Abstract:ObjectiveTo evaluate the effect of azithromycin on class Ⅰ integronintegrase gene (intI1) mRNA expression in biofilmforming (BF) Pseudomonas aeruginosa(PA)．MethodsintI1 of 10 PA strains isolated from a hospital were detected, 1 strain with positive BF+intI1 was selected for culture, blank control group and three azithromycin trial groups (divided according to 3 concentrations:16 mg/L, 32 mg/L, and 64 mg/L) were set, experiments were repeated 5 times, expression of intI1 mRNA were detected by RTPCR． ResultsRelative expression of intI1 mRNA in azithromycin groups of 16 mg/L, 32 mg/L, 64 mg/L, and control group were （1.15±0.04）,（12.47±3.10）,（19.71±0.78）, and （1.00±0.00），respectively, there were significant difference among four groups（F=163.82，P＜0.001）；intI1 mRNA expression between 16mg/L azithromycin group and control group was not significantly different (P＞0.05), but among other groups were significantly different (P<0.05), intI1 mRNA expression in azithromycin groups increased with the enhancing concentration of azithromycin in culture solution .ConclusionExpression of intI1 gene mRNA in BF PA can be upregulated by the present of azithromycin，which may improve the probability of drugresistant genes, and promote drugresistant gene recombination.