Aims: To examine cellular injuries occurring in cells of Escherichia coli (Gram-negative bacteria) and Lactobacillus rhamnosus (Gram-positive bacteria) in response to a high-intensity ultrasound treatment using classical plate count technique and flow cytometry. Method and Results: According to plate count results, E. coli (D-value 8AE3 min) was far more sensitive than L. rhamnosus (D-value 18AE1 min) in their response to the ultrasound intensity applied (20 kHz, 17AE6 W). The dye precursor carboxyfluorescein diacetate (cFDA) could freely diffuse across the cytoplasmic membrane of intact cells of Gram-positive bacteria L. rhamnosus, resulting in its intracellular enzymatic conversion and emission of green fluorescence. In contrast, the presence of an outer membrane on E. coli, which represents the class of Gram-negative bacteria, apparently disabled the penetration of viability marker cFDA. Ultrasound application on E. coli yielded in an increasing population with disintegrated outer membrane, which allowed penetration of cFDA and its intracellular enzymatic conversion as well as accumulation. In both organisms evaluated only a small population was labelled by propidium iodide upon exposure to ultrasound for up to 20 min. Within the experimental conditions investigated ultrasound did not considerably affect the cytoplasmic membrane, although according to plate count results viability loss occurred. Conclusions:The results compiled suggest, that ultrasound induced cell death, which may not be related to membrane damage. Significance and Impact of the Study: Limitation on the use of bacteriocins, which are aimed on destabilization of cytoplasmic membrane but inhibited by the outer membrane, could be overcome by ultrasound-assisted physical disruption of the outer membrane.

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The hydroisomerization of hexane on platinum-loaded acidic zeolites was studied with positron emission profiling (PEP), a tracer imaging technique based on the same principle as positron emission tomography. The unique character of PEP enables the determination of reaction parameters under in situ reaction conditions that are difficult to obtain via ex situ techniques. A numerical model, including the effects of adsorption, diffusion, and reaction, was used to fit the measured concentration profiles. Preexponential factors and activation energies for some of the elementary proton-activated reaction steps of the bifunctional reaction mechanism have been determined in different transient experiments for a variety of platinum-loaded acidic zeolites. An activation energy for dehydrogenation of 98 kJ/mol was found, in which the heat of adsorption appeared to be included. The heat of adsorption was found to be 61 kJ/mol. An upper value for the deprotonation energy of 100 kJ/mol was determined. This is in agreement with quantum mechanical calculations that have become available only recently.

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