Downloaded from www.microbiologyresearch.org by IP: 54.70.40.11 On: Sat, 04 May 2019 21:03:12 Identity and effects of quorum-sensing inhibitors produced by Penicillium species Thomas Bovbjerg Rasmussen, 1 Mette E. Skindersoe, 1 Thomas Bjarnsholt, 1 Richard K. Phipps, 2 Kathrine Bisgaard Christensen, 2 Peter Ostrup Jensen, 3 Jens Bo Andersen, 1 Birgit Koch, 1 Thomas Ostenfeld Larsen, 2 Morten Hentzer, 4 Leo Eberl, 5 Niels Hoiby 3,6 and Michael Givskov 1 Correspondence Michael Givskov immg@pop.dtu.dk 1 Center for Biomedical Microbiology, BioCentrum-DTU, Technical University of Denmark, DK-2800 Kgs. Lyngby, Denmark 2 Center for Microbial Biotechnology, BioCentrum-DTU, Technical University of Denmark, DK-2800 Kgs. Lyngby, Denmark 3 Department of Clinical Microbiology, Rigshospitalet, DK-2100, Copenhagen Ø, Denmark 4 Carlsberg Research Center, Biosector, Gamle Carlsberg Vej 10, DK-2500 Valby, Denmark 5 Department of Microbiology, University of Zu ¨ rich, CH-8008 Zu ¨ rich, Switzerland 6 Department of Bacteriology, Institute of Medical Microbiology and Immunology, University of Copenhagen, Denmark Received 19 October 2004 Revised 21 January 2005 Accepted 25 January 2005 Quorum sensing (QS) communication systems are thought to afford bacteria with a mechanism to strategically cause disease. One example is Pseudomonas aeruginosa, which infects immunocompromised individuals such as cystic fibrosis patients. The authors have previously documented that blockage of the QS systems not only attenuates Ps. aeruginosa but also renders biofilms highly susceptible to treatment with conventional antibiotics. Filamentous fungi produce a battery of secondary metabolites, some of which are already in clinical use as antimicrobial drugs. Fungi coexist with bacteria but lack active immune systems, so instead rely on chemical defence mechanisms. It was speculated that some of these secondary metabolites could interfere with bacterial QS communication. During a screening of 100 extracts from 50 Penicillium species, 33 were found to produce QS inhibitory (QSI) compounds. In two cases, patulin and penicillic acid were identified as being biologically active QSI compounds. Their effect on QS-controlled gene expression in Ps. aeruginosa was verified by DNA microarray transcriptomics. Similar to previously investigated QSI compounds, patulin was found to enhance biofilm susceptibility to tobramycin treatment. Ps. aeruginosa has developed QS-dependent mechanisms that block development of the oxidative burst in PMN neutrophils. Accordingly, when the bacteria were treated with either patulin or penicillic acid, the neutrophils became activated. In a mouse pulmonary infection model, Ps. aeruginosa was more rapidly cleared from the mice that were treated with patulin compared with the placebo group. INTRODUCTION The 20th century initially offered the promising prospect of penicillin and other antibiotics to fight bacterial infections, but ended with the gloomy scenario of emerging multi- resistant bacteria. The efficiency of conventional antibiotics in preventing bacterial proliferation is the source of their success, but at the same time is also the cause of their failure. In many cases, selective pressure imposed by the use of conventional antibiotics leads to increased expression of degrading enzymes and development of drug-efflux sys- tems which operate with increased efficiency and therefore actively reduce the internal concentration of the anti- biotics. Furthermore, research over the last two decades has revealed that bacteria in the biofilm mode exhibit a higher tolerance to antimicrobial treatments (Anwar et al., 1990). The biofilm mode of growth also protects oppor- tunistic pathogens, such as Pseudomonas aeruginosa, against the action of the host immune system, which in turn facilitates establishment of chronic infections (Costerton et al., 1999). Abbreviations: AHL, N-acylated homoserine lactone; 123-DHR, dihydrorhodamine 123; GFP, green fluorescent protein; PMN, poly- morphonuclear leukocyte; QS, quorum sensing; QSI, QS inhibitor(y). 0002-7715 G 2005 SGM Printed in Great Britain 1325 Microbiology (2005), 151, 1325–1340 DOI 10.1099/mic.0.27715-0