Attachment and Biofilm Formation by Salmonella in Food Processing Environments

Abstract

During the last decades, it has become increasingly clear that bacteria, including foodborne pathogens such as Salmonella enterica, grow predominantly as biofilms in most of their natural habitats, rather than in planktonic mode. A biofilm can be broadly defined as a microbially derived sessile community characterized by cells that are irreversibly attached to a substratum or interface or to each other, are embedded in a matrix of extracellular polymeric substances (EPS) that they have produced, and exhibit an altered phenotype with respect to growth rate and gene transcription (Donlan & Costerton, 2002; Kuchma & O’Toole, 2000; Lazazzera, 2005; Shemesh et al., 2007). Interestingly, it has been observed that the resistance of biofilm cells to antimicrobials is significantly increased compared with what is normally seen with the same cells being planktonic (Gilbert et al., 2002; Mah & O’Toole, 2001). Thus, it is believed that biofilm formation enhances the capacity of pathogenic Salmonella bacteria to survive stresses that are commonly encountered both within food processing, as well as during host infection. In food industry, biofilms may create a persistent source of product contamination, leading to serious hygienic problems and also economic losses due to food spoilage (Brooks & Flint, 2008; Carpentier & Cerf, 1993; Ganesh Kumar & Anand, 1998; Lindsay & von Holy, 2006; Zottola & Sasahara, 1994). Improperly cleaned surfaces promote soil build-up, and, in the presence of water, contribute to the development of bacterial biofilms which may contain pathogenic microorganisms, such as Salmonella. Cross contamination occurs when cells detach from biofilm structure once food passes over contaminated surfaces or through aerosols originating from contaminated equipment. Till now, there is only limited information on the presence of Salmonella in biofilms in real food processing environments. However, numerous studies have shown that Salmonella can easily attach to various food-contact surfaces (such as stainless steel, plastic and cement) and form biofilms under laboratory conditions (Chia et al., 2009; Giaouris et al., 2005; Giaouris & Nychas, 2006; Hood & Zottola, 1997a,b; Marin et al., 2009; Oliveira et al., 2006; Rodrigues et al., 2011; Vestby et al., 2009a,b). The natural environments that most bacteria inhabit are typically complex and dynamic. Unfortunately, this complexity is not fully appreciated when growing microorganisms in monocultures under laboratory conditions. Thus, in real environments, biofilm communities