环丙沙星对培养的铜绿假单孢菌释放DNA的影响

Release of DNA from Pseudomona aeruginosa in vitro during spontaneous growth and treatment with ciprofloxacin

目的观察不同浓度的环丙沙星对培养的铜绿假单孢菌释放DNA的影响.方法选择体外对铜绿假单孢菌1244株(ATCC 27317)敏感的环丙沙星为实验所用的抗生素, 检测其最小最小抑菌浓度(MIC)和最小杀菌浓度(MBC);将不同稀释度(32～0.03 mg/L)的环丙沙星与该菌株菌液在37℃培养,分别取其培养4 h和24 h的上清液经DNA电泳法检测其细菌DNA释放的情况.结果无论有无环丙沙星,DNA电泳法均未见到培养4 h 的样本存在细菌释放的游离DNA.体外培养24 h,铜绿假单孢菌可自发释放一定量的游离DNA分子,呈两个明显的区带, 其分子量分别大于2000 bp和小于100 bp;远低于MIC的环丙沙星可诱导铜绿假单孢菌释放更多的游离DNA, 分布在3个明显的区带,其中两个区带大于2000 bp,另1个区带小于100 bp;大于或等于MIC的环丙沙星对铜绿假单孢菌无诱导DNA释放的作用.结论自然生长情况下铜绿假单孢菌就可自发释放一定量的游离DNA分子;低于MIC的环丙沙星存在使这一现象更加明显,而且铜绿假单孢菌释放游离DNA分子的多少和分子量大小均有明显的差别.

Objective To observe the DNA release from Pseudomonas aeruginosa (P. aeruginosa) during spontaneous growth and exposure to different concentrations of ciprofloxacin (Cipro) in vitro. Methods The P. aeruginosa 1244 strain (ATCC 27317) was selected because it was sensitive to Cipro in vitro. The minimal inhibitory concentration (MIC) and minimal bactericidal concentration (MBC) of Cipro against this strain were determined, respectively. Different concentrations of Cipro were cultured with this strain at 37℃ for 4 h and 24 h. The samples of culture supernatant were filtered and electrophoresed in 1.8% agarose with SYBR Gold stain. Then the images of the gel sheets were photographed. Results The MIC and MBC of Cipro were 0.25-0.5 mg/L. The free bacterial DNA in 4 h culture samples with or without Cipro could not be detected by this method. The certain amount of free bacterial DNA molecules in 24 h culture samples without antibiotic appeared at the two zones whose molecular weights were more than 2000 bp and less than 100 bp. The large amount of free bacterial DNA molecules showed at three zones in 24 h culture samples with Cipro when its concentrations were much lower than its MIC. In terms of DNA molecular weight, the first two zones were above 2000 bp, and the third zone was below 100 bp. There was no detectable DNA release from bacteria in 24 h culture samples when Cipro was at or above its MIC. Conclusions The certain amount of bacterial DNA were released from P. aeruginosa in the spontaneous growth. Different concentrations of Cipro had quite differential effects on the DNA release from P. aeruginosa in quantities and molecular weights in vitro.