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J Infect Chemother. 2013 Feb;19(1):77-81. doi: 10.1007/s10156-012-0455-y. Epub 2012 Jul 21.

gyrA and parC mutations in quinolone-resistant clinical isolates of Pseudomonas aeruginosa from Nini Hospital in north Lebanon.

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Medical Microbiology Laboratory, Azm Center for Research in Biotechnology and Its Applications, Doctoral School of Sciences and Technology, Lebanese University, Tripoli, Lebanon.


The problem of Pseudomonas aeruginosa resistance to fluoroquinolones is of growing concern in hospitals. The major mechanism of the resistance of this bacterium to fluoroquinolones is the modification of type II topoisomerases (DNA gyrase and topoisomerase IV). In this study, we examined, using the technique of DNA pyrosequencing, mutations in the quinolone resistance-determining regions of the gyrA and parC genes of 38 clinical isolates of P. aeruginosa that were non-susceptible to at least one of the three fluoroquinolones tested. The most common origin of the isolates was sputum (44.7 %), followed by wounds (11 %), urine (5 %), and ear discharge (5 %). Serotypes O:11 (21 %), O:2 (18.4 %), and O:6 (7.8 %), were the most predominant. Among these 38 isolates, 11 were susceptible, 22 were resistant, and 5 were intermediate-resistant to ciprofloxacin. We found that 19 (50 %) of these strains had a mutation in the gyrA gene (Thr 83 Ile), one of them presented a new mutation (His 80 Arg), 8 (21.05 %) strains had an additional mutation in the parC gene (Ser 80 Leu), and one of these strains had two new mutations not previously reported (Gln 84 Asp, Ala 85 Gly). The ciprofloxacin-sensitive strains had no mutations in the sequence area examined. We found that 81.8 % of the isolates that were resistant to ciprofloxacin had a mutation in the gyrA gene. Some of these resistant strains also had a mutation in the parC gene. The results of this study suggest that pyrosequencing is a reliable technique for the determination of the antibiotic resistance pattern of a given bacterial strain.

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