| Pseudomonas aeruginosa brought more and more problems in the past century because of its intrinsic resistance to a variety of antimicrobial agents and its ability to develop multidrug resistance (MDR). Quinolones are of potent antibacterial activities against pathogenic bacteria and are used for the treatment of patients with the various infections. Ciprofloxacin has emerged as one of the most effective quinolones against P. aeruginosa. The intensive use of the antibiotic has led to the emergence of the resistance strain, which severely limited its usefulness.In this study, we collected 128 strains of P. aeruginosa in from clinic samples, and investigated the activity of the antipseudomonal such as norfloxacin, ofloxacin, ciprofloxacin, levofloxacin, ceftazidime, ceftriaxone, imipenem and Piperacillin. The main mechanisms of the resistance to quinolones of P. aeruginosa have been analyzed for mutations in the target genes and mutations in the regulatory gene for multidrug active efflux-pumps systems MexAB-OprM, we also assessed the roles of the mutation of gyrA and MexAB-OprM efflux-pumps systems in theresistance of the P. aeruginosa biofilm.All of the 128 strains of P. aeruginosa, the resistant rate to ceftriaxone, norfloxacin ciprofloxacin are 69.5%, 57.8% and 26.6%, respectively. 17 of 128 strains showed cross resistance to 4 drugs of quinlones; 13 of them displayed resistance to all antibiotics tested. Combination of ciprofloxacin or levofloxacin with Ceftazidime or piperacillin has the synergic effect , and the bactericidal activities to P. aeruginosa increased distinctively.The DNA sequence of the quinolone resistance-determining region (QRDR) of gyrA , gyrB, parC and parE genes , which coded type II topoisomerase, was analyzed with PCR and DNA sequencing in 20 clinical isolates of the ciprofloxacin-resistant P. aeruginosa. It was investigated that the correlation of type II topoisomerase mutation to drug resistance in resistances of P. aeruginosa. The mutation in typell topoisomerase genes was detected out for more than 90% ciprofloxacin-resistant isolates (18 of 20 strains). The mutation was found mainly in gyrA (18 strains) and parC (10 strains). 17 isolates possessed the mutation at the codon for 83 amino acid (ACC→ ATC) in gyrA. Only 2 resistant-isolates had the mutation in gyrB and parE, respectively. 2 resistant strains did not have any mutation in type II topoisomerase genes. Mutants in more than one gene of the typell topoisomerase genes disclosed the high level resistance to the antibiotics. 4 mutants of type II topoisomerase gene have the high-level multidrug resistance to antibiotics tested.The result of PCR product digested with enzyme SacII showed that the mutation, befallened at the location coded for 83 amino acid in QRDR of gyrA of the clinical isolates of P. aeruginosa, could be determined byrestriction fragment length polymorphism (RFLP) analysis.The accumulation of ciprofloxacin and effect of carbonyl cyanide m-chloro-phenylhydrazone (CCCP) on the accumulation were measured by fluorescene method in _P. aeruginosa. The steady-state accumulation concentration of ciprofloxacin was higher in the sensitive than that in the resistant of P. aeruginosa. The concentration of ciprofloxacin could be increased by adding CCCP in all tested strains in the cells, but obvious results were gotten from only multidrug resistance .oprM gene of the MexAB-OprM efflux was investigated by PCR, RT-PCR and sequencing in P. aeruginosa. No deletion or point mutilation in oprM gene was found in MDR or susceptible strains. The result of oprM gene expression measured by RT-PCR showed that the level of oprM gene expression was higher in MDR strains than that in other strains. High expression in oprM gene leads to MDR in clinical isolates of P. aeruginosaThe mexR gene is considered as a represser of MexAB-OprM operon. The DNA fragment of mexR gene was identified by PCR and sequencing. The point mutation at codon for 66 amino acid of the MexR was found in MDR clinical strains of P. aeru...
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