In cystic fibrosis individuals, chronic lung infections and hospital-acquired pneumonia are caused by Pseudomonas aeruginosa. P. aeruginosa generates siderophores such as pyoverdine (PVD) as iron uptake systems to cover its needs of iron ions for growth and infection. lasR quorum sensing (QS) gene has a crucial function in PVD production and biofilm generation in P. aeruginosa. Fifty isolates of P. aeruginosa were obtained from clinical specimens of sputum (collected from individuals suffering from pulmonary infections). Antibiotic sensitivity test was performed for 50 P. aeruginosa isolates by using 10 antibiotics commonly used against P. aeruginosa and other Gram -ve bacteria. Ten MDR bacterial isolates, with the highest resistance (80-90%) against tested antibiotics, were further studied for virulence factors, such as biofilm formation, PVD production, and harbouring lasR QS gene. The 10 MDR isolates are able to create a biofilm, PVD producer, and contain lasR gene (the expected amplicon for the lasR gene is about 725 bp). The most potent isolate, PS31, was identified using 16S rRNA gene analysis to be P. aeruginosa PS31 (Accession number: LC619328.2.). Fresh and heated PVD produced by P. aeruginosa PS31 were injected in mice. The fresh PVD (0.3 mL; 37.4 µM), caused 100 % mortality within five days while 0.3 mL of heated PVD (toxoid), 15.3 µM, caused 50 % mortality.