Short Communication

hoWorld J Microbiol Biotechnol (2009) 25:527–531 DOI 10.1007/s11274-008-9919-8

SHORT COMMUNICATION

A study on the effects of some laboratory-derived genetic mutations on biofilm formation by Listeria monocytogenes
Sanath Kumar Æ Ammini Parvathi Æ Jeffy George Æ Georg Krohne Æ Indrani Karunasagar Æ Iddya Karunasagar

Received: 25 July 2008 / Accepted: 11 November 2008 / Published online:28 November 2008 Ó Springer Science+Business Media B.V. 2008

Abstract Biofilms formed by the human pathogen Listeria monocytogenes in food-processing environments can be a potential source of contamination. In this study, we investigated the ability of L. monocytogenes wild type and its laboratory-derived isogenic mutants in cwhA, prfA, agrA, flaA, degU, ami and sigB to adhere to and form biofilmson abiotic surfaces. The results suggest that inactivation of the two component regulatory system degU completely abolished biofilm formation, while inactivation of the flagellar gene flaA, two component response regulator agrA and the autolysin-adhesin gene ami lead to severe impairment of initial attachment and the subsequent development of a mature biofilm by L. monocytogenes. Mutants in the globalregulator of virulence prfA and the alternative sigma factor sigB were unaffected and formed biofilms similar to wild type L. monocytogenes. Keywords Listeria monocytogenes Á Biofilm Á ami Á agrA Á Electron microscopy

Introduction Listeria monocytogenes is a gram-positive facultative intracellular pathogen capable of causing fatal infections in susceptible populations. These infections are morecommon in the newborn, pregnant women and immunocompromised individuals, with symptoms such as meningitis, encephalitis and septicaemia. L. monocytogenes has been associated with several outbreaks involving ready-to-eat food products (Lianou and Sofos 2007). The fatality rate associated with L. monocytogenes infections is as high as 30%, making it one of the most important food-borne pathogens.The organism is widely distributed in the environment, with the ability to survive adverse conditions. Many bacteria have the ability to attach to abiotic surfaces and form sessile communities known as biofilms (Davey and O’Toole 2000). Biofilms consist of bacteria embedded in an extra-cellular polymeric substance, and the biofilm bacteria are resistant to antimicrobials such as plant disinfectants, UVlight and drying. Biofilm formation in the food-processing environment by pathogenic bacteria is of great concern, since such bacteria can contribute to postprocess contamination. Several studies have shown that Listeria is widely present in the processing environs. In many studies, contamination of finished products with L. monocytogenes has been attributed to the presence of this organism infood-processing equipment. Though the studies indicate that L. monocytogenes is capable of forming biofilms, strain-to-strain variations have been observed (Djordjevic et al. 2002; Borucki et al. 2003). Recent studies have described the roles of alternative sigma factor sigma B (rB), flagellin, LuxS, DegU and the Agr systems of L. monocytogenes in surface attachment and biofilm formation (Vatanyoopaisarnet al. 2000; Schwab et al. 2005; Sela et al. 2006; Tresse et al. 2006; Rieu et al. 2007). In the

S. Kumar Á J. George Á I. Karunasagar Á I. Karunasagar Department of Fishery Microbiology, College of Fisheries, Karnataka Veterinary, Animal and Fisheries Sciences University, Mangalore 575 002, India A. Parvathi Molecular Biology Laboratory, Department of Biological Oceanography, NationalInstitute of Oceanography (CSIR), Kochi 682 018, India G. Krohne Division of Electron Microscopy, Biocenter of the University of Wurzburg, Am Hubland, 97074 Wurzburg, Germany S. Kumar (&) ENMU 2386, 1500 S, Ave. K, Portales, NM 88130, USA e-mail: sanathkm@yahoo.com

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World J Microbiol Biotechnol (2009) 25:527–531

study described here, we compared the biofilms formed by wild type (WT)...