Rat Model Of Lung Infection Research Articles

Intravenous anti-MRSA phosphatiosomes mediate enhanced affinity to pulmonary surfactants for effective treatment of infectious pneumonia

The aim of this study was to develop PEGylated phosphatidylcholine (PC)-rich nanovesicles (phosphatiosomes) carrying ciprofloxacin (CIPX) for lung targeting to eradicate extracellular and intracellular methicillin-resistant Staphylococcus aureus (MRSA). Soyaethyl morphonium ethosulfate (SME) was intercalated in the nanovesicle surface with the dual goals of achieving strengthened bactericidal activity of CIPX-loaded phosphatiosomes and delivery to the lungs. The isothermal titration calorimetry (ITC) results proved the strong association of SME phosphatiosomes with pulmonary surfactant. We demonstrated a superior anti-MRSA activity of SME phosphatiosomes compared to plain phosphatiosomes and to free CIPX. A synergistic effect of CIPX and SME nanocarriers was found in the biofilm eradication. SME phosphatiosomes were readily engulfed by the macrophages, restricting the intracellular MRSA count by 1-2 log units. SME phosphatiosomes efficiently accumulated in the lungs after intravenous injection. In a rat model of lung infection, the MRSA burden in the lungs could be decreased by 8-fold after SME nanosystem application.

Pathogen identification by nuclear imaging – almost there?

Invasive fungal disease (IFD) in immunocompromised patients is a major infective cause of morbidity and mortality, with rates of death up to 90 % [1]. A key factor is the challenge of early diagnosis of IFD. In patients with haematological malignancy following intensive chemotherapy, immunosuppression and/or allogeneic haematopoietic stem cell transplantation, it is rarely possible to obtain the diagnostic material to definitively establish the presence of an IFD. The reasons for this are multiple, and include profound pancytopenia and poor performance status, which make tissue sampling of the lung (the main site for invasive aspergillosis, IA) hazardous. Equally, laboratory biological tests for IA have shown limited efficacy in the setting of blood sampling [2, 3], whereas bronchoalveolar lavage fluid appears to be a better material to assay, but bronchoscopy is an invasive intervention and may not be possible in an ill patient. All these factors, combined with post-mortem data showing higher rates of IFD than diagnosed ante-mortem [4], have led to empirical therapy as the standard of care in many centres around the world. The definition of empirical IFD therapy used throughout the literature is the commencement of treatment based on the clinical scenario alone, with the commonest situation being persistent neutropenic fever despite the use of broad-spectrum antibiotics. However, building on recent clinical studies [5–7], current management algorithms for IFD emphasize the importance of attempting to make a diagnosis, rather than relying on an empirical approach alone [8, 9]. CT scanning of the chest has a central role in the management of IA, with characteristic findings (nodules with or without a halo, consolidation with cavitation or an air crescent sign) supporting the diagnosis of IFD [10]. However, as the gold standard of a histological diagnosis or culture from sterile material is rarely possible, it becomes immediately obvious that even in a diagnosis-driven strategy combining imaging and galactomannan detection (the only widely used biomarker for IA), treatment is usually given without definitive proof of IA! Furthermore, while imaging of the chest with CT can support the diagnosis of IA, there are numerous alternative infections, as well as other disease processes; and galactomannan detection itself is associated with falsenegatives, false-positives and issues of reproducibility. The paper by Petrik et al. [11] offers hope of moving the field forward by combining imaging with pathogen detection. They have exploited the dependence on iron of many microorganisms, including Aspergillus fumigatus. In ironlimiting environments, A. fumigatus produces large amounts of siderophores, which are iron-chelating peptides that scavenge Fe and facilitate its uptake back into the organism [12]. Siderophores are essential for A. fumigatus virulence and deletions of genes involved in siderophore biosynthesis significantly impair fungal virulence [13]. Petrik et al. have taken advantage of the similarity of iron and gallium chemistry, already widely exploited in the use of Ga citrate, to label two siderophores with the short-lived, generatorproduced isotope Ga. They found that both compounds had good in vitro characteristics with respect to stability and specific uptake into A. fumigatus in culture as demonstrated by competition by either excess iron or unlabelled siderophore. Using small-animal PET/CT imaging in an immunocompromised rat model of lung infection with A. fumigatus, S. G. Agrawal Division of Haemato-Oncology, St Bartholomews Hospital and Blizard Institute, Queen Mary University of London, London EC1A 7BE, UK

Reconstitution of O-Specific Lipopolysaccharide Expression in Burkholderia cenocepacia Strain J2315, Which Is Associated with Transmissible Infections in Patients with Cystic Fibrosis

Burkholderia cenocepacia is an opportunistic bacterium that infects patients with cystic fibrosis. B. cenocepacia strains J2315, K56-2, C5424, and BC7 belong to the ET12 epidemic clone, which is transmissible among patients. We have previously shown that transposon mutants with insertions within the O antigen cluster of strain K56-2 are attenuated for survival in a rat model of lung infection. From the genomic DNA sequence of the O antigen-deficient strain J2315, we have identified an O antigen lipopolysaccharide (LPS) biosynthesis gene cluster that has an IS402 interrupting a predicted glycosyltransferase gene. A comparison with the other clonal isolates revealed that only strain K56-2, which produced O antigen and displayed serum resistance, lacked the insertion element inserted within the putative glycosyltransferase gene. We cloned the uninterrupted gene and additional flanking sequences from K56-2 and conjugated this plasmid into strains J2315, C5424, and BC7. All the exconjugants recovered the ability to form LPS O antigen. We also determined that the structure of the strain K56-2 O antigen repeat, which was absent from the LPS of strain J2315, consisted of a trisaccharide unit made of rhamnose and two N-acetylgalactosamine residues. The complexity of the gene organization of the K56-2 O antigen cluster was also investigated by reverse transcription-PCR, revealing several transcriptional units, one of which also contains genes involved in lipid A-core oligosaccharide biosynthesis.

Enhanced activity of liposomal polymyxin B against Pseudomonas aeruginosa in a rat model of lung infection

The bactericidal effectiveness of liposomal polymyxin B against Pseudomonas aeruginosa was investigated in an animal model of pulmonary infection. Polymyxin B was incorporated into liposomes composed of 1,2-dipalmitoyl- sn-glycero-3-phosphocholine (DPPC) and cholesterol (Chol) (2:1). Lung infection was induced in rats following intratracheal instillation of 10 7 colony-forming units (CFU) of P. aeruginosa (ATCC 27853) embedded in agar beads. Starting on day 3 post-infection, animals were treated daily, for 3 consecutive days, with saline, empty liposomes, free polymyxin B, or liposomal polymyxin B (2 mg polymyxin B/kg body weight) by intratracheal instillation; animals were killed 24 hr after the third drug instillation. Treatment of infected animals with liposomal polymyxin B significantly reduced the pulmonary bacterial counts (3.7±0.4 log CFU/paired lungs) as compared with that of free polymyxin B (5.1±0.2 log CFU/paired lungs). Treatment of infected animals with empty liposomes gave pulmonary bacterial counts similar to those obtained from the saline-treated group. Pulmonary infection with P. aeruginosa also resulted in lung injury as evidenced by increases in wet lung weight and decreases in angiotensin converting enzyme activity as well as increases in myeloperoxidase activity, an index of the inflammatory response. Treatment with free polymyxin B ameliorated the lung injuries induced by the microorganism, a protective effect that was more pronounced in the liposomal polymyxin B-treated group. The levels of polymyxin B in the lungs of the infected animals treated with the liposomal suspension were significantly higher (42.8±6.2 μg/paired lungs) compared with those treated with the free drug (8.2±0.4 μg/paired lungs). These data suggest that direct delivery of liposomal polymyxin B to the lung can be effective in the treatment of pulmonary infection with P. aeruginosa by enhancing retention of the antibiotic in the lung.