Adsorption of fluorescent labeled E. coli in selected vegetative buffer systems
Authors:   , Al-Awwal Nasruddeen 
Published: February 2023

Environmental pathogen contamination in water resources is one of the major water quality concerns throughout the world. There is growing increase in concern and interest for controlling water-borne pathogens in water resources. However, in most cases, the first landing zone for pathogens is soil, from which they transport into the water. Increasing global industrialization and polluting soil with contaminants from both agricultural processes and industrial waste products has caused several life-threatening diseases. Hence, understanding the processes on how to overcome the contaminations in soils and using rapid and reliable pathogen detection methods will help in mitigating the contamination posing threats to humanity. The major food-and-water-borne pathogens like Salmonella enterica, Escherichia coli, Vibrio cholerae, Campylobacter jejuni, Shigella spp., enterotoxigenic, Clostridium difficile, Listeria monocytogenes are presenting threats to over 600 million people worldwide, almost 1 in 10 persons. The Conventional methods for pathogen detection tend to rely on specific microbiological and biochemical identification which involves a length process, prone to contamination, and sometimes can lack sensitivity and specificity, and it also requires specialized equipment and well-trained personnel and is therefore costly. Normally, samples such as food, urine, blood are sent for microbiological analysis using various techniques, namely, cell culture methods, microscopy and, biochemical assays, immunological tests, or genetic analysis. However, the molecular approaches that involve near-time or real-time bacterial detection are rapid, sensitive, and specific for the target pathogen. The objectives of this study were: 1) To design a nanobiosensor that is capable of specifically detecting E. coli O157:H7 in contaminated water samples; 2) to investigate the potential of utilizing two fluorophores namely, Fluorescein isothiocyanate (FITC) and Tetramethyl rhodamine isothiocyanate (TRITC) in detecting E. coli O157:H7 in food samples using Foster Resonance Energy Transfer (FRET) technique; and 3) to evaluate E. coli O157:H7 - GFP adsorption processes in agroforestry buffer (AB), grass buffer (GB), and row crop (RC) soil management to better understand which management treatment can help in mitigating the effects on E. coli transport to water resources from contaminated lands. The results of the first study showed that the nanobiosensor with its ease of assembly can act as potential tool to assist in monitoring the presence of pathogens especially in the water and food industries as it is fast for detection of E. coli O157:H7. Even though there is a need for optimizing the sensor by increasing its sensitivity and decreasing false positive results, it still demonstrated rapid assessment in which tests were conducted at near real-time with results obtained using the biosensor assay within 5 min. This method reduced both the enrichment (6-h) and the detection times when compared to the available detection methods in the FDA, 2015 guidelines. The second study outcomes revealed that the FRET technique can be applicable in detecting the range of E. coli O157:H7 concentrations at selected pH values, with the help of fluorescent microscopy, the results demonstrated an optimal pH which the E. coli O157:H7 can survive, hence an excellent range of pH for its detection. The results also revealed that the fluorescent signal is indirectly proportion with the pH, with optimal pH having the highest intensity and more pronounced fluorescent spectroscopic images. The signal decreases as the pH increases. The pair of fluorophores demonstrated good Stokes shift, sharply spike emission wavelength, and easily conjugated which are some of the most important properties needed for FRET pairs. The results from the third study indicated that the Freundlich isotherm model have preeminence to both Langmuir and Temkin isotherms for explaining the adsorption of E. coli on the three soil treatments. Based on the Freundlich 1/nf values, results indicated that the adsorption occurred on heterogeneous surfaces of the adsorbent. The coefficients of determination values, R2 of the Temkin model obtained in this work were less than those of both Freundlich and Langmuir models. BT parameter values indicated that BT [greater than] 8 kJ/mol, indicated a chemical adsorption (chemisorption). This study concluded that the agroforestry buffer management practices not only can be used to mitigate the effect of excess nutrients from polluting water bodies but also bacteria such as E. coli O157:H7 - GFP from contaminating the water sources. The study also provides an insight in understanding of adsorption of E. coli O157:H7-GFP under different management practices and demonstrated that the agroforestry buffer system practices can help in enhancing both soil and water quality.