Microbiological study of biofilm formation in isolates of Salmonella enterica Typhimurium DT104 and DT104b cultured from the modern pork chain Denis O'Leary a, b, ⁎, Evonne M. Mc Cabe a, b , Matthew P. McCusker b , Marta Martins b , Séamus Fanning b , Geraldine Duffy a a Food Safety Department, Teagasc Food Research Centre, Ashtown, Dublin 15, Ireland b UCD School of Public Health, Physiotherapy and Population Science, UCD Centre for Food Safety, University College Dublin, Belfield, Dublin 4, Ireland abstract article info Article history: Received 4 July 2012 Received in revised form 30 October 2012 Accepted 27 November 2012 Available online 5 December 2012 Keywords: Biofilms Salmonella Typhimurium DT104 Phenotypic characterisation The purpose of this study was to characterise 172 Salmonella Typhimurium isolates taken from the pork chain for their biofilm forming abilities and to analyse their potential to survive on food processing surfaces. Many Salmonella have the ability to form biofilms. These natural structures, elaborated by bacteria are important in food production because their formation contributes to bacterial survival. Adherent bacterial cells are more resilient to displacement strategies including physical and chemical procedures as a consequence of their altered more resistant phenotype. By improving our understanding of the nature of biofilms, this data could positively contribute to the development and implementation of eradication strategies. In this study, Salmonella Typhimurium DT104 and DT104b were in- vestigated for their ability to form biofilms on a range of different surfaces under defined environmental growth conditions. Phenotypic characterisation involved examining colony morphology on indicator agars, assessing their ability to survive chlorine-based challenges and investigating their ability to attach to stainless steel and to plastic surfaces. All bacterial isolates were investigated for the presence of Salmonella genomic island I (SGI1) which is thought to enhance efficient biofilm formation. It was found that the majority of strains possess biofilm forming capabilities but successful attachment is highly dependent on the surface on which the biofilm is forming. The strains readily attached to stainless steel and plastic surfaces and survived high chlorine concentrations. Molec- ular and phenotypic comparisons of strong and weak biofilm forming strains indicate that biofilm development is not solely dependent on the acquirement of SGI1. © 2012 Elsevier B.V. All rights reserved. 1. Introduction Salmonella enterica serovar Typhimurium is a food-borne pathogen of importance to public health. This bacterium is a leading cause of gastroenteritis. S. Typhimurium DT104 is frequently isolated from pig abattoirs (Malorny et al., 2001; Perron et al., 2007) and from faecal samples from these animals (Zhang et al., 2005). The ability of S. Typhimurium to survive when challenged by antimicrobial com- pounds (Daly and Fanning, 2000; Molbak et al., 1999) and its ability to form multicellular structures called biofilms (Solano et al., 2002), contribute to its survival along the farm-to-fork continuum. A biofilm is composed of a community of interacting microorganisms attached to each other and to an exposed biotic or abiotic surface by a self-produced matrix (Costerton et al., 1995). This matrix consists of exopolysaccharides including cellulose and curli fimbriae, which are produced by the bacteria (Watnick and Kolter, 2000). Curli fimbriae are the main proteinaceous constituent of the bacte- rial biofilm matrix, and these structures contribute to cell aggregation and surface adhesion, leading to the formation of a mature biofilm (Austin et al., 1998). The formation of both cellulose and fimbriae fa- cilitates the development of a compact network of hydrophobic cells arranged in parallel in a robust matrix (Sutherland, 2001). This matrix provides a highly secure environment for all of the embedded cells while also facilitating the subsequent attachment to surfaces thereby ensuring a stable structural support (Sutherland, 2001). Exopolysaccharides present in the matrix also act as a physical barrier to external stressors, such as chlorine treatment often used as a sanitiser in many modern food production facilities (Solano et al., 2002; White et al., 2006). This matrix also confers high-level resis- tance to both antimicrobial agents, sanitisers (Assere et al., 2008; O'Toole et al., 2000), biocides (Finlay and Callow, 1997) and disinfec- tants (Gilbert et al., 2001) when compared to planktonically cultured bacterial cells. Planktonic or free-living bacterial cells begin the process of biofilm formation by attaching to an exposed surface (O'Toole et al., 2000) aided by weak electrostatic forces. This initial contact is then followed by bacterial growth and the assembly of an exopolysaccharide network that aid further attachment of bacteria to daughter cells and to the corre- sponding surfaces resulting in a three-dimensional (3D) type biofilm (Sutherland, 2001). Such structures have been shown to have distinctive International Journal of Food Microbiology 161 (2013) 36–43 ⁎ Corresponding author at: Food Safety Department, Teagasc Food Research Centre, Ashtown, Dublin 15, Ireland. Tel.: +353 1 8059986; Fax: +353 1 8059550. E-mail address: denis.oleary@teagasc.ie (D. O'Leary). 0168-1605/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.ijfoodmicro.2012.11.021 Contents lists available at SciVerse ScienceDirect International Journal of Food Microbiology journal homepage: www.elsevier.com/locate/ijfoodmicro