The identification of bacterial pathogens from culture is critical to the proper administration of antibiotics and patient treatment. Many of the tests currently used in the clinical microbiology laboratory for bacterial identification today can be highly sensitive and specific; however, they have the additional burdens of complexity, cost, and the need for specialized reagents. We present an innovative, reagent-free method for the identification of pathogens from culture. A clinical study has been initiated to evaluate the sensitivity and specificity of this approach. Multiwavelength transmission spectra were generated from a set of clinical isolates including Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa, and Staphylococcus aureus. Spectra of an initial training set of these target organisms were used to create identification models representing the spectral variability of each species using multivariate statistical techniques. Next, the spectra of the blinded isolates of targeted species were identified using the model achieving >94% sensitivity and >98% specificity, with 100% accuracy for P. aeruginosa and S. aureus. The results from this on-going clinical study indicate this approach is a powerful and exciting technique for identification of pathogens. The menu of models is being expanded to include other bacterial genera and species of clinical significance.
Accurate characterization of the optical properties of erythrocytes is essential for the applications in optical biomedicine,
in particular, for diagnosis of blood related diseases. The observed optical properties strongly depend on the
erythrocyte's size, hemoglobin composition and orientation relative to the incident light. We explored the effect of
orientation on the absorption and scattering properties of erythrocytes suspended in saline using UV-visible spectroscopy
and theoretical predictive modeling based on anomalous diffraction approximation. We demonstrate that the orientation
of erythrocytes in dilute saline suspensions is not random and produces consistent spectral pattern. Numerical analysis
showed that the multi-wavelength absorption and scattering properties of erythrocytes in dilute suspensions can be
accurately described with two orientation populations. These orientation populations with respect to the incident light are
face-on incidence and edge-on incidence. The variances of the orientation angles for each population are less than 15
degrees and the relative proportions of the two populations strongly depend on the number density of the erythrocytes in
suspensions. Further, the identified orientation populations exhibit different sensitivities to the changes in the
compositional and morphological properties of erythrocytes. The anomalous diffraction model based on these orientation
populations predicts the absorption and scattering properties of erythrocytes with accuracy greater than 99%.
Establishment of the optical properties of normal erythrocytes allows for detection of the disease induced changes in the
erythrocyte spectral signatures.
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