570株铜绿假单胞菌对11种抗菌药物的敏感性及其耐氟喹诺酮机制

目的　了解铜绿假单胞菌的耐药性及其耐氟喹诺酮的机制。方法　Kirby Bauer琼脂扩散法测定 5 70株铜绿假单胞菌对 11种抗菌药物的敏感性 ,琼脂稀释法测定其中 111株对两种氟喹诺酮的最低抑菌浓度 (MIC)。直接序列分析和聚合酶链反应 限制性长度多态性 (PCR RFLP)分析环丙沙星耐药菌株gyrA和parC基因突变。结果　 5 70株铜绿假单胞菌对头孢吡肟、亚胺培南、阿米卡星和头孢他啶的敏感性较高 ,其耐药率分别为 10 9%、11 1%、11 8%、12 5 %。环丙沙星、头孢哌酮 /舒巴坦和哌拉西林的耐药率分别为 2 9 2 %、2 3 5 %和 33 7%。耐环丙沙星和ICU临床分离的菌株对所测试的抗菌药物的耐药率均较高 ,6 0 %以上为多重耐药 (MDR)菌株。 80株耐环丙沙星菌株中 6 6株( 75 % )出现gyrA基因Thr83(ACC)→Ile(ATC)突变 ,5 2株 ( 6 5 % )发生parC基因Ser87(TCG)→Leu(TTG)突变 ,同时存在上述两种突变的有 5 2株 ( 6 5 % ) ,而 31株环丙沙星敏感菌中未发现上述突变。gyrA和parC双基因突变对环丙沙星的MIC显著高于单独gyrA基因突变株和不存在上述突变的菌株 ,P <0 0 5。结论　铜绿假单胞菌的耐药性日趋严重 ,特别是耐环丙沙星和ICU分离株对多种抗菌药物耐药 ;氟喹诺酮类药物作用靶位gyrA和parC的基因突变是临床分离铜绿假单

Susceptibility of 570 Pseudomonas aeruginosa strains to 11 antimicrobial agents and the mechanism of its resistance to fluoroquinolones

OBJECTIVE: To investigate the resistance of Pseudomonas aeruginosa (P. aeruginosa) to 11 antimicrobial agents and the mechanism of its resistance to fluoroquinolones (FQs). METHODS: The susceptibility of 570 strains of P. aeruginosa isolated clinically to 11 antimicrobial agents were detected by Kirby-Bauer disc diffusion method. The minimal inhibitory concentration (MIC) of 111 strains thereof to two FQs was determined by agar dilution method. 80 strains resistant to ciprofloxacin (MIC >or= 4 mg/L) were studied for the presence of point mutations in the gyrA and parC gene by direct sequencing and polymerase chain reaction-restriction fragment length polymorphisms (PCR-RFLP) method. RESULTS: The resistance rates of P. aeruginosa to cefepine, imipenem, amikacin, and ceftazidine, and aztreonam were 10.9%, 11.1%, 11.8%, 12.5%, and 16.6% respectively. The resistance rates to ciprofloxacin, levofloxacin, cefoperazone/sulbactam, and piperacillin were 29.2%, 32.9%, 23.5% and 33.7% respectively. The resistance rates to gentamycin and cefotaxime were 35.7% and 41.1% respectively. More than 60% of the ciprofloxacin resistant strains and the intensive care units (ICU) isolates were multidrug resistant. Among the 80 ciprofloxacin resistant strains, 66 (75%) had a mutation in gyrA codon: Thr83 (ACC)-->Ile (ATC), 52 strains (65%) had a mutation at parC codon: Ser87 (TCG)-->Leu (TTG), and 52 strains (65%) had both the above mentioned gyrA and parC mutations; while gyrA or parC mutation was not observed in the 31 ciprofloxacin susceptible strains. The MIC of ciprofloxacin for the 52 strains with mutations in both gyrA and parC genes was 19.80 mg/L +/- 2.11 mg/L, significantly higher than those for the 14 strains with mutation only in gyrA gene (11.88 mg/L +/- 2.73 mg/L, P < 0.05) and the 143 strains without gyrA and parC gene mutants (11.89 mg/L +/- 2.12 mg/L, P < 0.05). CONCLUSION: Resistance to antimicrobial agents of P. aeruginosa strains remains a problem. In particular, those ciprofloxacin resistant strains and ICU isolates are resistant to most of the antimicrobial agents. The resistance to fluoroquinolones of the clinical isolates of P. aeruginosa is mainly due to the mutations in gyrA and parC genes encoding the target enzyme of fluoroquinolones.