ABSTRACT
One hundred and twelve Pseudomonas aeruginosa strains were isolated from 436 different clinical specimens collected from patients attending different hospitals in El-Minia governorate. Antibiotics susceptibility patterns of the isolated Ps. aeruginosa isolates to quinolones were studied and results revealed higher percentage of resistance ranged from 22.32% to 75%. gatifloxacin was the most active quinolone against the tested isolates as the percentage of resistance was 22.32% while nalidixic acid was the least active one as the percentage of resistance was 75%. The percentage of resistance to ciprofloxacin, levofloxacin and ofloxacin was 41.96%, 47.32% and 49.1% respectively. Co - resistance to other chemically unrelated antibiotics was also studied and the result showed that, more than 90% of the tested Ps. aeruginosa isolates were resistant to amoxycillin, chlormphenicol and tetracyline. On the other hand, variable levels of resistance were obtained for gentamicin, azithromycin, cefoperazone and cefotaxime. Interestingly, all the tested Ps. aeruginosa isolates were 100% sensitive to amikacin. Ps. aeruginosa isolates showed multiple drug resistance patterns to quinolones and other antibiotics were selected to study the possible mechanisms of resistance to quinolones. Efflux mechanisms was studied flourometerically and the results revealed presence of active efflux pumps in the tested isolates as indicated by the increase in the fluorescence of N-phenyl-1-Naphthylamine [NPN] after preincubation of the cells with the efflux inhibitor carbonyl cyanide m-chlorophenylhydrazone [CCCP]. Also, examination of outer membrane proteins in the tested isolates revealed over production of outer membrane proteins of an apparent molecular mass of 50 KDa and 54 KDa suggesting the role of these proteins in quinolones resistance. In addition to the absence of outer membrane protein of molecular mass 46 KDa which aids the intake of the quinolones into the bacterial cells. In conclusion, quinolones resistance in Ps. aeruginosa were associated with multidrug efflux pumps and alteration in the outer membrane proteins