We analyzed the distribution of phylogenetic groups of foodborne Escherichia coli isolates. We also investigated the prevalence of virulence-associated genes of diarrheagenic E. coli. In total, 162 E. coli isolated from foods (raw meat, fish, and processed foods) were collected in Korea. Approximately 90% of the foodborne isolates belonged to phylogenetic groups A and B1, whereas 1.2% were allocated to group B2, and 9.3% to D. Multiplex polymerase chain reaction (PCR) assays were used to detect the following: stx (1) and stx (2) to identify Shiga toxin-producing E. coli (STEC), eae and bfpA to identify enteropathogenic E. coli (EPEC), ipaH for enteroinvasive E. coli, CVD432 for enteroaggregative E. coli, and lt and st for enterotoxigenic E. coli (ETEC). The presence of daaD in diffusely adherent E. coli was examined by singleplex PCR. Of the 162 foodborne E. coli isolates, three (1.9%) were confirmed to be pathogenic E. coli: STEC, ETEC, and atypical EPEC based on their possession of stx (1), st, and eae, and the pathogenic strains were isolated in beef, rockfish, and pork, respectively. Molecular typing was conducted by multilocus sequence typing to investigate the genetic relationships among the pathogenic strains. All isolates positive for virulence genes had different mulilocus sequence typing profiles representing different sequence types (ST) of ST101, ST1815, and ST1820. These results indicate that some food samples were contaminated with pathogenic E. coli.
To analyze the effect of the pore size of graphite in a pore-forming agent, graphite was added to porous ceramics of Al 2 O 3-SiO 2-ZrO 2 systems. The graphite had 45~75, 100~125, 150~180, and 75~180㎛ dimensions. The properties of the ceramics, such as apparent porosity, density, dynamic elastic modulus, mechanical strength, and permeability, were investigated. The average pore size increased from 15.35㎛ to 22.32㎛ with the increase of the graphite size. The sample with the largest average pore size showed the highest mechanical strength and gas permeability. This was due to the sample with the largest pore size at the same porosity having fewer pores and larger distance between the pores than the sample with the smallest pore size, making cracks less likely to propagate. In addition, the large pore size reduced the repulsive power originating from the drag force between the gas and internal pore walls.
The mechanical properties and molecular structure of rubber materials for reducing the vibration of elevator cabins were studied with respect to the hardnesses change to confirm the degradation behavior by temperature (85 ℃) and humidity (85% R.H.). To examine the effects of hardness on the mechanical properties after thermal and hydrothermal aging, the international rubber hardness degree (IRHD), tensile strength, and elongation % were compared with the elastic modulus as a function of degradation time. The microstructure showed that the crack growth of the rubber material with high hardness was fast after hydrothermal aging. It originated from a C = C bonding decrease, and the C = O and CO -C bonding were increased by the penetration of humidity. In the results of solid-state 13 C nuclear magnetic resonance (NMR) spectroscopy to confirm the molecular structure, several peaks were assigned to respective vulcanized structures along with mechanical properties. Therefore, the degradation behavior after thermal/ hydrothermal aging was different according to low/high hardness: The mechanical properties of the rubber material with high hardness rapidly decreased due to the high density of cross-links and chain scission.
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