Transcriptional Levels of wzt of Biofilm-Forming Escherichia hermannii

Previously, we reported that Escherichia hermannii strain YS11, an oral isolate that forms biofilms, can cause persistent infections despite the lack of detectable virulent factors. Its mutant, strain 455, which possessed a mutated (by transposon) wzt loci, lost its ability to produce viscous material, form cell surface-associated meshwork-like structures, and biofilms. Objectives: To examine the transcriptional level of wzt of biofilm-positive and –negative strains and to evaluate whether wzt was inducible in the test strains. Methods: RNA samples were extracted from cultures of strains YS11, YS11-455, and YS11-455-LM. Strain YS11-455-LM contained a vector carrying an intact wzt with a lac Z promoter. Transcriptional levels of wzt were analyzed by real time reverse transcription (RT)-PCR. Results: We measured the relative changes in RNA expression of wzt following induction with isopropyl-ß-D-1-thiogalactopyranoside (IPTG) in the test organisms. Treatment with IPTG resulted in a high level induction of the lacZ operon and expression of cell surface-associated meshwork structures. Conclusion: The increase in transcriptional levels of wzt corresponds to the expression of the cell surface-associated meshwork structures in the test organisms. It is plausible that wzt is involved in the transport or assembly of exopolysaccharides that is necessary for biofilm formation.