Interspecific Small Molecule Interactions between Clinical Isolates of Pseudomonas aeruginosa and Staphylococcus aureus from Adult Cystic Fibrosis Patients

Alexandre Fugère,André M Cantin,Gabriel Mitchell,Valérie Dekimpe,François Malouin,David Lalonde Séguin,Eric Frost,Eric Déziel,Michael Tunney

doi:10.1371/journal.pone.0086705

Abstract

Pseudomonas aeruginosa and Staphylococcus aureus are the most prevalent pathogens in airway infections of cystic fibrosis (CF) patients. We studied how these pathogens coexist and interact with each other. Clinical isolates of both species were retrieved from adult CF patients. Culture supernatants from 63 P. aeruginosa isolates triggered a wide range of biofilm-stimulatory activities when added to the culture of a control S. aureus strain. The extent of biofilm formation by S. aureus was positively correlated to the levels of the 2-alkyl-4-(1H)-quinolones (AQs) Pseudomonas Quinolone Signal (PQS) and 2-heptyl-4-hydroxy quinoline N-oxide (HQNO) produced by the P. aeruginosa isolates. Supernatants from P. aeruginosa isogenic mutants deficient in PQS and HQNO production stimulated significantly less biofilm formation by S. aureus than that seen with the parental strain PA14. When studying co-isolated pairs of P. aeruginosa and S. aureus retrieved from patients showing both pathogens, P. aeruginosa supernatants stimulated less biofilm production by the S. aureus counterparts compared to that observed using the control S. aureus strain. Accordingly, some P. aeruginosa isolates produced low levels of exoproducts and also some of the clinical S. aureus isolates were not stimulated by their co-isolates or by PA14 despite adequate production of HQNO. This suggests that colonization of the CF lungs promotes some type of strain selection, or that co-existence requires specific adaptations by either or both pathogens. Results provide insights on bacterial interactions in CF.

Highlights

Cystic fibrosis is a common life-shortening autosomal recessive disorder that manifests as clinical syndromes of chronic pulmonary infections, gastrointestinal disorder, nutritional and other abnormalities
To measure the effect of P. aeruginosa culture supernatants on S. aureus biofilm formation, the previously described clinical S. aureus strain CF1A-L [18], was used as a reference. This S. aureus strain was considered an adequate candidate to act as a control since it shows an increased biofilm production in response to P. aeruginosa PA14 supernatant and because it was originally retrieved from a cystic fibrosis (CF) patient who was not co-colonized with P. aeruginosa [18]
It was previously demonstrated that the P. aeruginosa exoproduct hydroxy quinoline N-oxide (HQNO) promotes the emergence of S. aureus small colony variants (SCVs) and importantly increases biofilm formation by prototypical S. aureus [16,18]

Summary

Introduction

Cystic fibrosis is a common life-shortening autosomal recessive disorder that manifests as clinical syndromes of chronic pulmonary infections, gastrointestinal disorder, nutritional and other abnormalities. The majority of individuals with CF succumb to respiratory failure primarily caused by chronic airway bacterial infections from mixed microbial communities [1]. S. aureus persists and is one of the most prevalent pathogens in adult CF patients along with P. aeruginosa [2,3,4]. Despite such documented and frequent co-colonization of S. aureus and P. aeruginosa, very little is known about the impact of polymicrobial infections on patient health. It has been proposed that S. aureus could prepare the respiratory tract epithelia of CF patients to promote the subsequent colonization of P. aeruginosa [13]. Studies are needed to understand how these microbial interactions develop, affect the balance of colonization and the progression of disease [14]

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