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PurposeTo investigate the main molecular resistance mechanisms to fluoroquinolones (FQs) in Pseudomonas aeruginosa and also to investigate the effect of time and concentration on mutations in resistance genes.Materials and methodsThe clinical isolates of P. aeruginosa which are sensitive to ciprofloxacin (CIP) or levofloxacin (LEV) were collected. The isolates were incubated with different concentrations of CIP or LEV for 5 days and the minimal inhibitory concentrations (MICs) of CIP, LEV and ofloxacin (OFX) were measured. The MIC of FQs to P. aeruginosa was measured by the agar dilution method. FQ resistance determining regions of gyrA, gyrB, parC and parE were amplified by PCR, and mutations in four genes were explored using sequence analysis with the Snapgene software. The relative expression levels of two efflux pumps genes (mexA and mexE) were measured by quantitative reverse transcription PCR.ResultsA total of eleven isolates were collected from the Second Hospital of Shanxi Medical University. Amino acid alterations in gyrA and gyrB were mainly detected in resistant mutants, and the percentage of strains with amino acid alterations in gyrB was significantly higher than that in gyrA (P<0.001). MICs of strains with mutations both in gyrA and gyrB were not significantly higher than those of strains with mutations only in gyrB (P>0.05). No amino acid alterations were detected in genes of parC and parE. In both gyrA and gyrB, the number of amino acid alterations increased with incubation time prolonged and increased with increasing incubation concentration.ConclusionCIP was more competent than LEV in making P. aeruginosa resistant to in vitro selection. Mutations occurring in gyrB played an important role in FQ resistance of P. aeruginosa in vitro selection.

A new bacteria-based sensor for determination of glycerol was reported, in which mutant bacteria induced from the strain of Bacillus subtilis AS1.398 was used as a biocatalyst. The calibration graph of the proposed sensor was linear in the range of 1-10% (w/v) glycerol and the correlation coefficient was 0.9946. Lifetime of the sensor was more than two weeks. There was no significant interference from substances commonly coexisting in the fermentation broth except acetic acid. The sensor would be useful for monitoring glycerol during fermentation due to its linearity, selectivity, and lifetime. The bacteria could be used as a catalytic enzyme membrane which can reproduce itself in proper matrix.

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