African Journal of Microbiology Research Vol. 4 (11), pp. 1143-1147, 4 June, 2010 Available online http://www.academicjournals.org/ajmr ISSN 1996-0808 © 2010 Academic Journals Full length Research Paper Comparison of cell surface hydrophobicity and biofilm formation among ESBL-and non–ESBL-producing Pseudomonas aeruginosa clinical isolates Fatemeh Norouzi, Shahla Mansouri*, Mohammad Moradi and Mozhdeh Razavi Department of Microbiology, Medical School, Kerman University of Medical Sciences, P. O. Box 444, Kerman, Iran. Accepted 4 May, 2010 Pseudomonas aeruginosa is a major cause of nosocomial infections. Recently multidrug resistance and extended-spectrum ß-lactamase (ESBL)-producing P. aeruginosa isolates are emerging worldwide. These isolates are reported to be more virulent than the non multidrug resistance and non ESBL producing isolates. In order to find a correlation between ESBL production and virulence, we tested two cell surface factors involved in pathogenicity, hydrophobicity and biofilm formation in ESBL and non ESBL producing isolates. ESBL was determined phenotypically by combined disc method. Hydrophobicity was tested by microbial adhesion to hydrocarbon; biofilm formation was determined by microtiter plate. Mean of hydrophobicity in ESBL and non ESBL producing isolates was 38.85 and 30% respectively. Weak reaction in hydrophobicity was significantly higher in the non ESBL isolates (6%); while percent of moderate and strong reaction was higher in the ESBL producing isolates (94%). In biofilm formation mean of ESBL and non ESBL isolates were 0.182 and 0.136 respectively. Percent isolates producing moderate and strong biofilm was 72% for ESBL and 32% for non ESBL isolates (p value < 0.001). Our data demonstrate that hydrophobicity and biofilm formation was higher in the ESBL producing compared with non ESBL producing isolates. The properties can render the ESBL positive isolates more pathogenic. Key words: Pseudomonas aeruginosa, ESBL, hydrophobicity, biofilm formation, virulence. INTRODUCTION Pseudomonas aeruginosa is one of the most common pathogen causing nosocomial infections that affect mainly immunocompromised patients with severe underlying diseases (Cappello and Guglielmino, 2006). Infections cause by P. aeruginosa often are difficult to treat due to high level of resistance to multiple antibiotics as a result of both intrinsic and acquisition of resistance genes (Mesaros et al., 2007). In addition to constitutive low susceptibility of P. aeruginosa to antimicrobial agent emergence of new resistance mechanisms, such as ESBL belonging to different classes have been identified in these organisms. More studies found that antibiotic resistant phenotypic variants of P. aeruginosa have enhanced ability to form biofilm *Corresponding author. E-mail: smansouri@kmu.ac.ir. Tel: +989131423384. Fax: +983413221665. (Drenkard and Ausubel, 2002). Other studies demonstrate the relationship of PER-1-type ESBL- producing Acinetobacter spp. and P. aeruginosa with poor clinical outcome (Vahaboglu et al., 2001). ß- lactamases are mostly coded by plasmids and are transferable between different bacterial species; these enzymes confer resistance to penicillins, cephalosporins, and aztreonam (Philippon et al. 1994; Sturenburg and Mack, 2003). Infection caused by ESBL-producers are associated with severe adverse outcomes (Lee et al., 2006; Schwaber et al., 2006; Schwaber and Carmeli, 2007), infections caused by ESBL-producers may be related to increased virulence of these strains. Often due to delay in effective therapy and the failure to use antibiotic active against ESBL-producing isolates. Another possibility for the high rate of mortality considered with infections caused by ESBL-producers may be related to increased virulence of these strains. Indeed, several studies have reported an association