The immune evasion roles of Staphylococcus aureus protein A and impact on vaccine development

While Staphylococcus aureus (S. aureus) bacteria are part of the human commensal flora, opportunistic invasion following breach of the epithelial layers can lead to a wide array of infection syndromes at both local and distant sites. Despite ubiquitous exposure from early infancy, the life-long risk of opportunistic infection is facilitated by a broad repertoire of S. aureus virulence proteins. These proteins play a key role in inhibiting development of a long-term protective immune response by mechanisms ranging from dysregulation of the complement cascade to the disruption of leukocyte migration. In this review we describe the recent progress made in dissecting S. aureus immune evasion, focusing on the role of the superantigen, staphylococcal protein A (SpA). Evasion of the normal human immune response drives the ability of S. aureus to cause infection, often recurrently, and is also thought to be a major hindrance in the development of effective vaccination strategies. Understanding the role of S. aureus virulence protein and determining methods overcoming or subverting these mechanisms could lead to much-needed breakthroughs in vaccine and monoclonal antibody development

A glycoconjugate of Haemophilus influenzae Type b capsular polysaccharide with tetanus toxoid protein: hydrodynamic properties mainly influenced by the carbohydrate

Three important physical properties which may affect the performance of glycoconjugate vaccines against serious disease are molar mass (molecular weight), heterogeneity (polydispersity), and conformational flexibility in solution. The dilute solution behaviour of native and activated capsular polyribosylribitol (PRP) polysaccharides extracted from Haemophilus influenzae type b (Hib), and the corresponding glycoconjugate made by conjugating this with the tetanus toxoid (TT) protein have been characterized and compared using a combination of sedimentation equilibrium and sedimentation velocity in the analytical ultracentrifuge with viscometry. The weight average molar mass of the activated material was considerably reduced (Mw ~ 0.24 × 106 g.mol−1) compared to the native (Mw ~ 1.2 × 106 g.mol−1). Conjugation with the TT protein yielded large polydisperse structures (of Mw ~ 7.4 × 106 g.mol−1), but which retained the high degree of flexibility of the native and activated polysaccharide, with frictional ratio, intrinsic viscosity, sedimentation conformation zoning behaviour and persistence length all commensurate with highly flexible coil behaviour and unlike the previously characterised tetanus toxoid protein (slightly extended and hydrodynamically compact structure with an aspect ratio of ~3). This non-protein like behaviour clearly indicates that it is the carbohydrate component which mainly influences the physical behaviour of the glycoconjugate in solution

Diffusion of meticillin-resistant Staphylococcus aureus USA300 strains in central Italy

Meticillin-resistant Staphylococcus aureus (MRSA) is an outstanding, clonally evolving pathogen that in recent years, under the selective pressure of antibiotics, has acquired the crucial ability to infect people outside of hospitals. MRSA USA300 has progressively become synonymous with severe community-associated staphylococcal disease worldwide. Whilst spreading worldwide, these clones have progressively acquired resistance to several antibiotics and have gained the ability to cause infections in hospital settings. Recently, USA300-related strains showing resistance to several antibiotics have been isolated from community-acquired infections in Italy. This paper reports the high frequency of isolation of USA300-related strains both from community- and hospital-acquired infections in central Italy as well as their genotypic characteristics and antibiotic susceptibility. Analysis of these characteristics by partial least squares discriminant analysis enabled it to be demonstrated that whilst moving from the community to the hospital setting these isolates underwent an adaptive process that generated clones showing distinctive characteristics. These observations further support the hypothesis that the threatening generation of strains combining both resistance and virulence is becoming a reality, and stress the necessity of constant molecular epidemiological surveillance of MRSA. (c) 2011 Elsevier B.V. and the International Society of Chemotherapy. All rights reserved

Diffusion of meticillin-resistant Staphylococcus aureus USA300 strains in central Italy

Meticillin-resistant Staphylococcus aureus (MRSA) is an outstanding, clonally evolving pathogen that in recent years, under the selective pressure of antibiotics, has acquired the crucial ability to infect people outside of hospitals. MRSA USA300 has progressively become synonymous with severe community-associated staphylococcal disease worldwide. Whilst spreading worldwide, these clones have progressively acquired resistance to several antibiotics and have gained the ability to cause infections in hospital settings. Recently, USA300-related strains showing resistance to several antibiotics have been isolated from community-acquired infections in Italy. This paper reports the high frequency of isolation of USA300-related strains both from community- and hospital-acquired infections in central Italy as well as their genotypic characteristics and antibiotic susceptibility. Analysis of these characteristics by partial least squares discriminant analysis enabled it to be demonstrated that whilst moving from the community to the hospital setting these isolates underwent an adaptive process that generated clones showing distinctive characteristics. These observations further support the hypothesis that the threatening generation of strains combining both resistance and virulence is becoming a reality, and stress the necessity of constant molecular epidemiological surveillance of MRSA. (c) 2011 Elsevier B.V. and the International Society of Chemotherapy. All rights reserved

Evaluation of the non-toxic mutant of the diphtheria toxin K51E/E148K as carrier protein for meningococcal vaccines

Diphtheria toxin mutant CRM197 is a common carrier protein for glycoconjugate vaccines, which has been proven an effective protein vector for, among others, meningococcal carbohydrates. The wide-range use of this protein in massive vaccine production requires constant increase of production yields and adaptability to an ever-growing market. Here we compare CRM197 with the alternative diphtheria non-toxic variant DT-K51E/E148K, an inactive mutant that can be produced in the periplasm of Escherichia coli. Biophysical characterization of DT-K51E/E148K suggested high similarity with CRM197, with main differences in their alpha-helical content, and a suitable purity for conjugation and vaccine preparation. Meningococcal serogroup A (MenA) glycoconjugates were synthesized using CRM197 and DT-K51E/E148K as carrier proteins, obtaining the same conjugation yields and comparable biophysical profiles. Mice were then immunized with these CRM197 and DT-K51E/E148K conjugates, and essentially identical immunogenic and protective effects were observed. Overall, our data indicate that DT-K51E/E148K is a readily produced protein that now allows the added flexibility of E. coli production in vaccine development and that can be effectively used as protein carrier for a meningococcal conjugate vaccine