OBJECTIVETo observe the DNA release from Pseudomonas aeruginosa (P. aeruginosa) during spontaneous growth and exposure to different concentrations of ciprofloxacin (Cipro) in vitro.

METHODSThe 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 degrees C 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.

RESULTSThe 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.

CONCLUSIONSThe 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.