Life Science Journal, 2011;8(4) http://www.lifesciencesite.com 37 Antimicrobial Activities of Gold Nanoparticles against Major Foodborne Pathogens M. F. Zawrah 1 and Sherein I. Abd El-Moez *2 1 Advanced Material & Nanotechnology Group, Center of Excellence for Advanced Sciences, National Research Center, Dokki, Cairo, Egypt 2 Department of Microbiology and Immunology, National Research Centre, Food Risk Analysis Group- Center of Excellence for Advanced Sciences Dokki, Cairo, Egypt. *shereinabdelmoez@yahoo.com Abstract: Spherical gold nanoparticles (Au) were chemically prepared and characterized by transmission electron microscope (TEM) and UV spectra. Their antimicrobial activities against major foodborne pathogens were studied. Antimicrobial activities of Au nanoparticles had been increased with their higher volume. Best antifungal activity was observed on using fluconazole coated with 40 μl Au nanoparticles with zone of inhibition 14mm against A. niger, 13mm C. albicans and 12mm A. flavus. Minimum inhibitory concentration test (MIC) revealed synergistic effect of Au nanoparticles with ciprofloxacin when compared with ciprofloxacin alone. Best results were shown against S. Typhimurium (0.097, 0.19), B. cereus (0.19, 0.39), E.coli O157 (0.39, 0.39), P. aeruginosa and L. monocytogenes (0.39, 0.78) and finally S. aureus (0.78, 6.25) respectively. Gold nanoparticles and fluconazole coated with Au nanoparticles showed variable MIC against C. albicans, A. niger (6.25, 3.125) and A. flavus (12.5, 6.25), respectively. TEM revealed small size of gold nanoparticles (range 9-19 nm) trapped by the biofilm released by S. Typhimurium and easily attached to the surface of cell membrane which drastically disturbed its proper function like respiration and permeability. Interaction between S. Typhimurium and ciprofloxacin coated with gold nanoparticles revealed that the cell wall was loosened and separated from the membrane or disrupted with complete absence of flagella. TEM of S. Typhimurium using ciprofloxacin alone showed intact bacterial cell wall with the accumulation of antibiotic on the cell wall and partial destruction of flagella. Drugs capped gold particle act as a single group against the microorganism which was indicated by using disk diffusion method with increase zone of inhibition of Au alone, ciprofloxacin alone and Au coated ciprofloxacin from 12, 26 and 30 mm, respectively. Also, it was clarified by the decrease in MIC from 6.25, 0.19 to 0.097, respectively. Results indicated that drugs coated with nanoparticles were highly effective against tested isolates so that Au nanoparticles can minimize treatment durations and side effects of drugs. [M. F. Zawrah and Sherein I. Abd El-Moez Antimicrobial Activities of Gold Nanoparticles against Major Foodborne Pathogens] Life Science Journal. 2011;8(4):37-44] (ISSN:1097-8135). http://www.lifesciencesite.com . Keywords: Antimicrobial, gold nanoparticles, foodborne pathogens, ciprofloxacin, S. Typhimurium, TEM. Introduction Nanotechnology offers unique approaches to control a wide variety of biological and medical processes that occur at nanometer length and it is believed to have a successful impact on biology and medicine (West and Halas 2000; Zandonella, 2003). By controlling the structure precisely at nano scale dimensions, one can control and modify their surface layer for enhanced aqueous solubility, biocompatibility or bio-conjugation. Nanoparticles exhibit attractive properties like high stability and the ability to modify their surface characteristics easily. The basic necessities for drug targeting are that the carrier should be capable of extended circulation in the blood stream; it must be small enough to gain access to target tissues and target cells (Tom et al. 2004). Nowadays, research efforts are being concentrated on integrating nanoparticles with biology. It has been reported that antibiotics often disturb the bacterial flora of digestive tract which may develop multiple drug-resistant isolates, hence novel ways of formulating biocide materials is an upcoming field of attraction (Jarvinen et al. 1993; Concannon et al. 2003; Altman et al. 2006; Daglia et al. 2007). For this reason, there is a need for the use of an agent which does not generate resistance and presents a good bactericidal property. Gold nanoparticles have a great bactericidal effect on a several range of microorganisms; its bactericidal effect depends on the size and the shape of the particle (Nirmala and Pandian, 2007). Nanoparticles can act as antibacterial and antifungal agents, due to their ability to interact with microorganisms (Hernandez et al. 2008; Dror- Ehre et al. 2009; Eby et al. 2009; Panacek et al. 2009). Exerting their antibacterial properties, nanoparticles attach to the surface of the cell. This interaction causes structural changes and damage, markedly disturbing vital cell functions, such as permeability, causing pits and gaps, depressing the activity of respiratory chain enzymes, and finally leading to cell death (Rai et al. 2009; Sharma et al. 2009; Li et al. 2010). In vitro antibacterial activities