Pseudomonas aeruginosa is a frequently encountered pathogen that is involved in acute and chronic lung infections. Lectin-mediated bacterium-cell recognition and adhesion are critical steps in initiating P. aeruginosa pathogenesis. This study was designed to evaluate the contributions of LecA and LecB to the pathogenesis of P. aeruginosa-mediated acute lung injury. Using an in vitro model with A549 cells and an experimental in vivo murine model of acute lung injury, we compared the parental strain to lecA and lecB mutants. The effects of both LecA-and Lec B-specific lectin-inhibiting carbohydrates (␣-methyl-galactoside and ␣-methyl-fucoside, respectively) were evaluated. In vitro, the parental strain was associated with increased cytotoxicity and adhesion on A549 cells compared to the lecA and lecB mutants. In vivo, the P. aeruginosa-induced increase in alveolar barrier permeability was reduced with both mutants. The bacterial burden and dissemination were decreased for both mutants compared with the parental strain. Coadministration of specific lectin inhibitors markedly reduced lung injury and mortality. Our results demonstrate that there is a relationship between lectins and the pathogenicity of P. aeruginosa. Inhibition of the lectins by specific carbohydrates may provide new therapeutic perspectives.

IntroductionPseudomonas aeruginosa is a frequent cause of ventilator-acquired pneumonia (VAP). Candida tracheobronchial colonization is associated with higher rates of VAP related to P. aeruginosa. This study was designed to investigate whether prior short term Candida albicans airway colonization modulates the pathogenicity of P. aeruginosa in a murine model of pneumonia and to evaluate the effect of fungicidal drug caspofungin.MethodsBALB/c mice received a single or a combined intratracheal administration of C. albicans (1 × 105 CFU/mouse) and P. aeruginosa (1 × 107 CFU/mouse) at time 0 (T0) upon C. albicans colonization, and Day 2. To evaluate the effect of antifungal therapy, mice received caspofungin intraperitoneally daily, either from T0 or from Day 1 post-colonization. After sacrifice at Day 4, lungs were analyzed for histological scoring, measurement of endothelial injury, and quantification of live P. aeruginosa and C. albicans. Blood samples were cultured for dissemination.ResultsA significant decrease in lung endothelial permeability, the amount of P. aeruginosa, and bronchiole inflammation was observed in case of prior C. albicans colonization. Mortality rate and bacterial dissemination were unchanged by prior C. albicans colonization. Caspofungin treatment from T0 (not from Day 1) increased their levels of endothelial permeability and lung P. aeruginosa load similarly to mice receiving P. aeruginosa alone.ConclusionsP. aeruginosa-induced lung injury is reduced when preceded by short term C. albicans airway colonization. Antifungal drug caspofungin reverses that effect when used from T0 and not from Day 1.

Biofilms are prevalent in diseases caused by Pseudomonas aeruginosa, an opportunistic and nosocomial pathogen. By a proteomic approach, we previously identified a hypothetical protein of P. aeruginosa (coded by the gene pA3731) that was accumulated by biofilm cells. We report here that a ΔpA3731 mutant is highly biofilm-defective as compared with the wild-type strain. Using a mouse model of lung infection, we show that the mutation also induces a defect in bacterial growth during the acute phase of infection and an attenuation of the virulence. The pA3731 gene is found to control positively the ability to swarm and to produce extracellular rhamnolipids, and belongs to a cluster of 4 genes (pA3729–pA3732) not previously described in P. aeruginosa. Though the protein PA3731 has a predicted secondary structure similar to that of the Phage Shock Protein, some obvious differences are observed compared to already described psp systems, e.g., this unknown cluster is monocistronic and no homology is found between the other proteins constituting this locus and psp proteins. As E. coli PspA, the amount of the protein PA3731 is enlarged by an osmotic shock, however, not affected by a heat shock. We consequently named this locus bac for biofilm-associated cluster.

Transvascular transport of labeled-albumin is used to study endothelial permeability in experimental murine models of pulmonary infections. But radio-tagged albumin necessitates heavy safety procedures in terms of storage, manipulation and evacuation. The authors tested fluorescein isothiocyanate-tagged albumin (FITC-albumin) as a new marker for determination of endothelial permeability in a murine model of lung infection by Pseudomonas aeruginosa PAO1, in comparison with a standard method with (125)I-albumin. The mean permeability +/- SEM measured with (125)I-albumin was 2.45%/2 h +/- 0.37 for the control mice and 6.65%/2 h +/- 0.77 for the infected ones (P < .0001). With FITC-albumin, results obtained for both groups were respectively 4.96%/2 h +/- 0.64 and 11.5%/2 h +/- 1.2 (P < .0001). Spearman's rank coefficient was equal to .88 (P < .0001), showing a very strong correlation between both methods of measurement. The Bland-Altman analysis of bias revealed that there was no significant bias between FITC-albumin-derived and (125)I-albumin-derived values. The correction of the values obtained in plasma and lung homogenate supernatants by the subtraction of natural spontaneous fluorescence measured in these samples was crucial for the calculation of endothelial permeability in this new method. We believe that FITC-albumin can be useful for assessment of endothelial permeability in murine models of pulmonary diseases.