Transcriptional levels of wzt in biofilm-forming Escherichia hermannii analyzed by quantitative real-time RT-PCR

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We have previously reported that clinical isolates of Escherichia hermannii (E. hermannii) from a persistent apical periodontitis lesion had the capacity to form biofilm containing mannose rich exopolysaccharide. We generated a biofilm-defective mutant strain 455 from E. hermannii strain YS-11 by random transposon insertion mutagenesis and demonstrated that a mutant lacking wzt (one of the ABC-transporter genes) was incapable of producing the viscous materials necessary for biofilm formation. In this study, we employed a quantitative real-time reverse transcription-polymerase chain reaction (RT-PCR) to learn how the transcriptional level of this gene fluctuates along with the growth of this organism. Strain YS-11 showed high transcriptional levels of wzt from the early exponential to the stationary phase of growth, and the peak was seen at 6hr of culture. When a plasmid pWZT carrying a wild type wzt ORF was introduced to strain 455, a recombinant strain designated as strain 455-LM showed denser meshwork structures around cells as well as higher transcriptional levels than those of the parent strain. These results may suggest that wzt is involved in the formation of E. hermannii biofilm.