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Background: Staphylococcus aureus, as a most important cause of nosocomial and community-acquired infections, shows resistance to a wide range of antibiotics. The aim of this study was the phenotypic and molecular study of clinical isolates of vancomycin-resistant Staphylococcus aureus isolated from hospitals in Rasht in a six- month period (February 2015 to July 95).
Materials and methods: 217 clinical samples were collected from different wards of hospitals in Rasht. Staphylococcus aureus isolates were identified by biochemical tests. To determine microbial resistance of the strains to antibiotic vancomycin, phenotypic tests of disk diffusion (according to the CLSI), and minimum Inhibitory concentration in microdilution broth method were used. Also, the presence of VanA gene, encoding resistance to the antibiotic vancomycin in separated isolate was evaluated by PCR method.
Results: 67 Staphylococcus aureus were identified. In the test determining resistance to the antibiotic by disk diffusion method, the results in terms of resistance rate against antibiotics was as follow: 10.5% chloramphenicol, 25.37% gentamicin, 37.32% tetracyclin, 38.80% vancomycin, 44.7% oxacillin and 100% penicillin. In the microdilution broth, 22.4% of the samples showed resistance to vancomycin. In PCR, no band was observed for genes VanA.
Conclusion: It is recommended that in molecular studies, the presence of genes VanA and VanB is assessed; since the resistance could be related to the presence of VanB gene.

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Background: One of the factors causing the resistance of Enterocus faecalis bacteria to the vancomycin antibiotic is the vanA gene, and the purpose of this research is to investigate the effect of silver nanoparticles on the expression of the vanC resistance gene.
Materials and methods: In this study, 98 isolates were examined after confirming the presence of the vanA gene and the antibiogram test of the treatment, the bacteria with multidrug resistance with the lowest ability to silver nanoparticles were performed and with the Real-time PCR technique, the data were analyzed. It was related to the change of gene expression. vanA was transformed in two analysis groups.
Results: Antibiotic resistance of the strains was 50% to vancomycin, 32% to ciprofloxacin, 15% to chloramphenicol, 5% to teicoplanin, 43% to erythromycin, 79% to amikacin, 80% to tetracycline, 80% to cephalexin, 85% to penicillin, and 1% to linozolid. Real-time analysis on the resistant strains in which the presence of vanA gene was confirmed by PCR and treated with silver nanoparticles showed that the effect of nanoparticles on the expression of vanA gene is significant.
Conclusion: Existing 87% of the multidrug resistance in 64 confirmed strains indicates that the issue of multidrug resistance is a serious warning in the use of antibiotics to treat infections caused by Enterococcus faecalis and the effectiveness of silver nanoparticles on vanA gene expression indicates that It can be used as an alternative to antibiotics in infections caused by Enterococcus faecalis.