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Shigellosis is one of the major public health concerns in developing and low-income countries caused by four species of Shigella. There is an apparent need to develop rapid, cost-effective, sensitive and specific methods for differentiation of Shigella species to be used in outbreaks and health surveillance systems. We developed a sensitive and specific Fourier-transform infrared spectroscopy (FTIR) based method followed by principal component analysis (PCA) and hierarchical clustering analysis (HCA) assays to differentiate four species of Shigella isolates from stool samples. The FTIR based method was evaluated by differentiation of 91 Shigella species from each other in clinical samples using both gold standards (culture-based and agglutination methods) and developed FTIR assay; eventually, the sensitivity and specificity of the developed method were calculated. In summary, four distinct FTIR spectra associated with four species of Shigella were obtained with wide variations in three definite regions, including 1800–1550 cm−1, 1550–1100 cm−1, and 1100–800 cm−1 distinguish these species from each other. In this study, we found the FTIR method followed by PCA analysis with specificity, sensitivity, differentiation error and correct differentiation rate values of 100, 100, 0 and 100%, respectively, for identification and differentiation of all species of the Shigella in stool samples.

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The binding parameters between cyclodextrins (CDs) and human serum albumin (HSA) were investigated by isothermal titration calorimetry (ITC), fluorescence quenching, and UV-vis absorption spectroscopy at 300 K in 50 mM phosphate buffer solution. Among the various CDs investigated, b-CD has the greater ability to decrease the aggregation of HSA and the results indicated that the inhibition order is g-CD , a-CD , b-CD. The obtained heats for HSAþCDs interactions were reported and analysed in terms of the extended solvation model, which was used to reproduce the enthalpies of HSA interactions with CDs over a broad range of complex concentrations. The binding constant and thermodynamic parameters were obtained. These suggested that the binding reaction was driven by both enthalpy and entropy, and electrostatic interactions played a major role in the stabilising of HSA. The parameters d y A and d y B reflected the net effect of b-CD on the HSA stability at low and high cyclodextrin concentrations, respectively. The positive values for d y A indicated that b-CD stabilises the HSA structure at low concentrations. The UV absorption intensity of theses complexes increased and a slight red shift was observed in the absorbance wavelength with increasing the CD concentration. The fluorescence intensity of HSA decreased regularly and a slight blue shift was observed for the emission wavelength with increasing CD concentration. The results indicate that the CD complex could quench the fluorescence of HSA and changes the microenvironment of the tryptophan residue.