ORIGINAL PAPERS Biofilm production, adherence and morphological alterations of Shigella spp. under salt conditions Ali Ellafi & Fethi Ben Abdallah & Rihab Lagha & Besma Harbi & Amina Bakhrouf Received: 24 June 2010 / Accepted: 21 December 2010 / Published online: 13 January 2011 # Springer-Verlag and the University of Milan 2011 Abstract In this study, we investigated the survival, adhesion and the morphology of Shigella after its incubation in various concentrations of salts. Our results showed that, after 48 h of incubation, the rate of cell survival is inversely proportional to the increase of salinity of the medium. In addition to that, the results prove the evidence that the concentration of salt can significantly influence the capacity of Shigella to produce biofilm on Congo red agar and on polystyrene microplate wells. Adherence and invasion assays of Shigella were performed with KB cells line. Indeed, an increase of the salts concentration enhances the ability of Shigella species to attach and to invade the tissue culture cells. The percentage of adherence was increased to 15% and the invasion to 90% at 6% of salt. The atomic force micrographs showed a reduction of the cells’ size after stress. Keywords Shigella . Salt . Survival . Adhesion . Invasion . Morphology Introduction Shigella spp. is a Gram-negative enteric bacterium which causes bacillary dysentery in human beings, accounting for 20% of the 4.6 million diarrhea-associated deaths among children (Ahmed et al. 2001). Shigella was the third most prevalent foodborne pathogen reported in 2004 by the Foodborne Diseases Active Surveillance Network (Food- Net) of the US Centers for Disease Control and Preven- tion's (CDC) Emerging Infections Program, accounting for 2,231 of the 15,806 total laboratory-diagnosed cases of infections (Centers for Disease Control and Prevention 2005). Food-processing methods have been developed to interfere with bacterial homeostasis, prevent growth, or kill foodborne pathogens (Abee and Wouters 1999). Some common hurdles used to control microbial growth are pH, sodium chloride, and storage temperature. Consumer demand for high-quality fresh or minimally processed products has resulted in many foods using a combination of acid, salt, and cold storage to prevent microbial growth. Several studies show that changes in temperature and osmolarity have a strong influence on the ability of these pathogens to be the cause of many diseases (Maurelli et al. 1984; Bernardini et al. 1990). Indeed, the characteristics of the suspending medium, such as pH, osmolarity and temperature, are considered to be important factors in altering the physicochemical properties of a bacterial surface (Hamadi et al. 2004). Generally, bacteria have a natural tendency to adhere to surfaces as a survival mechanism and bacterial colonization of solid surfaces has been described as a basic and natural bacterial stratagem in a wide variety of environments (Hunt et al. 2004). The initial step in the colonization is a thermodynamic process mediated by non-specific physicochemical interactions (Donlan and Costerton 2002) which depend on nutrient availability and physical stress caused by environmental factors, growth and nutritional status of the bacterial population. Hydrophobicity of the bacterial cell surface (CSH) is one of the most important factors which govern the mechanism of bacterial adhesion to inanimate and biological surfaces (Vesterlund et al. 2005). Lewis (2001) shows that Shigella can be tolerate antimicrobial agents, and can also be extraordinarily resistant to phagocytosis, making biofilms extremely difficult to eradicate from living hosts. A. Ellafi (*) : F. B. Abdallah : R. Lagha : B. Harbi : A. Bakhrouf Laboratory of Analysis, Treatment and Valorization of Environment Polluants and Product, Faculty of Pharmacy, Monastir, Tunisia e-mail: ali_lafi160@yahoo.fr Ann Microbiol (2011) 61:741–747 DOI 10.1007/s13213-010-0190-5