ORIGINAL ARTICLE Effect of antibiotic-induced morphological changes on surface properties, motility and adhesion of nosocomial Pseudomonas aeruginosa strains under different physiological states A.P. Fonseca 1,2 and J.C. Sousa 3 1 Department of Microbiology, Faculty of Medicine, University of Porto, Porto, Portugal 2 IPATIMUP – Institute of Molecular Pathology and Immunology, University of Porto, Porto, Portugal 3 Department of Microbiology, Faculty of Health Sciences, University of Fernando Pessoa, Porto, Portugal Introduction Pseudomonas aeruginosa is an opportunistic human pathogen that colonizes biotic or abiotic surfaces and has emerged as an important source of nosocomial infections (Kipnis et al. 2006). Adhesion of planktonic cells is the initial step to form biofilms, which are responsible for more than 60% of the hospital-acquired infections (Ebrey et al. 2004). Biofilms are formed by a mixed population of rapidly and slow or nongrowing bacteria (Sufya et al. 2003; Roberts and Stewart 2005). These different physio- logical states may give protection, as slow-growing or sta- tionary phase cells have more tolerance to bactericidal antibiotics such as b-lactams that target macromolecular synthesis (Roberts and Stewart 2005); thus, biofilm resist- ance may be growth related (Spoering and Lewis 2001). At the site of infection, bacterial cells can be at different physiological states and several studies have been per- formed on the influence of growth phase on bacterial sur- face properties and adhesion abilities (Grasso et al. 1996; Keywords adhesion, antibiotics, morphology, motility, physiology, Pseudomonas aeruginosa, surface properties. Correspondence A.P. Fonseca, IPATIMUP, University of Porto, Rua Roberto Frias s ⁄ n, 4200 Porto, Portugal. E-mail: apfonseca05@sapo.pt 2006 ⁄ 1383: received 3 October 2006, revised 13 February 2007 and accepted 22 March 2007 doi:10.1111/j.1365-2672.2007.03422.x Abstract Aim: To investigate the influence of antibiotic-induced morphological changes on adhesion and motility abilities and surface properties of nosocomial Pseudo- monas aeruginosa under different physiological states. Methods and Results: The effects of subinhibitory concentration (sub-MIC) of Piperacillin ⁄ Tazobactam (P ⁄ T) and Imipenem (IMP) were studied on P. aeru- ginosa adhesion (1 h) using a modified microtitre-plate assay, on their ability to swim and to twitch, on surface hydrophobicity and on acid–base interac- tions of P. aeruginosa strains by measuring their ability to adhere to n-hexa- decane, chloroform and ethyl acetate, respectively. Our results show that antibiotic-induced morphological changes and bacterial physiological state can affect differently surface properties, motility and adhesion abilities of P. aerugi- nosa. Conclusions: Under different physiological states P ⁄ T induced morphological changes, reduced motility abilities, decreased adhesion to polystyrene and cell surface hydrophobicity (CSH). Moreover, P ⁄ T and IMP led to similar changes in exponential population adhesion to chloroform and ethyl acetate. Addition- ally, IMP induced morphological changes and showed no differences on CSH, adhesion and motility abilities in both growth phases. Significance and Impact of the Study: Adhesion is an attractive target for new antibacterial strategies, namely by using sub-MIC antibiotics that induce mor- phological, motility and surface properties changes, which are dependent of P. aeruginosa phenotype and physiological state. Journal of Applied Microbiology ISSN 1364-5072 1828 Journal compilation ª 2007 The Society for Applied Microbiology, Journal of Applied Microbiology 103 (2007) 1828–1837 ª 2007 The Authors