AUTHOR=Andreozzi Elisa , Gunther Nereus W. , Reichenberger Erin R. , Rotundo Luca , Cottrell Bryan J. , Nuñez Alberto , Uhlich Gaylen A. 

TITLE=Pch Genes Control Biofilm and Cell Adhesion in a Clinical Serotype O157:H7 Isolate

JOURNAL=Frontiers in Microbiology

VOLUME=9

YEAR=2018

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2018.02829

DOI=10.3389/fmicb.2018.02829

ISSN=1664-302X

ABSTRACT=<p>In a previous study, induction of the <italic>Escherichia coli</italic> serotype O157:H7 SOS response decreased <italic>csgD</italic> expression in the clinical isolate PA20 at 30°C but strongly induced genes in the horizontally transferred-DNA regions (HTR), including many known virulence regulators. To determine the role of HTR regulators in the control of <italic>csgD</italic> and curli, specific regulators were plasmid-expressed in the wild-type and mutant strains of PA20 and its biofilm-forming derivative, 20R2R. At 30°C, plasmid over-expression of the O157:H7 group 3 <italic>perC</italic> homolog, <italic>pchE</italic>, strongly repressed PA20 <italic>csgD</italic> transcription (&gt;7-fold) while the group 1 homologs, <italic>pchA</italic> and <italic>pchB</italic>, resulted in smaller reductions (&lt;2.5-fold). However, SOS induction decreased rather than increased <italic>pchE</italic> expression (&gt;6-fold) making group 1 <italic>pch</italic>, which are enhanced by the SOS response, the likely SOS-induced <italic>csgD</italic> repressors. Plasmid-based <italic>pchE</italic> over-expression also reduced 20R2R biofilm formation (&gt;6-fold) and the curli-dependent, Congo red affinity of both PA20 and 20R2R. However, to properly appreciate the regulatory direction, expression patterns, and environmental consequences of these and other CsgD-controlled functions, a better understanding of natural <italic>pchE</italic> regulation will be required. The effects of HTR regulators on PA20 and 20R2R adhesion to HEp-2 cell at host temperature were also studied. Under conditions where prophage genes were not induced, curli, rather than <italic>espA</italic>, contributed to host cell adhesion in strain 20R2R. High levels of <italic>pchE</italic> expression in trans reduced curli-dependent cell adherence (&gt;2-fold) to both 20R2R and the clinical isolate PA20, providing a host-adapting adhesion control mechanism. Expression of <italic>pchE</italic> was also repressed by induction of the SOS response at 37°C, providing a mechanism by which curli expression might complement EspA-dependent intimate adhesion initiated by the group1 <italic>pch</italic> homologs. This study has increased our understanding of the O157 <italic>pch</italic> genes at both host and environment temperatures, identifying <italic>pchE</italic> as a strong regulator of <italic>csgD</italic> and CsgD-dependent properties.</p>