Extent and Mode of Action of Cationic Legume Proteins against Listeria monocytogenes and Salmonella Enteritidis
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Extent and Mode of Action of Cationic Legume Proteins against Listeria monocytogenes and Salmonella Enteritidis Mahmoud Sitohy • Samir Mahgoub • Ali Osman • Ragab El-Masry • Aly Al-Gaby
Published online: 10 April 2013 Ó Springer Science+Business Media New York 2013
Abstract The methylated soybean protein and methylated chickpea protein (MSP and MCP) with isoelectric points around pI 8 were prepared by esterifying 83 % of their free carboxyl groups and tested for their interactions with Listeria monocytogenes and Salmonella Enteritidis. The two substances exhibited a concentration-dependent inhibitory action against the two studied bacteria with a minimum inhibitory concentration of about 100 lg/mL. The IC50 % of the two proteins against L. monocytogenes (17 lg/mL) was comparable to penicillin but comparatively much lower (15 lg/mL) than that of penicillin (85 lg/mL) against S. Enteritidis. The two proteins could inhibit the growth of L. monocytogenes and S. Enteritidis by about 97 and 91 %, respectively, after 6–12 h of incubation at 37 °C. The constituting subunits of MSP (methylated 11S and methylated 7S) were both responsible for its antimicrobial action. Transmission electron microscopy of the protein-treated bacteria showed various signs of cellular deformation. The cationic proteins can electrostatically and hydrophobically interact with cell wall and cell membrane, producing large pores, pore channels and cell wall and cell membrane disintegration, engendering higher cell permeability leading finally to cell emptiness, lysis and death. Keywords Antimicrobial Cationic proteins Listeria Salmonella Cell lysis M. Sitohy (&) A. Osman R. El-Masry A. Al-Gaby Biochemistry Department, Faculty of Agriculture, Zagazig University, Zagazig 44511, Egypt e-mail: [email protected] S. Mahgoub Microbiology Department, Faculty of Agriculture, Zagazig University, Zagazig 44511, Egypt
Introduction Listeria monocytogenes is an important food-borne pathogen causing listeriosis, a severe disease of high fatality rate in USA [1] and EU [2] where the incidence was 3 cases per million population in 2005. Capable of multiplication under high salt concentrations (10 % NaCl), broad pH range (pH 4.5–9) and different temperatures (0–45 °C), it can pose a potential risk to human health [3]. Salmonella spp. emerge in many foods by post-process recontamination, causing outbreaks of salmonellosis, another fatal food-borne disease. It can multiply to harmful levels during inappropriate storage conditions and can considerably grow at 8 °C [4]. An EC regulation on microbiological criteria for foodstuffs [5] was legislated and applied in force from January 2006, imposing the whole absence of Salmonella and a maximum permissible level of L. monocytogenes in foods of 100 CFU g-1 [5]. Resistance to antimicrobial agents by pathogenic bacteria has emerged in recent years, representing a major health problem [6], so the identification of new antimicrobial agents with different mechanisms of action is highly required. Cationic antimicro
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