MEASURING DIAMETERS OF ROD-SHAPED BACTERIA IN-VIVO WITH POLARIZED-LIGHT SCATTERING

The angular function for elements of the Mueller matrix for polarized light scattering from suspensions of microorganisms is known to be rep roducible for different growths of a given bacterial strain in the log (or exponential) phase of growth. The reason for this, the stability of the size and shape distribution for cells, is briefly discussed. Ex periments were performed using suspensions of two different strains of Escherichia coli cells in log phase and measuring the angular depende nce of the Mueller matrix ratio S34/S11. Calculations were then perfor med using the coupled dipole approximation to model electromagnetic sc attering from particles where the shape of an individual cell was appr oximated by a cylinder capped with hemispheres of the same radius as t he cylinder. Using previously measured values for the length distribut ion and index of refraction of the cells, the calculated scattering cu rve was found to fit the measured curve very well. The values obtained for the cell diameters were quite close to diameters previously measu red by optical microscopy. Thus this method provides a rapid and conve nient method for monitoring bacterial diameters in vivo even when ther e is an appreciable distribution of bacterial lengths in the populatio n.