Magneto Hydrodynamic and Microwave Measurements for Label Free Detection and Differentiation of Bacterial Pathogens

Abstract

A comprehensive understanding of the dynamics of social interactions in bacterial species is important for the effective management and control of infectious diseases. Owing to the time lag in identifying the etiology of infectious diseases, the practice of often indiscriminate use of broad-spectrum antibiotics has led to the genesis of drug-resistant strains. Therefore, it is necessary to develop methods for instant detection and identification of pathogens. In addition to the diagnosis of the causal agents, validating the quality of the pharmaceuticals being used is also necessary to avoid treatment failures. In this thesis, surface charge properties and electrophoretic mobility of Escherichia coli, Staphylococcus aureus and Salmonella Typhimurium were probed through zeta potential measurements. We have also studied the variation in the zeta potential of bacterial cells due to prolonged incubation and a systematic mixing with other species. Our experimental findings suggest that when grown in the same type of broth media under the same physical environment, different bacterial species exhibit different zeta potentials that can be used as a biomarker for the identification of isolated strains. However, in the case of mixed cultures, the deviation of the zeta potential from the expected superposed averages accounts for the interaction between the species mixed. The results were verified with the standard agar plating method. To study the growth dynamics of consortia of bacterial species co-cultured on the same chromogenic agar media, a computer vision tool has been developed, which can aid in understanding the social interactions in a bacterial cohort. Owing to the re-distribution of the surface charges due to social interactions, the efficacy of antibiotic agents may get severely affected. This hypothesis has also been verified using eleven different antibiotics through the standard Bauer-Kirby s method. Furthermore, three different cost-effective sensing platforms based on a microstrip ring resonator for screening of liquid samples, a visible range spectrophotometer for real-time monitoring of bacterial growth and a microwave cavity perturbation-based sensor for the detection of counterfeit drugs have been described in this doctoral work. The applications, limitations and the future aspects of each method have been discussed thoroughly in the main body of the thesis. newline