Characterization of the virulence of Pseudomonas aeruginosa strains causing ventilator-associated pneumonia
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RESEARCH ARTICLE
Open Access
Characterization of the virulence of Pseudomonas aeruginosa strains causing ventilator-associated pneumonia Beatriz Alonso1,2* , Laia Fernández-Barat3,4, Enea Gino Di Domenico5, Mercedes Marín1, Emilia Cercenado1, Irene Merino6,7,8,9,10, Manuela de Pablos11, Patricia Muñoz1,2,12,13 and María Guembe1,2
Abstract Background: The objective of this study was to evaluate the virulence of P. aeruginosa ventilator-associated pneumonia (VAP) strains (cases) in terms of biofilm production and other phenotypic and genotypic virulence factors compared to P. aeruginosa strains isolated from other infections (controls). Methods: Biofilm production was tested to assess biomass production and metabolic activity using crystal violet binding assay and XTT assay, respectively. Pigment production (pyocyanin and pyoverdine) was evaluated using cetrimide agar. Virulence genes were detected by conventional multiplex PCR and virulence was tested in an in vivo model in Galleria mellonella larvae. Results: We did not find statistically significant differences between VAP and no-VAP strains (p > 0.05) regarding biofilm production. VAP strains had no production of pyocyanin after 24 h of incubation (p = 0.023). The distribution of virulence genes between both groups were similar (p > 0.05). VAP strains were less virulent than non-VAP strains in an in vivo model of G. mellonella (p < 0.001). Conclusion: The virulence of VAP-Pseudomonas aeruginosa does not depend on biofilm formation, production of pyoverdine or the presence of some virulence genes compared to P. aeruginosa isolated from non-invasive locations. However, VAP strains showed attenuated virulence compared to non-VAP strains in an in vivo model of G. mellonella. Keywords: Pseudomonas aeruginosa, Ventilator-associated pneumonia, Virulence genes, Biofilm, Galleria mellonella
Background Pseudomonas aeruginosa is one of the most common causes of ventilator-associated pneumonia (VAP), with high mortality rates (approximately 13%), prolonged hospital stays and increasing hospital costs [1]. VAP is a nosocomial lung infection that appears 48 h after intubation characterised by new lung infiltrates, signs of * Correspondence: [email protected] 1 Department of Clinical Microbiology and Infectious Diseases, Hospital General Universitario Gregorio Marañón, Madrid, Spain 2 Instituto de Investigación Sanitaria Gregorio Marañón, Madrid, Spain Full list of author information is available at the end of the article
systematic infection, changes in the appearance of sputum, leukocytosis and decline in oxygenation [2, 3]. The incidence of VAP ranges between 2 and 16 episodes per ventilator days being around 44% of the episodes caused by P. aeruginosa [4]. VAP is caused mainly by multidrug-resistant and extremely drug-resistant strains of P. aeruginosa, leading to an increase in treatment failure [5]. Moreover, the activity of antibiotics is restricted by P. aeruginosa biofilms that form rapidly on the surface of the endotracheal tube [6]. These microbial communities
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