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Surface imaging techniques were combined to determine appropriate manipulation of technologically important surfaces for commercial applications. The complementarity of the microscopy methods, scanning electron microscopy, electron probe microanalysis and atomic force microscopy assessed and correlated form and function of the surface modifications. Stainless steel disks (1 cm in diameter) were laser-cut from the same sheets of stainless steel and treated by electropolishing or left untreated for controls. Each treatment was analysed separately using each technique. First, the disks were examined by visual inspection and electron probe microanalysis for surface characteristics and elemental composition, respectively. Aliquots of bacterial suspensions (saline rinses of poultry carcasses from a commercial broiler processing plant) were then diluted in broth and monitored for growth by spectrophotometry. Stainless steel disks (1 cm in diameter) were added and the cultures were grown to sufficient density to allow attachment of bacterial cells to test surfaces. Relative differences in the surface morphology shown by atomic force microscopy, including Z ranges, roughness and other measurements, corresponded by treatment with the differences in reduction of bacterial counts shown by scanning electron microscopy. A model of wet-processing conditions tested the effects of corrosive treatment of surfaces. Less bacterial attachment occurred after corrosive treatment on controls and electropolished samples. Electropolishing significantly reduced bacterial numbers and the effects of corrosive action compared to the controls. Thus, the multiple imaging techniques showed that engineered changes on stainless steel surfaces improved the resistance of the surface finish to bacterial attachment, biofilm formation, and corrosive action.

Four bacteria, Bacillus cereus, B. subtilis, Escherichia coli, and Pseudomonas aeruginosa, were examined for the ability to remove Ag+, Cd2+, Cu2+, and La3+ from solution by batch equilibration methods. Cd and Cu sorption over the concentration range 0.001 to 1 mM was described by Freundlich isotherms. At 1 mM concentrations of both Cd2+ and Cu2+, P. aeruginosa and B. cereus were the most and least efficient at metal removal, respectively. Freundlich K constants indicated that E. coli was most efficient at Cd2+ removal and B. subtilis removed the most Cu2+. Removal of Ag+ from solution by bacteria was very efficient; an average of 89% of the total Ag+ was removed from the 1 mM solution, while only 12, 29, and 27% of the total Cd2+, Cu2+, and La3+, respectively, were sorbed from 1 mM solutions. Electron microscopy indicated that La3+ accumulated at the cell surface as needlelike, crystalline precipitates. Silver precipitated as discrete colloidal aggregates at the cell surface and occasionally in the cytoplasm. Neither Cd2+ nor Cu2+ provided enough electron scattering to identify the location of sorption. The affinity series for bacterial removal of these metals decreased in the order Ag greater than La greater than Cu greater than Cd. The results indicate that bacterial cells are capable of binding large quantities of different metals. Adsorption equations may be useful for describing bacterium-metal interactions with metals such as Cd and Cu; however, this approach may not be adequate when precipitation of metals occurs.