[Quantification of class 1 integrase gene expression of Pseudomonas aeruginosa in biofilm]

To study the molecular mechanism of integron related gene transfer in biofilm and aqueous culture of P. aeruginosa by investigating the expression level of intI1 mRNA in class 1 integron positive strains.

A competitive reverse transcription-PCR (cRT-PCR) method was designed to quantify class 1 integrase mRNA production in two clinical P. aeruginosa strains called PA10 and PA39 when they were grown in biofilms and planktonic culture. In brief, competitive DNA (cDNA) was obtained via PCR from the genomic DNA of class 1 integron positive strains. Then the competitive RNA (cRNA) was amplified from the cDNA. Finally the serials diluted cRNA were mixed separately with the total RNA extracted from the biofilm and planktonic culture of P. aeruginosa and the competitive RT-PCR were conducted. After electrophoresis, the expression level of intI1 mRNA was quantified by comparing with the amount of the cDNA.

The PA10 and PA39 strains produced intI1 mRNA both in their biofilms and planktonic cells. Furthermore the expression levels of intI1 mRNA from the two strains were of approximation in their biofilm and plankton stage respectitively, while the quantities of intI1 mRNA expression in their biofilm stage were about 15 times higher than those in their planktonic stage.

The integrase gene is up-regulated at mRNA level in P. aeruginosa biofilm, which may be one of the reseans for the spread of antibiotic resistance and the formation of multidrug resistance.