BACTERIAL lung infections can be serious and life-threatening diseases in people of all ages. Recently, bacterial resistance to antibiotics has increased rapidly and the most serious concern is that some bacteria have become resistant to almost all of the easily available antibiotics.
The present work aimed to study the relation between some of the expressed virulence factors and antibiotic resistance among local Gram negative bacteria isolated from infected lungs of patients attended Tanta University hospital, Egypt. Out of 70 different clinical specimens, 30 Gram negative isolates were obtained; 46.6% and 53.3% of total isolates were Pseudomonas aeruginosa and Enterobacteriaceae, respectively. All bacterial isolates were tested for their susceptibility against 24 antimicrobial agents as well as the ability to express some virulence factors including hemolysin, gelatinase, protease, lipase, pigment and biofilm formation. The results showed the predominance of P. aeruginosa isolates resistance against many of the used antibiotics, with significantly higher mean percent of drug resistant (74.11±7.7) compared to that of Enterobacteriaceae (42.97±9.09). Also, all Pseudomonas isolates were extensively drug resistant (XDR), while Enterobacteriaceae were multi-drug resistance (MDR). Although, most virulence factors were expressed at higher rates in P. aeruginosa than other bacterial species, no relation between the studied virulence factors and antibiotic resistance except for biofilm production, as the results indicated a direct correlation between resistance of antibiotics and the production of biofilm from tested Gram negative bacteria. There was a significant association between biofilm formation and the extensivedrug resistant of Pseudomonas isolates compared to Enterobacteriaceae (P= 0.02).