The current study intended to illustrate the influence of stress exposure (oxidative stress and osmotic stress) on the susceptibility of P. aeruginosa to antibiotics. Furthermore, the impact of both oxidative and osmotic stresses on P. aeruginosapathogenesis was also studied using murine infection model. Treatment of P. aeruginosa infections is highly difficult due to the higher bacterial resistance to usually used antimicrobial agents. Consequently, the findings of this study could expand our familiarity with P. aeruginosa and so help us to control infections caused by this opportunistic microorganism. In the present study, a total of 100P.aeruginosa isolates were recovered from 300 specimens during theperiod from November 2017 to May2018 from patients with wound infections, urinary tract infections, burn infections, respiratory tract infections, ear and eye infection admitted to the El-Ahrar Educational Hospital and Zagazig university hospital ,Zagazig, Sharkia, Egypt. Antibiotics susceptibility testing was doneby the standard disc diffusion method against all the isolates. P. aeruginosa isolates in this study showed the highest resistance against fluroqinolones (ciprofloxacin, Gatifloxacin (63% each), gentamycin (62%), followed by carbapenem (meropenem; 60%). Conversely, the highest susceptibility was obtained against colistin sulfate (93%). In addition, the antimicrobial susceptibility testing revealed that 53% of P.aeruginosaisolates in this study were MDR. The most sensitive and the most resistant isolates in this study in addition to standared strain p.aeruginosa PAO1 were selected for further investigation. First, the antibiotic susceptibility of P. aeruginosa clinical isolates of recovered from different sources such as urinary tract infection, respiratory tract infection, wound and eye infection in addition to standard strain P. aeruginosa PAO1 was tested prior and following exposure to H2O2 and NaCl stress The experiment conditions were optimized in order to achieve the required stressful environment without drastically affecting bacterial survival. Oxidative stress impact on bacterial cells was conducted using 3.5 mM H2O2 and the ideal osmotic stress condition was 4% NaCl that offer required stress environment without adversely affecting bacterial survival. Importantly, exposure of P. aeruginosato oxidative stressby H2O2 or osmotic stress by NaClsignificantly affected bacterial susceptibility to tested antibiotics (colistin,ceftazedime,tobramycin and ciprofloxacin) when compared with unstressed bacteria. In addition to determining the influence of stress exposure on Pseudomonas susceptibility to antibiotics, the contribution of oxidative and osmotic stress to bacterial virulence was determined. The expression levels of QS genes;lasI, lasR, rhlI, rhlR, pqsR and pqsA, that regulate production of P. aeruginosa virulence factors, were determined in both unstressed, H2O2-stressed and NaCl-stressedP. aeruginosausing qRT-PCR. The transcript levels of QS genes were significantly higher in unstressed P. aeruginosacompared with H2O2- and NaCl-stressed cells. Additionally, the effect of oxidative and osmotic stress to P. aeruginosa pathogenesis was further investigated using mice infection model. Both mice survival and body weight were followed up over 4-days time peroid. Furthermore, the weights of mice organs (spleen, liver and kidney) were determined for mice infected with H2O2-stressed, NaCl-stressed and compared with those of mice infected with unstressed bacteria. In current study,the survival rate of mice infected with stressed P. aeruginosa was higher relative to those infected with unstressed bacteria. In addition, body weight of mice infected with unstressed P. aeruginosa was lower than that of mice inoculated with stressed bacteria. Remarkably, organ samples obtained from mice infected with unstressed bacteria showed a significant increase in bacterial load and NaCl bacteria. In conclusion, the current study highlights the influence of stress exposure on P. aeruginosa both antibiotic susceptibility and host pathogenesis. P. aeruginosa sensitivity to commonly used antibiotics was found to significantly alter upon exposure to oxidative and osmotic stress. This finding shed light on the importance of environmental conditions in reshaping bacterial response to antimicrobial agents. More attention should be paid to patients suffering from Pseudomonas infections both during treatment by antibiotics and bacterial control using disinfectants and/or antiseptics.