Objective To investigate the influence of abaI expression on acinetobacter baumannii biofilm formation.Methods Acinetobacter baumannii strain S isolated from bums patients was collected for the study,while the standard strain ATCC19606 was served as the control.At 6,24 and 48 hours,the gene expressions of abaI,pgaA,pgaB and pgaC were detected by real-time fluorescent quantitative PT-PCR,secretion of N-acyl-homoserine lactones (AHLs) by biological sensor and biofilm formation by MTT method.Results (1) Gene expressions of abaI,pgaA,pgaB and pgaC at 6 hours were 8.63 ±5.93,1.98 ± 1.93,1.01 ± 1.32 and 2.67 ± 3.46 respectively,which showed a quick increase at 24 hours (22.81 ± 17.60,5.13 ± 4.32,5.66 ± 3.97,11.97 ± 7.75 respectively),followed by a rapid decline in 48 hours (3.43 ± 0.88,1.30 ± 0.24,3.01 ± 3.00,3.02 ± 3.29 respectively).Gene expressions of pgaB and pgaC at 6 hours and that of pgaA and pgaC at 48 hours revealed statistically significant differences from those at 24 hours (P ＜ 0.05).(2) AHLs showed a level of 18.49 ± 11.03 at 6 hours,reached a peak of 52.23 ± 15.95 at 24 hours,then descended to 5.53 ± 0.94 at 48 hours.AHLs level at 24 hours showed statistically significant difference from that at 6 hours and 48 hours (P ＜ 0.05).(3)Biofilm formation at 24 hours and 48 hours was 2.83 ±0.44 and 2.71 ±0.15 respectively,far higher than that at 6 hours (0.49 ± 0.11,P ＜ 0.05).(4) In the correlation analysis among AHLs,biofilm formation and gene abaI,pgaA,pgaB and pgaC expressions,significant positive correlation was found between abaI and pgaA and between AHLs and pgaC expression (P ＜ 0.05).Conclusion Acinetobacter baumannii may regulate gene expressions of pgaA and pgaC responsible for biofilm formation to adjust to the external environment by means of changing abaI gene expression and AHLs secretion.