Silver nanoparticles (AgNPs) are considered a good alternative for antibiotics due to emerging Multidrug Resistance (MDR) crisis. Resistance to AgNPs is approximately limited among Gram-positive and Gram-negative pathogens. Low toxicity to human cells permits its safe use as a new antimicrobial with broad spectrum. Bacterial cells are used as a factory for AgNPs synthesis supplying a powerful antimicrobial with eco-friendly way. In this study, MDR Escherichia coli strains were recovered from patients attending Minia University hospital. Biogenic synthesis of AgNPs was performed using E. coli cells. Transmission Electron Microscopy (TEM) was used to characterize AgNPs size and shape. Antibacterial activity of AgNPs was tested against the MDR E. coli isolates. Screening for Sil and Omp genes was done using polymerase chain reaction (PCR). A total of 13 MDR E. coli bacterial culture supernatant isolates were recovered from patients under study. Biosynthesis of AgNPs was observed after addition of supernatant to AgNO3 by color change from yellow to brown. TEM characterization indicated the presence of silver nanoparticles with 15-75 nm particle size range. Eleven of MDR E. coli isolates were sensitive to biogenic AgNPs under study. SilB and SilE genes were encoded by the two AgNPs-resistant E. coli isolates which were negative for OmpF and OmpC genes, respectively demonstrating the role of Sil efflux pump genes and porin deficiency in AgNPs resistance. As indicated, the emergence of silver resistance due to the wide spread of biocides including silver has become a great challenge for the treatment of different infections.
Key words: MDR Escherichia coli, SilB, SilE, silver resistance, OmpF, OmpC
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