Abstract:

Objective  To explore changes of expressions of efflux pump upstream regulatory genes adeS and adeR and corresponding functional gene cluster adeAB of  Acinetobacter baumannii (AB) isolates under free and biofilm formation conditions and investigate the effect of biofilm formation on the active efflux function and drug resistance. Methods  Nine drug-resistant and nine drug-sensitive AB strains isolated from wound excretion, blood, and venous catheter of burn patients hospitalized in Ruijin Hospital of Shanghai Jiao Tong University School of Medicine from March to September 2013 were collected. The strains were cultured for 24 h by tube method under shaking condition and the relative mRNA expressions of efflux pump gene adeA and adeB and regulatory genes adeS and adeR were detected by quantitative real-time PCR. Results  Expressions of adeA, adeB, adeS, and adeR of drug-resistant and drug-sensitive strains under free condition (free bacteria) were higher than those under biofilm formation condition (biofiim bacteria) (P<0.05). Expressions of adeA and adeB of drug-resistant strains under free and biofilm formation conditions were higher than those of sensitive strains (P<0.05). Conclusion  The active efflux function is a major mechanism of drug resistance of AB under free condition. After biofilm was formed, AB can down-regulate the expression of adeS by sensing the changes of biofilm condition, inactivating the adeR, and decreasing the expression of functional gene adeAB, which makes the biofilm being the leading cause for drug resistance.

Key words: burns, infection, Acinetobacter baumannii, biofilms, drug resistance, efflux pump gene