Scattering pattern analysis of bacteria

Scattering pattern analysis for an ensemble of heterogeneous particles in a tenuous solution is applied to species identification and concentration estimation of bacteria with a view toward the development of a rapid automated technique to identify and count bacteria in urine. The scattering patterns measured with latex spheres and bacteria (Escherichia coli and Staphylococcus aureus) agree well with the theoretical calculations by the Mie theory and the Rayleigh-Debye approximation modified for size distributed and randomly oriented scatterers. The parameters (average size, axial ratio, size variation, refractive index) estimated in the scattering pattern analysis are reasonable. The sensitivity of the scattering pattern for the aggregation of scatterers is shown. Turbidimetry is improved by using the average total cross section calculated with the above parameters. The concentrations of above bacteria are estimated by this technique. They agree within a factor of 10 with the counts obtained by conventional plate count technique in a clinical microbiology laboratory. This error is acceptable for most practical applications of bacteria count in urine. Thus, the usefulness and effectiveness of the scattering pattern analysis in some of the practical applications are shown.