Two Atypical Enteropathogenic Escherichia coli Strains Induce the Production of Secreted and Membrane-Bound Mucins To Benefit Their Own Growth at the Apical Surface of Human Mucin-Secreting Intestinal HT29-MTX Cells

In rabbit ligated ileal loops, two atypical enteropathogenic Escherichia coli (aEPEC) strains, 3991-1 and 0421-1, intimately associated with the cell membrane, forming the characteristic EPEC attachment and effacement lesion of the brush border, induced a mucous hypersecretion, whereas typical EPEC (tEPEC) strain E2348/69 did not. Using cultured human mucin-secreting intestinal HT29-MTX cells, we demonstrate that apically aEPEC infection is followed by increased production of secreted MUC2 and MUC5AC mucins and membrane-bound MUC3 and MUC4 mucins. The transcription of the MUC5AC and MUC4 genes was transiently upregulated after aEPEC infection. We provide evidence that the apically adhering aEPEC cells exploit the mucins` increased production since they grew in the presence of membrane-bound mucins, whereas tEPEC did not. The data described herein report a putative new virulence phenomenon in aEPEC.

Characterization by restriction fragment length polymorphism and sequence analysis of field and vaccine strains of infectious laryngotracheitis virus involved in severe outbreaks

At the end of 2002 and throughout 2003, there was a severe outbreak of infectious laryngotracheitis (ILT) in an intensive production area of commercial hens in the Sao Paulo State of Brazil. ILT virus was isolated from 28 flocks, and 21 isolates were genotyped by polymerase chain reaction and restriction fragment length polymorphism (PCR-RFLP) using four genes and eight restriction enzymes, and by partial sequencing of the infected cell protein 4 (ICP4) and thymidine kinase (TK) genes. Three groups resulted from the combinations of PCR-RFLP patterns: 19 field isolates formed Group I, and the remaining two isolates together with the chicken embryo origin (CEO) vaccine strains formed Group II. Group III comprised the tissue-culture origin (TCO) vaccine strain by itself. The PCR-RFLP results agreed with the sequencing results of two ICP4 gene fragments. The ICP4 gene sequence analysis showed that the 19 field isolates classified into Group I by RFLP-PCR were identical among themselves, but were different to the TCO and CEO vaccines. The two Group II isolates could not be distinguished from one of the CEO vaccines. The nucleotide and amino acid sequence analyses discriminated between the Brazilian and non-Brazilian isolates, as well as between the TCO and CEO vaccines. Sequence analysis of the TK gene enabled classification of the field isolates (Group I) as virulent and non-vaccine. This work shows that the severe ILT outbreak was caused by a highly virulent, non-vaccine strain.

Differentiation of field isolates and vaccine strains of infectious laryngotracheitis virus by DNA sequencing

Two different regions of the infected cell protein 4 (ICP4) gene of infectious laryngotracheitis virus (ILTV) were amplified and sequenced for characterization of field isolates and tissue culture-origin (TCO) and chicken embryo-origin (CEO) vaccine strains. Phylogenetic analysis of the two regions showed differences in nucleotide and amino acid sequences between field isolates and attenuated vaccines. The PCR-RFLP results were identical to those obtained by DNA sequencing and validated their use to differentiate ILTV strains. The approach using the sequencing of the two fragments of the ICP4 gene showed to be an efficient and practical procedure to differentiate between field isolates and vaccine strains of ILTV. (C) 2009 Elsevier Ltd. All rights reserved.

Escherichia coli strains of serotype O51 : H40 comprise typical and atypical enteropathogenic E. coli strains and are potentially diarrheagenic

Escherichia coli strains of serotype O51:H40 were studied with regard to the presence of several virulence properties and their genetic diversity and enteropathogenicity in rabbit ileal loops. This serotype encompasses potential enteropathogenic strains mostly classified as being atypical enteropathogenic E. coli (EPEC) strains, which are genetically closer to enterohemorrhagic E. coli than to typical EPEC strains.

A critical view on biaxial and short-beam uniaxial flexural strength tests applied to resin composites using Weibull, fractographic and finite element analyses

Objective. To evaluate the biaxial and short-beam uniaxial strength tests applied to resin composites based upon their Weibull parameters, fractographic features and stress distribution. Methods. Disk- (15 mm x 1 mm) and beam-shaped specimens (10 mm x 2 mm x 1 mm) of three commercial composites (Concept/Vigodent, CA; Heliomolar/Ivoclar-Vivadent, HE; Z250/3M ESPE, FZ) were prepared. After 48h dry storage at 37 degrees C, disks and beams were submitted to piston-on-three-balls (BI) and three-point bending (UNI) tests, respectively. Data were analyzed by Weibull statistics. Fractured surfaces were observed under stereomicroscope and scanning electron microscope. Maximum principal stress (sigma(1)) distribution was determined by finite element analysis (FEA). Maximum sigma(1-BI) and sigma(1-UNI) were compared to FZ strengths calculated by applying the average failure loads to the analytical equations (sigma(a-BI) and sigma(a-UNI)). Results. For BI, characteristic strengths were: 169.9a (FZ), 122.4b (CA) and 104.8c (HE), and for UNI were: 160.3a (FZ), 98.2b (CA) and 91.6b (HE). Weibull moduli ( m) were similar within the same test. CA and HE presented statistically higher m for BI. Surface pores ( BI) and edge flaws ( UNI) were the most frequent fracture origins. sigma(1-BI) was 14% lower than sigma(a-BI.) sigma(1-UNI) was 43% higher than sigma(a-UNI). Significance. Compared to the short-beam uniaxial test, the biaxial test detected more differences among composites and displayed less data scattering for two of the tested materials. Also, biaxial strength was closer to the material`s strength estimated by FEA. (C) 2009 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.

Vertical Root Fracture in Upper Premolars with Endodontic Posts: Finite Element Analysis

Upper premolars restored with endodontic posts present a high incidence of vertical root fracture (VRF). Two hypotheses were tested: (1) the smaller mesiodistal diameter favors stress concentration in the root and (2) the lack of an effective bonding between root and post increases the risk of VRF. Using finite element analysis, maximum principal stress was analyzed in 3-dimensional intact upper second premolar models. From the intact models, new models were built including endodontic posts of different elastic modulus (E = 37 or E = 200 GPa) with circular or oval cross-section, either bonded or nonbonded to circular or oval cross-section root canals. The first hypothesis was partially confirmed because the conditions involving nonbonded, low-modulus posts showed lower tensile stress for oval canals compared to circular canals. Tensile stress peaks for the nonbonded models were approximately three times higher than for the bonded or intact models, therefore confirming the second hypothesis. (J Endod 2009;35:117-120)

Finite Element Analysis of Shear Versus Torsion Adhesive Strength Tests for Dental Resin Composites

Stress distributions in torsion and wire-loop shear tests were compared using three-dimensional (3-D) linear-elastic finite element method, in an attempt to predict the ideal conditions for testing adhesive strength of dental resin composites to dentin. The torsion test presented lower variability in stress concentration at the adhesive interface with changes in the proportion adhesive thickness/resin composite diameter, as well as lower variability with changes in the resin composite elastic modulus. Moreover, the torsion test eliminated variability from changes in loading distance, and reduced the cohesive fracture tendency in the dentin. The torsion test seems to be more appropriate than wire-loop shear test for testing the resin composite-tooth interface strength. (c) Koninklijke Brill NV, Leiden, 2009

Finite-Element Analysis of Stress on Dental Implant Prosthesis

Background: Understanding how clinical variables affect stress distribution facilitates optimal prosthesis design and fabrication and may lead to a decrease in mechanical failures as well as improve implant longevity. Purpose: In this study, the many clinical variations present in implant-supported prosthesis were analyzed by 3-D finite element method. Materials and Method: A geometrical model representing the anterior segment of a human mandible treated with 5 implants supporting a framework was created to perform the tests. The variables introduced in the computer model were cantilever length, elastic modulus of cancellous bone, abutment length, implant length, and framework alloy (AgPd or CoCr). The computer was programmed with physical properties of the materials as derived from the literature, and a 100N vertical load was used to simulate the occlusal force. Images with the fringes of stress were obtained and the maximum stress at each site was plotted in graphs for comparison. Results: Stresses clustered at the elements closest to the loading point. Stress increase was found to be proportional to the increase in cantilever length and inversely proportional to the increase in the elastic modulus of cancellous bone. Increasing the abutment length resulted in a decrease of stress on implants and framework. Stress decrease could not be demonstrated with implants longer than 13 mm. A stiffer framework may allow better stress distribution. Conclusion: The relative physical properties of the many materials involved in an implant-supported prosthesis system affect the way stresses are distributed.

Finite Element Analysis of 2 Immediate Loading Systems in Edentulous Mandible: Rigid and Semirigid Splinting of Implants

Purpose: The objective of this study was to evaluate the stress on the cortical bone around single body dental implants supporting mandibular complete fixed denture with rigid (Neopronto System-Neodent) or semirigid splinting system (Barra Distal System-Neodent). Methods and Materials: Stress levels on several system components were analyzed through finite element analysis. Focusing on stress concentration at cortical bone around single body dental implants supporting mandibular complete fixed dentures with rigid ( Neopronto System-Neodent) or semirigid splinting system ( Barra Distal System-Neodent), after axial and oblique occlusal loading simulation, applied in the last cantilever element. Results: The results showed that semirigid implant splinting generated lower von Mises stress in the cortical bone under axial loading. Rigid implant splinting generated higher von Mises stress in the cortical bone under oblique loading. Conclusion: It was concluded that the use of a semirigid system for rehabilitation of edentulous mandibles by means of immediate implant-supported fixed complete denture is recommended, because it reduces stress concentration in the cortical bone. As a consequence, bone level is better preserved, and implant survival is improved. Nevertheless, for both situations the cortical bone integrity was protected, because the maximum stress level findings were lower than those pointed in the literature as being harmful. The maximum stress limit for cortical bone (167 MPa) represents the threshold between plastic and elastic state for a given material. Because any force is applied to an object, and there is no deformation, we can conclude that the elastic threshold was not surpassed, keeping its structural integrity. If the force is higher than the plastic threshold, the object will suffer permanent deformation. In cortical bone, this represents the beginning of bone resorption and/or remodeling processes, which, according to our simulated loading, would not occur. ( Implant Dent 2010; 19:39-49)

Beef Carcass Contamination by Shiga Toxin-Producing Escherichia coli Strains in an Abattoir in Brazil: Characterization and Resistance to Antimicrobial Drugs

A survey was performed to estimate the frequency of Escherichia coli and Shiga toxin-producing E. coli (STEC) in carcasses obtained from an abattoir in Brazil between February 2006 and June 2007. A total of 216 beef carcasses were sampled at three stages of the slaughter process-preevisceration, postevisceration, and postprocessing-during the rain and dry seasons, respectively. Of the carcasses sampled, 58%, were preevisceration E. coli positive, 38% were postevisceration positive, and 32% postprocessing positive. At the postprocessing stage, the isolation of E. coli was twice as high in the rain season. E. coli was isolated from 85 carcasses of which only 3 (1.4%) were positive for stx-encoding genes. No E. coli O157 serogroup isolates were detected. No antimicrobial resistance was found in nine of the isolates (10% of the total). The most frequent resistances were seen against cephalothin (78%), streptomycin (38%), nalidixic acid (36%), and tetracycline (30%). Multidrug resistance (MDR) to three or more antimicrobial agents was determined in 28 (33%) E. coli isolates. The presence of STEC and MDR strains among the isolates in the beef carcasses emphasizes the importance of proper handling to prevent carcass contamination.

Diffusion modeling of percutaneous absorption kinetics: 2. Finite vehicle volume and solvent deposited solids

The diffusion model for percutaneous absorption is developed for the specific case of delivery to the skin being limited by the application of a finite amount of solute. Two cases are considered; in the first, there is an application of a finite donor (vehicle) volume, and in the second, there are solvent-deposited solids and a thin vehicle with a high partition coefficient. In both cases, the potential effect of an interfacial resistance at the stratum corneum surface is also considered. As in the previous paper, which was concerned with the application of a constant donor concentration, clearance limitations due to the viable eqidermis, the in vitro sampling rate, or perfusion rate in vivo are included. Numerical inversion of the Laplace domain solutions was used for simulations of solute flux and cumulative amount absorbed and to model specific examples of percutaneous absorption of solvent-deposited solids. It was concluded that numerical inversions of the Laplace domain solutions for a diffusion model of the percutaneous absorption, using standard scientific software (such as SCIENTIST, MicroMath Scientific software) on modern personal computers, is a practical alternative to computation of infinite series solutions. Limits of the Laplace domain solutions were used to define the moments of the flux-time profiles for finite donor volumes and the slope of the terminal log flux-time profile. The mean transit time could be related to the diffusion time through stratum corneum, viable epidermal, and donor diffusion layer resistances and clearance from the receptor phase. Approximate expressions for the time to reach maximum flux (peak time) and maximum flux were also derived. The model was then validated using reported amount-time and flux-time profiles for finite doses applied to the skin. It was concluded that for very small donor phase volume or for very large stratum corneum-vehicle partitioning coefficients (e.g., for solvent deposited solids), the flux and amount of solute absorbed are affected by receptor conditions to a lesser extent than is obvious for a constant donor constant donor concentrations. (C) 2001 Wiley-Liss, Inc. and the American Pharmaceutical Association J Pharm Sci 90:504-520, 2001.

Dengue virus binding to human leukocyte cell lines: receptor usage differs between cell types and virus strains

Monocyte macrophages (M phi) are thought to be the principal target cells for the dengue viruses (DV), the cause of dengue fever and hemorrhagic fever. Cell attachment is mediated by the virus envelope (E) protein, but the host-cell receptors remain elusive. Currently, candidate receptor molecules include proteins, Fc receptors, glycosaminoglycans (GAGs) and lipopolysaccharide binding CD14-associated molecules. Here, we show that in addition to M phi, cells of the T- and B-cell lineages, and including cells lacking GAGs, can bind and become infected with DV. The level of virus binding varied widely between cell lines and, notably, between virus strains within a DV serotype. The latter difference may be ascribable to one or more amino acid differences in domain II of the E protein. Heparin had no significant effect on DV binding, while heparinase treatment of cells in all cases increased DV binding, further supporting the contention that GAGs are not required for DV binding and infection of human cells. In contrast to a recent report, we found that lipopolysaccharide (LPS) had either no effect or enhanced DV binding to, and infection of various human leukocyte cell lines, while in all virus-cell combinations, depletion of Ca2+/Mg2+ enhanced DV binding. This argues against involvement of beta (2) integrins in virus-host cell interactions, a conclusion in accord with the demonstration of three virus binding membrane proteins of < 75 kDa. Collectively, the results of this study question the purported exclusive importance of the E protein domain III in DV binding to host cells and point to a far more complex interaction between various target cells and, notably, individual DV strains. (C) 2001 Elsevier Science B.V. All rights reserved.