Immunotherapeutic approaches against Staphylococcus aureus

Staphylococcus aureus is a major cause of life-threatening infections such as bacteremia and endocarditis. Unfortunately, many strains of this bacterial species have become resistant to certain antibiotics, including methicillin and amoxicillin. These strains are known as methicillin-resistant S. aureus (MRSA). Therefore, the prophylactic and therapeutic potential of antistaphylococcal vaccines is currently being explored with priority. In animal models, (passive) immunization with (antibodies directed against) certain S. aureus surface components, staphylococcal toxins and capsular polysaccharides protects against S. aureus colonization or infection. However, immunization studies performed in humans show less promising results. So far, not a single antistaphylococcal vaccine successfully passed clinical trials. This article focuses on the results that were obtained with immunotherapeutic approaches directed against S. aureus in animal and human studies. In addition, it is discussed whether effective immunization approaches against S. aureus are feasible in humans.     

Identification of in vivo-expressed antigens of Staphylococcus aureus and their use in vaccinations for protection against nasal carriage

A spectrum of in vivo-expressed Staphylococcus aureus antigens was identified by probing bacteriophage expression libraries of S. aureus with serum samples from infected and uninfected individuals. Eleven recombinant antigenic proteins were produced, and specific antibody titers in a large collection of human serum samples were determined. Significantly increased concentrations of reactive immunoglobulin G (IgG) to 7 antigens were found in serum samples from ill individuals, compared with those in healthy individuals. Significantly higher concentrations of reactive IgG to 4 antigens, including iron-responsive surface determinant (Isd) A and IsdH, were found in serum samples from healthy individuals who were not nasal carriers of S. aureus, compared with those in healthy carriers. Vaccination of cotton rats with IsdA or IsdH protected against nasal carriage. Also, IsdA is involved in adherence of S. aureus to human desquamated nasal epithelial cells and is required for nasal colonization in the cotton rat model. Thus, vaccination with these antigens may prevent S. aureus carriage and reduce the prevalence of human disease.     

How Staphylococcus aureus biofilms develop their characteristic structure

Biofilms cause significant problems in the environment and during the treatment of infections. However, the molecular mechanisms underlying biofilm formation are poorly understood. There is a particular lack of knowledge about biofilm maturation processes, such as biofilm structuring and detachment, which are deemed crucial for the maintenance of biofilm viability and the dissemination of cells from a biofilm. Here, we identify the phenol-soluble modulin (PSM) surfactant peptides as key biofilm structuring factors in the premier biofilm-forming pathogen Staphylococcus aureus. We provide evidence that all known PSM classes participate in structuring and detachment processes. Specifically, absence of PSMs in isogenic S. aureus psm deletion mutants led to strongly impaired formation of biofilm channels, abolishment of the characteristic waves of biofilm detachment and regrowth, and loss of control of biofilm expansion. In contrast, induced expression of psm loci in preformed biofilms promoted those processes. Furthermore, PSMs facilitated dissemination from an infected catheter in a mouse model of biofilm-associated infection. Moreover, formation of the biofilm structure was linked to strongly variable, quorum sensing-controlled PSM expression in biofilm microenvironments, whereas overall PSM production remained constant to ascertain biofilm homeostasis. Our study describes a mechanism of biofilm structuring in molecular detail, and the general principle (i.e., quorum-sensing controlled expression of surfactants) seems to be conserved in several bacteria, despite the divergence of the respective biofilm-structuring surfactants. These findings provide a deeper understanding of biofilm development processes, which represents an important basis for strategies to interfere with biofilm formation in the environment and human disease.     

Therapies against virulence products of Staphylococcus aureus and Pseudomonas aeruginosa

Methicillin-resistant STAPHYLOCOCCUS AUREUS (MRSA) and PSEUDOMONAS AERUGINOSA are key pathogens in hospitals (particularly intensive care units), in long-term care facilities, and in outpatients with specific comorbidities and risk factors. Both MRSA and P. AERUGINOSA display resistance to a wide array of antibiotics. Further, both bacteria contain a variety of virulence products or systems that make it difficult to treat associated infections. Within the past several years, community-acquired MRSA containing virulence factors [particularly the Panton-Valentine leukocidin (PVL) gene] has emerged globally. Given the limited number of novel antibiotics to treat antibiotic-resistant organisms, there is growing interest in treating bacterial infections by targeting specific virulence products or systems. This article reviews potential therapeutic targets in the virulence systems of these two bacteria that are responsible for a large number of serious infections in critically ill patients.     

Endotoxin-induced suppression of pulmonary antibacterial defenses against Staphylococcus aureus

In order to evaluate the effect of endotoxin on lung host defenses, Sprague-Dawley rats were intravenously injected with either placebo or 5 mg/kg of Escherichia coli lipopolysaccharide B. Two hours after treatment, animals were challenged with Staphylococcus aureus by either low dose aerosol inhalation or high dose intratracheal instillation of the bacteria into the lungs. Quantitative lung bacteriologic examination and bronchoalveolar lavage (BAL) for total and differential cell counts were performed immediately (zero hour) and at 4 h after bacterial challenge. Lung phagocytic defenses against aerosolized S. aureus challenges are provided solely by the alveolar macrophage (AM) in the absence of inflammation. In aerosol-challenged control rats, 20.6 +/- 2.0% of the initial deposited bacterial challenge remained viable in the lung at 4 h. Animals pretreated with endotoxin, however, showed a significant decrease in pulmonary bactericidal activity (31.3 +/- 3.4% bacteria remaining at 4 h), indicating a defect in alveolar macrophage (AM) function. Further assessment of the bactericidal oxidative metabolism of endotoxin-treated AM by luminol-enhanced chemiluminescence indicated an increased production of free radical oxygen species when compared with control nontreated cells in both the unstimulated (66 +/- 4 versus 38 +/- 7 x 10(3) cpm in control) and stimulated (250.5 +/- 17.1 versus 147.1 +/- 6.2 x 10(3) cpm in control) states. Total and differential cell counts in both control and endotoxin-treated aerosol-challenged rats were similar.(ABSTRACT TRUNCATED AT 250 WORDS)     

Bactericidal kinetics of 3 lactoferricins against Staphylococcus aureus and Escherichia coli

Bovine lactoferricin is an antimicrobial, cationic peptide generated upon gastric pepsin cleavage of bovine lactoferrin. We investigated the bactericidal effects of native lactoferricin [Lfcin B(17-41)], a shortened derivative [Lfcin B(17-31)] and the all-D-amino acid counterpart of Lfcin B(17-31) against Escherichia coli and Staphylococcus aureus. The results revealed different activities for the peptides against Gram-positive and -negative bacteria. D-Lfcin B(17-31) was the most efficient peptide against E. coli. The same peptide showed improved activity against S. aureus, D-Lfcin B(17-31) showed a significant better efficacy when compared to the L-form, but not when compared to Lfcin B(17-41). There was no correlation between the bactericidal concentrations and the time needed to achieve maximum effect. This indicates the importance of structural differences between the peptides and/or bacteria and implies that the simple thesis of I antibacterial target is not valid for lactoferricin.     

Comparison of bactericidal activity of five antibiotics against Staphylococcus aureus

Ten volunteers were given each of five antibiotics, sequentially, until steady state was reached. Peak and trough sera were then drawn, and bactericidal titers were determined to two different isolates of Staphylococcus aureus, both sensitive in vitro to all antibiotics tested. The antibiotics were cephalexin, trimethoprim/sulfamethoxazole (TMP/SMZ), clindamycin, dicloxacillin, and ciprofloxacin. Mean peak serum bactericidal titers (SBT) were significantly higher for cephalexin than for dicloxacillin, ciprofloxacin, and TMP/SMZ (P less than .05). The difference between cephalexin and clindamycin did not achieve statistical significance. Dicloxacillin, clindamycin, and ciprofloxacin were not statistically different from each other. Mean SBT for TMP/SMZ was less than 1:2, significantly less than that achieved by the other antibiotics. Only clindamycin achieved a trough SBT greater than 1:2. This was statistically significant compared with each of the other antibiotics.     

Novel synthesis of nanosilver particles using plant active principle aloin and evaluation of their cytotoxic effect against Staphylococcus aureus

ObjectiveTo develop a reliable, eco-friendly and easy process for the synthesis of silver nanoparticles using aloin, the active principle of medicinal plant ‘Aloe vera’ and to evaluate antimicrobial activity against Staphylococcus aureus (S. aureus), a causative organism of most of the diseases in livestock and to standardize the level of safety of synthesized silver nanoparticles.MethodsCharacterization using UV-vis spectrophotometry, DLS technique, FT-IR and SEM. Tube dilution method was carried out to evaluate the MIC of the compound against S. aureus. MTT assay was performed to evaluate the level of safety of nanoparticles.ResultsUV-vis absorption spectrum showed a maximum absorption around 200 nm for aloin mediated silver nanoparticles (ANS). The size of the particles as measured by DLS technique was 67.8 nm. The results of FT-IR analysis indicated the involvement of hydroxyl, carboxyl, amine and nitrile groups in the synthesis and stabilization of aloin mediated silver nanoparticles. SEM images showed that ANS with cubical, rectangular, triangular and spherical morphology and measured sizes of the agglomerated nanoparticles are in a range of 287.5 to 293.2 nm, however the average size of an individual particle is estimated to be approximately 70 nm. The compound (ANS) showed a MIC of 21.8 ng/mL against S. aureus and showed an in vitro spleenocyte viability of more than 80% at the highest concentration of 87.5 mg/L per well.ConclusionsAloin consists of functional groups which reduced Ag⁺ ions to Ag° ions and helped in synthesis of silver nanoparticles. The synthesis process has further enhanced the antimicrobial activity of nanosilver. The compound is also proved to be safe at the level many times higher than the MIC.     

Antimicrobial activity and synergism of Sami-Hyanglyun-Hwan with ciprofloxacin against methicillin-resistant Staphylococcus aureus

Objective: To investigate the antibacterial activity of SHHextracted with either water or ethanol against methicillin-resistant Staphylococcus aureus(MRSA) and combinatory antimicrobial effect with ciprofloxacin(CIP) by time kill assay and checkerboard dilution test. Methods: The antibacterial activity determined by broth dilution method indicated that the antibacterial activity of Sami-Hyanglyun-Hwan(SHH) water extract(SHHW) and SHH ethanol extract(SHHE) ranged from 250 to 2000 μg/m L and 125 to 1000 μg/m L against MRSA, respectively. Results: In the checkerboard method, the combinations of SHHE with CIP had a partial synergistic or synergistic effect against MRSA. The time-kill curves showed that a combined SHHE and CIP treatment reduced the bacterial counts dramatically after 24 h. Conclusions: The present study demonstrates the therapeutic ability of SHHE against MRSA infections.     

Effect of gentiana violet against methicillin-resistant Staphylococcus aureus (MRSA)]

The bactericidal effect of gentiana violet against MRSA isolated from clinical specimens was studied both in vitro and in vivo. The results obtained are as follows: 1) Minimum bactericidal concentration (MBC) of gentiana violet to MRSA was between 0.0025% and 0.08% and the MBC was not influenced even if 25% human whole serum exists in the medium. 2) The number of cells were 2.1 x 10(7) CFU/ml in medium which decreased to 5.4 x 10(4) CFU/ml within 5 min by existing 0.1% gentiana violet in the medium as the final concentration, and also decreased under 10(3) CFU/ml 15 min later. 3) Minimum inhibitory concentration (MIC) of gentiana violet to MRSA was between 0.00015% and 0.00063%, and the inhibitory activity was not influenced even if gentiana violet was incubated with the bacteria in the medium for 72 hr at 37 degrees C. 4) By using an ointment containing 0.1% gentiana violet to 12 cases of patients with the MRSA infected skin lesions, MRSA was eliminated completely from the infected areas of the skin within 4 weeks. 5) The side effects of gentiana violet were not observed in all cases during the use of the ointment containing gentiana violet. It is suggested that gentiana violet may be one of the useful drugs for the treatment of the skin lesions infected with MRSA.     

Diagnosing Staphylococcus aureus endocarditis by detecting antibodies against S. aureus capsular polysaccharide types 5 and 8

Consecutive serum samples from patients with Staphylococcus aureus endocarditis or septicemia or non-S. aureus endocarditis and febrile nonsepticemic controls were tested for antibodies against S. aureus capsular polysaccharide (CP) types 5 and 8 by ELISA. The upper normal antibody levels were defined as the upper 99.5% confidence limits of the values from the febrile controls. All available patient isolates were tested for the presence of CP type 5 or 8 (85% of the isolates expressed either serotype), and all five patients with S. aureus endocarditis had positive antibody levels against the corresponding serotype within the first 10 days of infection. Three other endocarditis patients lacked isolates for CP testing but two of these were positive. Positive antibody levels were found in 0 of 28 septicemia patients, in 1 of 12 non-S. aureus endocarditis patients, and in 3 of 37 febrile controls. Thus, testing for anti-CP 5 or 8 antibodies, especially together with CP serotyping of the patient's isolate, seems to provide important information in the differential diagnosis of endocarditis in patients with S. aureus septicemia.     

Host defenses against Staphylococcus aureus infection require recognition of bacterial lipoproteins

Toll-like receptors and other immune-signaling pathways play important roles as sensors of bacterial pattern molecules, such as peptidoglycan, lipoprotein, or teichoic acid, triggering innate host immune responses that prevent infection. Immune recognition of multiple bacterial products has been viewed as a safeguard against stealth infections; however, this hypothesis has never been tested for Staphylococcus aureus, a frequent human pathogen. By generating mutations that block the diacylglycerol modification of lipoprotein precursors, we show here that S. aureus variants lacking lipoproteins escape immune recognition and cause lethal infections with disseminated abscess formation, failing to elicit an adequate host response. Thus, lipoproteins appear to play distinct, nonredundant roles in pathogen recognition and host innate defense mechanisms against S. aureus infections.