Fatima Hamadi

Effect of pH on distribution and adhesion of Staphylococcus aureus to glass

The adhesion of Staphylococcus aureus ATCC 25923 to glass at different pH values was investigated using scanning electron microscopy (SEM) and image analysis with the Mathlab® program. The images obtained by SEM show that the adhesion behaviour of Staphylococcus aureus ATCC 25923 depends on the pH of the suspending medium. At highly acidic (pH 2, pH 3) and alkaline pH, the cells deposited in aggregate forms, while at pH 5 the aggregation phenomenon was absent. The quantitative adhesion (number of adhering cells to glass surface) showed that cells adhered strongly in the pH range 4 to 6 and weakly at highly acidic (pH 2, pH 3) and alkaline pH. Moreover, the surface properties of the cells were characterized by the microbial adhesion to solvents (MATS) method. A good correlation was obtained between physicochemical properties (hydrophobicity or electron donor electron acceptor character) of Staphylococcus aureus ATCC 25923 and the number of adhering cells to glass. These results show that the adhesion of Staphylococcus aureus ATCC 25923 to glass is controlled by both acid–base and hydrophobic interactions.

Scanning Electron Microscopy (SEM) and Environmental SEM: Suitable Tools for Study of Adhesion Stage and Biofilm Formation

For most of the history of microbiology, microorganisms have primarily been characterized as planktonic, freely suspended cells and described on the basis of their growth characteristics in nutritionally rich culture media. The discovery of microorganisms, 1684, is usually ascribed to Antoni van Leeuwenhoek, who was the first person to publish microscopic observations of bacteria. The direct quantitative recovery techniques showed unequivocally that more than 99.9% of the bacteria grow in biofilms on a wide variety of surfaces. Although the most common mode of growth for microorganisms on earth is in surface associated communities (Stoodley et al., 2002; Sutherland, 2001), the first reported findings of microorganisms “attached in layers” were not made until the 1940s. During the 1960s and 70s the research on “microbial slimes” accelerated but the term “biofilm” was not unanimous formulated until 1984 (Bryers, 2000). Biofilm has three-dimensional (3D) structured, heterogeneous community of microbial cells enclosed in an exopolysaccharide matrix (also called glycocalyx) that are irreversibly attached to an inert or living surface. As establish, biofilm formation has a serious implications in public health and medicine. In the case of human health, a number of microbial infections are associated with surface colonization not only on live surfaces (sinusitis, pulmonary infection in cystic fibrosis patients, periodontitis, etc. (Hall-Stoodley et al., 2004) but also on medical implants (contact lenses, dental implants, intravascular catheters, urinary stents) etc. (Donlan, 2001; Hall-Stoodley et al., 2004). Biofilms affect heat exchangers, filters, etc. because they induce biocorrosion and biofouling, producing damages on metallic surfaces and the efficiency loss in industrial set-up (Dunne, 2002; Garret et al., 2008). However,biofilms have also useful applications in bioremediation (Vidali, 2001) of different environments (microorganisms degrade and convert pollutants into less toxic forms) and biolixiviation (bacteria can efficiently dissolve minerals used in industry, to obtain copper and gold).

Occurrence of Vibrio and Salmonella species in mussels ( Mytilus galloprovincialis ) collected along the Moroccan Atlantic coast

This study reports the occurrence of different Vibrio and Salmonella species in 52 samples of Mytilus galloprovincialis collected from four sites along the Atlantic coast between Agadir and Essaouira (Anza, Cap Ghir, Imssouane and Essaouira). The level of Escherichia coli (E. coli) was also determined to evaluate the degree of microbial pollution in the investigated areas. In this study three methods were used : AFNOR NF EN ISO 6579xa0V08-013 for Salmonella spp., the provisional method routinely used by several laboratories (Institut Pasteur, Paris,…) for Vibrio cholerae and Vibrio parahaemolyticus in the seafood, and the most probable number method (MPN) using Norm ISO/TS 16649–3 (2005) for E. coli. The most frequently isolated Vibrios were Vibrio alginolyticus (90.4% of samples), followed by V. cholerae non O1 non O139 (15.4%) and V. parahaemolyticus (7.7%). Salmonella spp. was found in 15% of the samples. The number of E. coli ranged between 0.2/100xa0g and 1.8 103 /100xa0g of mussel soft tissues. This study indicates the potential sanitary risk associated with the presence of pathogenic bacteria in cultivated mussels in the two populous regions of southern Morocco, where shellfish production and maritime tourism are important to the local economy.

Effect of temperature and plumbing materials on biofilm formation by Legionella pneumophila serogroup 1 and 2-15

Abstract The purpose of our study was to investigate the biofilm formation by Legionella pneumophila serogroup1 and serogroup2-15 on plumbing materials mostly used in building water systems in Morocco. The effect of plumbing materials and temperature were examined. The Atomic Force Microscopy was used to evaluate the roughness and surface topography of the plumbing materials including galvanized steel, stainless steel, copper, Polyvinyl chloride, Polypropylene Random Copolymer and Cross-linked polyethylene. Galvanized steel surfaces supported higher numbers of bacterial cells than that the stainless steel and plastic materials at 37 than 20 and 45 °C. Non-viable counts could be obtained from the copper surfaces. L. pneumophila sg2-15 strains presented a higher ability to biofilm formation than L. pneumophila sg1. The biofilm formation was evaluated by Atomic Force Microscopy.