| Summary: | Abstract Background The context and purpose of the study: The spready dissemination of resistance mechanisms among extended spectrum beta-lactamases (ESBL) producing bacterial isolates has increasingly been reported. There is an urgent need to explore the antibacterial property of nontoxic biosafe compounds. This In-vitro experimental study aimed to evaluate the effect of silver nanoparticles (AgNPs) alone and in combination with ineffective antibiotics against ESBL producing isolates. Results Ciprofloxacin with AgNPs combination had the highest synergistic percentage against 91.43% of ESBL Escherichia coli isolates, and it was additive against 8.57% of them. As regards ESBL K. pneumoniae isolates, AgNPs with cefotaxime were synergistic against 75.00% of them, followed by ceftazidime and ciprofloxacin (62.50%). The least effective combination was ampicillin with AgNPs. The greatest enhancement of activity of the antibiotics was observed at silver minimum inhibitory concentration (MICAg) MICAg/2 and MICAg/4. At lower AgNPs concentrations, enhanced effects were less obvious. AgNPs inhibited the production of beta-lactamase enzymes in 91.43% of E. coli and 75% of Klebsiella pneumoniae isolates. Conclusion AgNPs are a valuable alternative to combat drug resistance, as they had synergistic effects when combined with different ineffective antibiotics against ESBL producing bacteria. AgNPs had lowered MIC values of antibiotics by several folds. Moreover, they inhibited the production of beta-lactamase enzymes.
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