Title: Deficiency in biofilm formation in Escherichia coli O157:H7 is not solely due to prophage insertion in mlrA Authors
Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: May 18, 2013
Publication Date: N/A
Technical Abstract: Background: Although a curli and biofilm expressing phenotype can be induced in Escherichia coli serotype O157:H7, strains examined under laboratory conditions are almost exclusively biofilm deficient and the reason for these deficiencies have remained elusive. CsgD, the central biofilm regulator, induces expression of the key biofilm components, curli fibers and cellulose. CsgD is highly regulated and requires both the RpoS sigma factor and its DNA-binding transcriptional activator, MlrA. In this study we test the unproven theory that phage insertions in mlrA are a major barrier to biofilm formation. Methods: Using 55 isolates of serotype O157:H7, we determined the prevalence of curli expression, biofilm formation, and prophage insertion in the mlrA gene. We then used complementation with a high-copy-number plasmid carrying mlrA to determine the effect of prophage insertion on both curli expression and biofilm formation. Results: Only 4 of the 55 strains showed affinity for Congo red, a curli-binding dye, and none of the strains formed significant biofilm. Prophage insertions were found in 53 of 55 strains. However, neither of the two strains with an intact mlrA formed biofilm. When plasmid pUC19::mlrA was transformed into the strains carrying a prophage in mlrA, only 15 strains showed increases in both CR affinity and biofilm formation. An additional 13 strains showed increases only in CR affinity, while 24 strains failed to express curli or biofilm. Conclusions: Although prophage insertions limit biofilm formation in some strains, additional barriers restrict biofilm and curli expression in the majority of serotype O157:H7 strains.