Background: Pseudomonas aeruginosa (P. aeruginosa) is an opportunistic pathogen that is a leading cause of many types of infections both healthcare associated infections (HAIs) or community acquired infections. In general, this organism is highly resistant to different classes of antimicrobials through different mechanisms that represents a major concern in treatment of infections in hospitals. Aim of the study: To detect the association between the presence of MexA/MexB genes and the resistance pattern among P. aeruginosa. isolates from Ain Shams University Hospitals. Methods: A total of 60 isolates of P. aeruginosa were obtained from Main Microbiology Laboratory, Ain Shams University Hospitals. Phenotypic identification and antimicrobial susceptibility testing were performed followed by detection of MexA/MexB genes using polymerase chain reaction (PCR). Results: Most of isolates were isolated from urine samples 26 (43.3%), followed by sputum samples 14 (23.3%). Antimicrobial susceptibility showed highest maximum resistance to cefepime (97%), ceftazidime (90%), gentamycin (87%), Piperacillin (73%) and ciprofloxacin (60%). The least resistance was reported to meropenem (63%), imipenem (60%) and piperacillin/tazobactam (43%). 38 (63.3%) isolates were extensive drug resistance (XDR), 12 (20%) isolates were multi-drug resistance (MDR) and 10 (16.7%) isolates were non-MDR. MexA and mexB genes were detected in 56.7% (34 strains) and 46.7% (28 strains) of all tested isolates, respectively. According to our results, all strains that carry mexB gene carry MexA gene as well. Conclusion: Antimicrobial resistance among P. aeruginosa is widely spreading and significantly associated with presence of MexA/MexB gene.

Adhesively-bonded resin composites have the advantage of conserving sound tooth structure with the potential for tooth reinforcement, while at the same time providing an aesthetically acceptable restoration. However, no composite material has been able to meet both the functional needs of posterior restorations and the superior aesthetics required for anterior restoration. In an attempt to develop a dental resin composite that had the mechanical strength of hybrid composite materials and the superior polish and gloss retention associated with microfilled materials, nanofilled resin composites have been introduced in the market. Although nanofillers are the most popular fillers utilized in current visible light-activated dental resin composites and are claimed to be the solution for the most challenging material limitations as a universal restorative material, the mechanisms by which these fillers influence the resin composite properties are not well explained. In this study, some physical and mechanical properties of a nanofilled resin composite containing 60 vol. % zirconia and silica fillers were evaluated and compared to those of a microhybrid resin composite of the same composition. The nanofilled resin composite was found to have equivalent polymerization shrinkage and depth of cure to the microhybrid material but a slightly lower degree of conversion and density. Regarding mechanical behaviour, although the nanocomposite was found to exhibit significantly higher wear resistance, and equivalent flexural strength, its indentation modulus and nanohardness were slightly lower. Field-emission scanning electron microscopy (FE-SEM) analysis was conducted in order to evaluate the microstructure and to obtain a better understanding of the effect of the nanofillers on the behaviour of the nanocomposite.