Peter G. Stroot

Swelling-induced instabilities in microscale, surface-confined poly(N-isopropylacryamide) hydrogels

A hydrogel is a three-dimensional hyperelastic polymer network that swells to a specific volume upon exposure to a penetrating solvent. If mechanical constraints interfere with the swelling process, anisotropic compressive stresses are generated, which may manifest in local or global instabilities. Herein, we employ confocal microscopy for the in situ, three-dimensional study of micron-scale hydrogels that are pinned to a solid substrate. Depending on the initial geometry of the hydrogel, four general modes of swelling-induced deformation were found: lateral differential swelling, local sinusoidal edge buckling, bulk sinusoidal buckling, and surface creasing. The transition between local edge buckling and bulk buckling is consistent with linear elastic theory; however, linear theory cannot be used to predict many details of the swollen structures. Whereas global buckling has a well-defined wavelength that depends on height of the hydrogel structure, edge buckling appears to be independent of height and depends on sample history. Moreover, edge buckling can appear in globally buckled structures, suggesting two different mechanisms for the two instabilities.

Removal of sediment and bacteria from water using green chemistry.

Although nearly all newly derived water purification methods have improved the water quality in developing countries, few have been accepted and maintained for long-term use. Field studies indicate that the most beneficial methods use indigenous resources, as they are both accessible and accepted by communities they help. In an effort to implement a material that will meet community needs, two fractions of mucilage gum were extracted from the Opuntia ficus-indica cactus and tested as flocculation agents against sediment and bacterial contamination. As diatomic ions are known to affect both mucilage and promote cell aggregation, CaCl(2) was studied in conjunction and compared with mucilage as a bacteria removal method. To evaluate performance, ion-rich waters that mimic natural water bodies were prepared. Column tests containing suspensions of the sediment kaolin exhibited particle flocculation and settling rates up to 13.2 cm/min with mucilage versus control settling rates of 0.5 cm/min. Bacillus cereus tests displayed flocculation and improved settling times with mucilage concentrations lower than 5 ppm and removal rates between 97 and 98% were observed for high bacteria concentration tests (>10(8) cells/ml). This natural material not only displays water purification abilities, but it is also affordable, renewable and readily available.

Determination of Specific Growth Rate by Measurement of Specific Rate of Ribosome Synthesis in Growing and Nongrowing Cultures of Acinetobacter calcoaceticus

ABSTRACT RT-RiboSyn measures the specific rate of ribosome synthesis in distinct microbial populations by measuring the generation rate of precursor 16S rRNA relative to that of mature 16S rRNA when precursor 16S rRNA processing is inhibited. Good agreement was demonstrated between specific rate of ribosome synthesis and specific growth rate of Acinetobacter calcoaceticus.

Capture antibody targeted fluorescence in situ hybridization (CAT-FISH): Dual labeling allows for increased specificity in complex samples

Pathogen detection using biosensors is commonly limited due to the need for sensitivity and specificity in detecting targets within mixed populations. These issues were addressed through development of a dual labeling method that allows for both liquid-phase fluorescence in situ hybridization (FISH) and capture antibody targeted detection (CAT-FISH). CAT-FISH was developed using Escherichia coli O157:H7 and Staphylococcus aureus as representative bacteria, and processing techniques were evaluated with regard to FISH intensities and antibody recognition. The alternative fixative solution, methacarn, proved to be superior to standard solid-phase paraformaldehyde fixation procedures, allowing both FISH labeling and antibody recognition. CAT-FISH treated cells were successfully labeled with FISH probes, captured by immunomagnetic separation using fluorescent cytometric array beads, and detected using a cytometric array biosensor. CAT-FISH treated cells were detectable with LODs comparable to the standard antibody-based technique, (~10(3)cells/ml in PBS), and the technique was also successfully applied to two complex matrices. Although immunomagnetic capture and detection using cytometric arrays were demonstrated, CAT-FISH is readily applicable to any antibody-based fluorescence detection platform, and further optimization for sensitivity is possible via inclusion of fluorescently tagged antibodies. Since the confidence level needed for positive identification of a detected target is often paramount, CAT-FISH was developed to allow two separate levels of specificity, namely nucleic acid and protein signatures. With proper selection of FISH probes and capture antibodies, CAT-FISH may be used to provide rapid detection of target pathogens from within complex matrices with high levels of confidence.

Association of the Genus Acinetobacter with the Decomposition of a Swine Carcass and the Isolation and Characterization of a Novel Strain of Acinetobacter sp. P4

Using fluorescence in situ hybridization (FISH) and a selective and differential medium, Acinetobacter numbers were enumerated over the time course of decomposition, from fresh to putrid/dry, of a swine carcass. In addition, Acinetobacter diversity and succession were also characterized. Acinetobacter bacterial counts were observed to be the lowest before exposure (undetectable) and increased to their highest during active decay then decreased and leveled during advanced decay through putrid/dry. FISH analysis revealed Acinetobacter cells were mostly clustered together, which is consistent with growth in a non-mixed environment, such as soil. The abundance of Acinetobacter cells decreased from active decomposition to putrid/dry. BLAST analysis using the 16S rRNA-gene sequence identified the isolates as one of the following Acinetobacter spp: A. baumannii, A. haemolyticus, A. junii, A. johnsonii, and A. gerneri. Phenotypic description of the identified isolates closely matched those of known genomic species. One isolate, P4, was observed to be unique in its phenotypic and phylogenetic characteristics and was more closely related to A. sp E10. The isolates from this study displayed multi-antibiotic resistance. The results from the study revealed the association of Acinetobacter spp. with that of carrion which adds to our knowledge of the ecology of this genus along with the potential implications of infection for this opportunistic pathogen.