Functional Dissection of Streptococcus pyogenes M5 Protein: the Hypervariable Region is Essential for Virulence

The surface-localized M protein of Streptococcus pyogenes is a major virulence factor that inhibits phagocytosis, as determined ex vivo. Because little is known about the role of M protein in vivo we analyzed the contribution of different M protein regions to virulence, using the fibrinogen (Fg)-binding M5 protein and a mouse model of acute invasive infection. This model was suitable, because M5 is required for mouse virulence and binds mouse and human Fg equally well, as shown here. Mixed infection experiments with wild type bacteria demonstrated that mutants lacking the N-terminal hypervariable region (HVR) or the Fg-binding B-repeat region were strongly attenuated, while a mutant lacking the conserved C-repeats was only slightly attenuated. Because the HVR of M5 is not required for phagocytosis resistance, our data imply that this HVR plays a major but unknown role during acute infection. The B-repeat region is required for phagocytosis resistance and specifically binds Fg, suggesting that it promotes virulence by binding Fg. However, B-repeat mutants were attenuated even in Fg-deficient mice, implying that the B-repeats may have a second function, in addition to Fg-binding. These data demonstrate that two distinct M5 regions, including the HVR, are essential to virulence during the early stages of an infection. In particular, our data provide the first in vivo evidence that the HVR of an M protein plays a major role in virulence, focusing interest on the molecular role of this region

Identification of a plasminogen-binding motif in PAM, a bacterial surface protein.

Surface-associated plasmin(ogen) may contribute to the invasive properties of various cells. Analysis of plasmin(ogen)-binding surface proteins is therefore of interest. The N-terminal variable regions of M-like (ML) proteins from five different group A streptococcal serotypes (33, 41, 52, 53 and 56) exhibiting the plasminogen-binding phenotype were cloned and expressed in Escherichia coli. The recombinant proteins all bound plasminogen with high affinity. The binding involved the kringle domains of plasminogen and was blocked by a lysine analogue, 6-aminohexanoic acid, indicating that lysine residues in the M-like proteins participate in the interaction. Sequence analysis revealed that the proteins contain common 13-16-amino-acid tandem repeats, each with a single central lysine residue. Experiments with fusion proteins and a 30-amino-acid synthetic peptide demonstrated that these repeats harbour the major plasminogen-binding site in the ML53 protein, as well as a binding site for the tissue-type plasminogen activator. Replacement of the lysine in the first repeat with alanine reduced the plasminogen-binding capacity of the ML53 protein by 80%. The results precisely localize the binding domain in a plasminogen surface receptor, thereby providing a unique ligand for the analysis of interactions between kringles and proteins with internal kringle-binding determinants

Compliance with SSRI medication during 6 months of treatment for major depression: an evaluation by determination of repeated serum drug concentrations

Background: A recent estimation in a psychiatric cohort showed numbers of noncompliance between 10% and 60%. Therapeutic drug monitoring (TDM) is one method assessing compliance by analysis of drug concentration in the blood. Method: During a 24-week phase IV clinical trial, five repeated serum samples of sertraline (SERT) and N-desmethylsertraline (DSERT), trough values in steady state, were collected per patient. Previous results show that the intraindividual variation over time of the ratio DSERT/SERT is low. Hence, we hypothesized that significant partial noncompliance could be scrutinized further by an assessment of the DSERT/SERT ratio. The main aim was to test the applicability of a novel type of TDM procedure based on repeated metabolite/parent compound ratio measurements. Result: 9.4% of the per-protocol population in the trial (n = 96) were in either hidden total (n = 4) or hidden partial (n = 5) noncompliance. Only by using the novel TDM ratio screening method could a majority of these patients be identified

Serum disposition of sertraline, N-desmethylsertraline and paroxetine: A pharmacokinetic evaluation of repeated drug concentration measurements during 6 months of treatment for major depression

Sertraline and paroxetine are frequently prescribed SSRIs for long-term treatment of major depression. Nevertheless, continuous follow-ups of drug concentrations prevailing in patients during the whole treatment period are not available. Hence, in a large phase IV clinical trial, a total of 353 patients with major depression were enrolled for a 6-month comparison of sertraline (50-150 mg daily) and paroxetine (20-60 mg daily). The present study reports the pharmacokinetic results of up to eight serum samples per patient. 1. A profound variability was found in the interindividual steady state and trough serum levels of sertraline, desmethylsertraline and paroxetine: the coefficient of variation (CV) was 59% for sertraline, 51% for desmethylsertraline, 27% for the ratio desmethylsertraline/sertraline (50 mg/day), and 71% for paroxetine (20 mg/day). The intraindividual CV for the ratio desmethylsertraline/sertraline was only 19%, indicating intraindividual metabolizing stability over time. Both sertraline and paroxetine displayed sex differences in the dose-concentration correlation. 2. It was possible to predict sertraline, but not paroxetine, steady state levels. 3. The terminal elimination t1/2 for both drugs after 6 months of treatments was similar to data previously reported from short-term withdrawal studies. 4. No correlation between serum drug concentrations and clinical effect was detected for either sertraline or paroxetine. For the future, continuous efforts are warranted to perform PK investigations in the natural clinical setting in which the drugs are usually prescribed

Modulation of the Coagulation System During Severe Streptococcal Disease.

Haemostasis is maintained by a tightly regulated coagulation system that comprises platelets, procoagulant proteins, and anticoagulant proteins. During the local and systemic response to bacterial infection, the coagulation system becomes activated, and contributes to the pathophysiological response to infection. The significant human pathogen, Streptococcus pyogenes has multiple strategies to modulate coagulation. This can range from systemic activation of the intrinsic and extrinsic pathway of coagulation to local stimulation of fibrinolysis. Such diverse effects on this host system imply a finely tuned host-bacteria interaction. The molecular mechanisms that underlie this modulation of the coagulation system are discussed in this review