan (15) and later in other countries (8). With the recent appearance of vancomycin-resistant clinical isolates (32,36,38), no antibiotic class is effective against multiresistant S. aureus infections. The increase in vancomycin-resistant enterococci (VRE), important agents of nosocomial infections, is another cause of great concern (2,3,19,27). Therapy options for multiresistant gramnegative opportunistic bacterial pathogens are also diminishing. Such bacteria, like Pseudomonas aeruginosa and Burkholderia cepacia (6), are common environmental organisms and opportunistic pathogens having the capacity to infect essentially all tissues of patients with compromised host defenses (21).Compounding the problem of genetically determined transmissible antibiotic resistance is the development of phenotypically resistant, often slow-growing, forms in chronic bacterial infections. These may take the form of biofilm microbes or small-colony variants (SCV) (12; reviewed in reference 14), are known to include both gram-positive and gram-negative pathogens, and are usually associated with a worsening of the disease prognosis.Thus, new antibiotics and therapy options are urgently needed to improve the management of bacterial infections (29, 35), and a major challenge is to find drugs that act against SCV and/or bacteria growing in biofilms.In this study, we report the discovery and preliminary characterization of 7-O-malonyl macrolactin A (MMA), a new antibiotic having bacteriostatic activity against clinical strains of MRSA, VRE, and a SCV of Burkholderia cepacia. The parental wild-type (WT) and SCV pairs of P. aeruginosa and B. cepacia, as well as Stenotrophomonas maltophilia strain 1124, were isolated from cystic fibrosis patients in the Department of Medical Microbiology at the Medical School...

The ability of three macrolide antibiotics (erythromycin, clarithromycin and azithromycin) to inhibit the expression of several pathogenicity traits of Pseudomonas aeruginosa at concentrations that do not affect the rate of growth of this microorganism was investigated. Sub-MICs of azithromycin manifested the broadest spectrum of action and strongly suppressed the synthesis of elastase, proteases, lecithinase and DNase. Clarithromycin and erythromycin were far less effective. Gelatinase was reduced almost to the same level by the three antibiotics, while haemolysins and lipase were only marginally affected. Loss of motility was a strain and drug-dependent event, but all the macrolides tested shared the ability to induce this effect. However, only azithromycin totally suppressed synthesis of pyocyanin in all isolates. These results indicate that newer macrolides and especially axithromycin are endowed with a remarkable ability to inhibit in vitro the expression of a number of physiological processes that are considered more essential than replication in the pathogenesis of P. aeruginosa. Since erythromycin sub-MICs have already been shown to exert beneficial effects in clinical practice, our data, pointing to a much higher potency of azithromycin, suggest its use in future studies.

Adherence to and invasion of epithelial cells represent important pathogenic mechanisms of Streptococcus pyogenes. A fibronectin‐binding surface protein of S. pyogenes, SfbI protein, has been implicated in both adherence and invasion processes. Invasion of SfbI‐containing strains has been suspected to be responsible for the failure of antibiotics treatment to eradicate S. pyogenes. In this study, we tested the adherence and invasion properties of two well‐characterized clinical isolates: A40, which expresses SfbI; and A8, which is SfbI negative and is unable to bind fibronectin. In strain A40, SfbI was the main factor required for attachment and invasion by using fibronectin as a bridging molecule and the α5β1 integrin as cellular receptor. The uptake process was characterized by the generation of large membrane invaginations at the bacteria–cell interface without evidence of actin recruitment or cellular injury. A40 cells were located in phagosomes and, only 24 h after infection, a consistent part of the bacterial population reached the cytoplasm. In contrast, uptake of strain A8 required major rearrangements of cytoskeletal proteins underneath attached bacteria. In A8, a proteinaceous moiety was involved, which does not interact with α5β1 or need any known bridging molecule. Bacterial attachment stimulated elongation and massive recruitment of neighbouring microvilli, which fused to surround streptococcal chains. They led to the generation of large pseudopod‐like structures, which engulfed bacteria that were rapidly released and replicated in the cytoplasm. The identification of two completely different uptake pathways reported here provided further evidence regarding the diversity of S. pyogenes isolates and might contribute towards understanding the pathogenesis and persistence of S. pyogenes.