Pneumolysin potentiates oxidative inactivation of alpha-1-proteinase inhibitor by activated human neutrophils

Streptococcus pneumoniae: Invasion and Inflammation

Streptococcus pneumoniae (the pneumoccus) is the leading cause of otitis media, community-acquired pneumonia, and bacterial meningitis. The success of the pneumococcus stems from its ability to persist in the population as a commensal and avoid killing by immune system. This chapter first reviews the molecular mechanisms that allow the pneumococcus to colonize and spread from one anatomical site to the next. Then, it discusses the mechanisms of inflammation and cytotoxicity during emerging and classical pneumococcal infections.

Virulence factors in pneumococcal respiratory pathogenesis

Streptococcus pneumoniae (the pneumococcus) is a major global cause of human disease. Since the publication of the entire sequence of TIGR4 in 2001, our understanding of this human pathogen has increased significantly. Genetic studies, and the use of mutant strains have refined our understanding of the pathogenic mechanisms of classic pneumococcal virulence factors, including the polysaccharide capsule, pneumolysin and surface-expressed proteins. Genetic screens are identifying novel virulence factors. Characterization of pili and bacteriocins, as well as genes associated with competence, metabolism and resistance to oxidative stress has provided new insights into the genetic diversity of the pneumococcus. Further appreciation of the molecular basis of pneumococcal pathogenesis will lead to more effective strategies for the prevention and management of pneumococcal disease.

Controversies in the treatment of pneumococcal community-acquired pneumonia

Community-acquired pneumonia remains an important cause of disease and death both in the developed and the developing worlds, despite the ready availability of potent antimicrobial agents to which the organisms remain susceptible. Furthermore, disease management is complicated by emerging resistance of the common pathogens to the various classes of commonly prescribed antimicrobial agents. Much recent research in the field of community-acquired pneumonia has focused attention on optimal treatment, evaluating the impact of antibiotic resistance, as well as of antimicrobial choices, on the outcome of these infections. In addition, efforts have been directed towards finding adjunctive therapies to antibiotics that may improve the prognosis of these patients. This article reviews some of these research areas, highlighting controversies that still exist with regard to final recommendations, and in particular with regard to infections with Streptococcus pneumoniae, the most common bacterial cause of community-acquired pneumonia.

Safety and efficacy of recombinant alpha(1)-antitrypsin therapy in cystic fibrosis

Neutrophil elastase (NE) is thought to be the most important protease which damages the cystic fibrosis (CF) lung. Attempts have been made to suppress this activity using the plasma-derived inhibitor, alpha(1)-antitrypsin (AAT). In this pilot study, the safety and efficacy of inhaled recombinant human AAT (rAAT) as a treatment for CF were investigated. Thirty-nine patients participated in a prospective, double-blinded, randomized, placebo-controlled phase II trial to examine the effect of rAAT (500, 250, and 125 mg) on sputum NE activity. Sputum myeloperoxidase (MPO), interleukin-8, tumor necrosis factor receptors, sputum and plasma NE/AAT complexes, and safety parameters were also measured. Subjects were randomized to receive nebulized treatment once a day for 4 weeks, followed by 2-4 weeks with no study treatment, and then a 2-week rechallenge phase. Trends toward a reduction in NE activity were observed in patients treated with 500 mg and 250 mg of rAAT compared to placebo. Sputum NE/AAT complex and MPO levels were lower on rAAT compared to placebo. No major adverse events and, in particular, no allergic reactions to rAAT were observed. Although significant differences between rAAT and placebo for sputum NE activity were not observed, some improvements were found for secondary efficacy variables. This study demonstrated that nebulized rAAT is safe and well-tolerated, but has a limited effect on NE activity and other markers of inflammation.

Minimizing the release of proinflammatory and toxic bacterial products within the host: A promising approach to improve outcome in life-threatening infections

Various bacterial components (e.g., endotoxin, teichoic and lipoteichoic acids, peptidoglycans, DNA) induce or enhance inflammation by stimulating the innate immune system and/or are directly toxic in eukariotic cells (e.g., hemolysins). When antibiotics which inhibit bacterial protein synthesis kill bacteria, smaller quantities of proinflammatory or toxic compounds are released in vitro and in vivo than during killing of bacteria by beta-lactams and other cell-wall active drugs. In general, high antibiotic concentrations liberate lower quantities of bacterial proinflammatory or toxic compounds than concentrations close to the minimum inhibitory concentration. In animal models of Escherichia coli Pseudomonas aeruginosa and Staphylococcus aureus peritonitis/sepsis and of Streptococcus pneumoniae meningitis, a lower release of proinflammatory bacterial compounds was associated with a reduced mortality or neuronal injury. Pre-treatment with a bacterial protein synthesis inhibitor reduced the strong release of bacterial products usually observed during treatment with a beta-lactam antibiotic. Data available strongly encourage clinical trials comparing antibiotic regimens with different release of proinflammatory/toxic bacterial products. The benefit of the approach to reduce the liberation of bacterial products should be greatest in patients with a high bacterial load.