Antiserum agar method for identification of Smith type exopolysaccharides in clinical isolates of Staphylococcus aureus

RNAIII-inhibiting peptide improves efficacy of clinically used antibiotics in a murine model of staphylococcal sepsis

RNAIII-inhibiting peptide (RIP, YSPWTNF-NH2) is a quorum-sensing peptide inhibitor that prevents Staphylococcus aureus toxin production and biofilm formation. A mouse sepsis model was used to test the efficacy of RIP alone or in combination with conventional antibiotics in suppressing S. aureus-induced sepsis. Mice were injected intravenously with 3.0x10(6)CFU of S. aureus ATCC 25923 or with 3.0x10(6)CFU of S. aureus strain Smith diffuse. All animals were randomized to receive intravenously isotonic sodium chloride solution as a control, or 20 mg/kg RIP alone or combined with 20 mg/kg cefazolin, 10 mg/kg imipenem, or 10 mg/kg vancomycin immediately or 6 h after bacterial challenge. Main outcome measures were bacteremia and lethality. All compounds reduced lethality when compared to controls. Although, in general combined-treated groups had significant lower bacterial counts when associated to singly-treated groups only the combination between RIP and vancomycin with respect to cefazolin gave a statistically significant decrease in the lethality rate. Lowest lethality rates (10%) and bacteremia (<10(2)CFU/ml) were obtained when RIP was administered in combination with vancomycin. Because RIP can be synergistic with current antibiotic therapies and help to reduce S. aureus exotoxins production, it can be considered a promising agent to associate with antibiotics for further clinical research into treatment of sepsis.

Protection from lethal gram-positive infection by macrophage scavenger receptor-dependent phagocytosis

Infections with gram-positive bacteria are a major cause of morbidity and mortality in humans. Opsonin-dependent phagocytosis plays a major role in protection against and recovery from gram-positive infections. Inborn and acquired defects in opsonin generation and/or recognition by phagocytes are associated with an increased susceptibility to bacterial infections. In contrast, the physiological significance of opsonin-independent phagocytosis is unknown. Type I and II class A scavenger receptors (SR-AI/II) recognize a variety of polyanions including bacterial cell wall products such as lipopolysaccharide (LPS) and lipoteichoic acid (LTA), suggesting a role for SR-AI/II in innate immunity to bacterial infections. Here, we show that SR-AI/II-deficient mice (MSR-A(-/-)) are more susceptible to intraperitoneal infection with a prototypic gram-positive pathogen, Staphylococcus aureus, than MSR-A(+/+) control mice. MSR-A(-/-) mice display an impaired ability to clear bacteria from the site of infection despite normal killing of S. aureus by neutrophils and die as a result of disseminated infection. Opsonin-independent phagocytosis of gram-positive bacteria by MSR-A(-/-) macrophages is significantly decreased although their phagocytic machinery is intact. Peritoneal macrophages from control mice phagocytose a variety of gram-positive bacteria in an SR-AI/II-dependent manner. Our findings demonstrate that SR-AI/II mediate opsonin-independent phagocytosis of gram-positive bacteria, and provide the first evidence that opsonin-independent phagocytosis plays a critical role in host defense against bacterial infections in vivo.

The postantibiotic effect of N-chlorotaurine on Staphylococcus aureus. Application in the mouse peritonitis model

This study was designed to investigate the delay of regrowth (postantibiotic effect) in the presence of N-chlorotaurine (NCT), an endogenous active N-chlorine compound, of Staphylococcus aureus, strain Smith diffuse. The low reactivity of NCT enabled clear temporal separation of the postantibiotic and killing effect to be defined. Delay of regrowth proved to be dependent both on concentration of NCT, and incubation time. The maximum delay was 3 h. Using the model of lethal staphylococcal peritonitis in mice, in-vivo delay of regrowth of bacteria pretreated with N-chlorotaurine could be demonstrated to correlate with survival. It is concluded that the postantibiotic effect of N-chlorotaurine could be an important factor on decreasing virulence of bacteria. This effect was observed after relatively short incubation times.

Autoinducer of virulence as a target for vaccine and therapy against Staphylococcus aureus

Staphylococcus aureus causes pathologies ranging from minor skin infections to life-threatening diseases. Pathogenic effects are largely due to production of bacterial toxin, which is regulated by an RNA molecule, RNAIII. The S. aureus protein called RAP (RNAIII activating protein) activates RNAIII, and a peptide called RIP (RNAIII inhibiting peptide), produced by a nonpathogenic bacteria, inhibits RNAIII. Mice vaccinated with RAP or treated with purified or synthetic RIP were protected from S. aureus pathology. Thus, these two molecules may provide useful approaches for the prevention and treatment of diseases caused by S. aureus.