Detection of extended-spectrum β-lactamase (ESBL) and plasmid-borne blaCTX-M and blaTEM genes among clinical strains of Escherichia coli isolated from patients in the north of Iran

Escherichia coli is an important cause of hospital-acquired infections worldwide. Antimicrobial resistance leads to treatment failure of hospital infections caused by E. coli. Production of extended-spectrum β-lactamases (ESBLs) is one of the major causes of antibiotic resistance in these bacteria. This study aimed to investigate the frequency of blaTEM and blaCTX-M genes in ESBL-producing E. coli strains isolated from clinical specimens of patients admitted to six hospitals in the north of Iran. A total of 160 E. coli strains were isolated from various clinical samples of hospitalised patients. Antibiotic resistance patterns were determined by the Kirby�Bauer disk diffusion method. The double-disk phenotypic confirmatory test was carried out amongst β-lactam-resistant isolates to detect ESBL-producing strains. Plasmid DNA of ESBL-producing strains was extracted and subjected to PCR for detection of the blaTEM and blaCTX-M genes, and isolates were extensively verified by sequencing. The highest resistance rate was to amoxicillin; all E. coli isolates (100) were susceptible to imipenem. Amongst the 160 clinical E. coli isolates, 83 (51.9) were ESBL-positive, of which 27 (32.5) and 72 (86.7) were positive for blaTEM and blaCTX-M, respectively. This study is the first report of an ESBL phenotype disseminated in hospitals in the north of Iran. These findings showed that there was a direct relationship between the development of resistance to β-lactam antibiotics and production of TEM and CTX-M enzymes. © 2016 International Society for Chemotherapy of Infection and Cance

Photochemically induced crosslinking of tarsal collagen as a treatment for eyelid laxity: assessing potentiality in animal tissue

PURPOSE: An experimental study to demonstrate in animal eyelids that the controlled exposure of excised tarsal plate to ultraviolet-A radiation can induce a rigidification effect due to photochemical crosslinking of the constitutive collagen.METHODS: Excised strips of sheep tarsus were irradiated with ultraviolet-A rays (wavelength 365 nm) at low and high irradiances, in the presence of riboflavin as a photosensitizer, using radiation sources available for corneal collagen crosslinking procedure. The tensile strength and Young's modulus (stiffness) of irradiated and control samples were measured in a mechanical tester and analyzed statistically. Histologic examination of the specimens was carried out to evaluate the effect of radiation on the meibomian glands and collagen organization.RESULTS: Mechanical evaluation showed that irradiation induced both stiffening and strengthening of the tarsal plate specimens, and this effect was enhanced at the higher levels of irradiance. The changes in mechanical properties can be attributed to a process of photochemically induced crosslinking of tarsal collagen. Histology revealed no changes in the meibomian glands or in the fibrous collagen system of the tarsus.CONCLUSIONS: These findings indicate that irradiation of tarsal collagen leading to tissue stiffening could be a safe procedure for treating lax eyelid conditions in human patients

Diameter-dependent elastic properties of carbon nanotube-polymer composites: Emergence of size effects from atomistic-scale simulations

We propose a computational procedure to assess size effects in nonfunctionalized single-walled carbon nanotube (CNT)-polymer composites. The procedure upscales results obtained with atomistic simulations on a composite unit cell with one CNT to an equivalent continuum composite model with a large number of CNTs. Molecular dynamics simulations demonstrate the formation of an ordered layer of polymer matrix surrounding the nanotube. This layer, known as the interphase, plays a central role in the overall mechanical response of the composite. Due to poor load transfer from the matrix to the CNT, the reinforcement effect attributed to the CNT is negligible; hence the interphase is regarded as the only reinforcement phase in the composite. Consequently, the mechanical properties of the interface and the CNT are not derived since their contribution to the elastic response of the composite is negligible. To derive the elastic properties of the interphase, we employ an intermediate continuum micromechanical model consisting of only the polymer matrix and a three-dimensional fiber representing the interphase. The Young's modulus and Poisson's ratio of the equivalent fiber, and therefore of the interphase, are identified through an optimization procedure based on the comparison between results from atomistic simulations and those obtained from an isogeometric analysis of the intermediate micromechanical model. Finally, the embedded reinforcement method is employed to determine the macroscopic elastic properties of a representative volume element of a composite with various fiber volume fractions and distributions. We then investigate the role of the CNT diameter on the elastic response of a CNT-polymer composite; our simulations predict a size effect on the composite elastic properties, clearly related to the interphase volume fraction.Applied Mechanic