H-036. Evaluation of the Effects of Quorum-Sensing Signaling Pathways on the Expression of hha and other Regulators of LEE Expression in Escherichia coli O157:H7

V. K. Sharma1, S. M. D. Bearson1, B. L. Bearson2;
1USDA,/ARS, Natl. Animal Disease Ctr., Ames, IA, 2USDA/ARS, Natl. Soil Tilth Lab., Ames, IA.

Enterohemorrhagic Escherichia coli (EHEC) O157:H7 is an emerging food-borne pathogen causing diarrhea, hemorrhagic colitis (HC), and hemolytic-uremic syndrome (HUS) in humans. EHEC O157:H7 produces characteristic attaching-and-effacing (A/E) lesions. The genes required for the formation of A/E lesions are encoded by the locus of enterocyte effacement (LEE), whose expression is regulated by the LEE-encoded positive regulator Ler. In addition to Ler, various other positive (GrlA, IHF, Fis, QseA, and QseD) and negative regulators (GrlR, Hha, and H-NS) affect LEE expression. Since quorum-sensing signaling pathways have been shown to up-regulate LEE expression through QseA and QseD, we were interested in comparing levels of other positive and negative regulators in EHEC O157:H7 that was deleted of gene or genes encoding quorum-sensing signaling pathways. We have previously reported that Hha exerts a negative effect on the transcription of LEE-encoded genes by down-regulating transcription of ler. In order to understand whether quorum-sensing facilitated increased expression of LEE by modulating transcription of hha, a qseC mutant of EHEC O157:H7 strain 86-24 was constructed by deleting the qseC gene of the qseBC operon (encodes a two-component quorum-sensing signal transduction system). Reverse transcription-PCR (RT-PCR) analysis of the RNA prepared from a wild-type and a qseC mutant strain showed no significant affect on the transcription of hha in qseC mutant relative to the wild-type strain. Similarly, transcriptional levels of ler and ler-regulated espA were almost identical between the parent and qseC mutant strains. These results suggest that although the quorum-sensing signaling pathway encoded by the qseBC operon does not relieve Hha-mediated repression of ler in order to induce expression of espA, the role of signaling pathways encoded by qseEF and sdiA in determining the hierarchy of hha among the regulators impacting LEE expression needs further investigation.