DARK-FIELD MICROSCOPY ANALYSIS OF THE MAGNETIC DEPOSITION OF BACTERIAON A GLASS-SURFACE

Suspensions of bacteria, Escherichia coli, in 0.9% saline were treated by addition of a paramagnetic lanthanide salt, erbium chloride (ErCl3 ), and concentrated on a microscope slide using a magnetic field. The final concentration of Er3+ in solution was kept constant at 5 mM, and the concentration of bacteria, c, varied from 10(4) colony forming un its (CFU) ml-1 to 10(8) CFU ml-1. The magnetic deposition of bacterial cells on the microscopic slide was examined using dark-field microsco py. The sections of the magnetic deposition were scanned using the sca ttered light. The average intensity of the scattered light ASL was cor related with the initial concentration of bacterial cells in suspensio n, c. The data distribution was characterized by the regression line, log ASL = 0.3157 log c - 0.6388, number of slides N = 14, correlation coefficient R = 0.8881. The analysis of bacterial deposition from susp ension using a paramagnetic reagent, magnetic field and scattered-ligh t scanning may provide a quick means of testing for the presence of ba cteria in biological fluids or in environmental waters.