The role of biofilm in the virulence and survival of Rhodococcus equi

THE ROLE OF BIOFILM IN THE VIRULENCE AND SURVIVAL OF RHODOCOCCUS EQUI E. Rampacci, PhD 1, M. L. Marenzoni, PhD 1, S. Giovagnoli, PhD 2,F. Passamonti, PhD 1, M. Coletti, DVM 1, D. Pietrella, PhD 2 1 Department of Veterinary Medicine, Perugia, Italia 2 Department of Pharmaceutical Sciences, Perugia, Italia Purpose of the work - Microbial biofilm research is crucial for combating chronic infectious diseases1. In spite of the fact that Rhodococcus equi is a recognized cause of chronic disease in foals and an emerging zoonotic agent threatening human health, few studies have been focused on the sessile phenotype of R. equi. The aim of this research was to provide evidence supporting the relevance of a putative biofilm-related process in R. equi disease and its answerability for hypo-responsiveness to azithromycin (AZM) and rifampicin (RIF) treatment. Materials and used methods - Fluorescence-based adhesion assay on pulmonary alveolar epithelium A549 ATCC® CCL-185 was performed to evaluate the ability of R. equi ATCC 33701 and 39 clinical isolates to adhere to the surface of lung epithelial cells, first necessary step for the formation of biofilm on the deep airway. Additionally, the extent of biofilm formation was measured by the kinetic microtiter biofilm formation assay. Further colorimetric experiments, fluorescence observations and scanning electron microscopy were carried out to examine the biofilm inhibition and dissolution power of AZM and RIF alone and combined in a 2:1 ratio. Results - Rhodococcus equi clearly has the capability to produce slow-growing biofilms, extending incubation beyond 24 h. Accordingly, all rhodococci adhered to lung alveolar epithelium in a concentration range considerably higher than the minimum in vivo infecting dose. Treating with AZM produced a higher long-term biofilm inhibition and dissolution than RIF, whose use should be considered as an adjunct treatment in place of monotherapy. The drug combination boosted the anti-biofilm effect in a statistically significant manner, although not equally effective for all isolates. No antimicrobial molecule, alone and in combination, was able to completely eradicate a pre-formed biofilm, whereas the RIF-resistant isolate produced an exceptionally abundant extracellular matrix. Conclusions - Biofilm production occurs as an antibiotic tolerance system in R. equi, potentially determining persistence of the chronic infection. Bibliography 1. Bjarnsholt T. The role of bacterial biofilms in chronic infections. APMIS Suppl. 2013;136:1-51. Corresponding Address: Dott.ssa Elisa Rampacci - Università degli Studi di Perugia, Via Sa