There has been a strong need for a rapid automated technique to count bacteria in urine. This paper demonstrates that the optical scattering pattern analysis for a collection of heterogeneous particles in a tenuous solution can be effectively applied to species identification and concentration estimation for bacteria. The scattering patterns are measured with latex spheres and bacteria (Escherichia coli and Staphylococcus aureus). They agree well with theoretical calculations using the Mie theory and the Rayleigh-Debye approximation, taking into account size distribution and random orientation. The parameters such as average size, axial ratio, size variation and refractive index are estimated to give a good agreement between the theory and the measurement. The values of the parameters agree with those in the literature. The scattering pattern is found to be sensitive to the aggregation of scatterers. The parameters obtained from the scattering pattern analysis are used to improve the estimation of bacterial concentrations by turbidimetry. The estimated values agree within a factor of 10 with those obtained by conventional culturing technique.