الفهرس 
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Abstract
In the present study, The present work aimed to study the anti-quorum sensing activity of sub-inhibitory concentrations of some compounds and their effects on the virulence of P. aeruginosa PAO1. These compounds included some antibiotics such as: β-lactam antibiotics (ceftazidime, cefepime, and imipenem), aminoglycosides (amikacin and gentamicin), and ciprofloxacin, as well as other pharmaceutical preparations like: aspirin, and ascorbic acid (vitamin C). These drugs were investigated for their effect on quorum sensing signals (AHLs) and on virulence factors production including: lasB elastase, total protease, hemolysin, pyocyanin, motility, and biofilm formation. Furthermore, we explored the effect of sub-inhibitory concentrations of both aspirin and vitamin C on the expression of some genes encoding the quorum sensing cascade (such as: lasI, lasR, pqsA, pqsR, rhlI, and rhlR genes) and genes regulating type II and type III secretion systems like; lasB, toxA, exoS and exoY genes in P. aeruginosa PAO1 using RT-PCR technique. Screening the anti-quorum sensing activity of sub-inhibitory concentrations of those compounds demonstrated significant reduction in QS and related virulence factors, suggesting the possible implication in controlling P. aeruginosa infections.