Probiotic Escherichia coli inhibits biofilm formation of pathogenic E. coli via extracellular activity of DegP Original paper

What was studied?

This study investigated how probiotic Escherichia coli Nissle 1917 inhibits biofilm formation by pathogenic E. coli during mixed community growth, with a focus on identifying the molecular mechanism responsible for this suppression. The authors examined whether inhibition depends on competitive growth, secreted metabolites, or protein factors, and they linked the activity directly to the extracellular function of the DegP protease. Because the focus keyphrase probiotic Escherichia coli DegP biofilm inhibition appears in this section, the analysis emphasizes how DegP secretion represents a functional microbiome signature that shapes interbacterial competition in multispecies environments.

Who was studied?

The experiments used the probiotic strain Escherichia coli Nissle 1917, a commensal E. coli control, and several clinically relevant pathogens, including enterohemorrhagic E. coli O157:H7, Staphylococcus aureus, Staphylococcus epidermidis, and Pseudomonas aeruginosa. These organisms were tested in single and dual-species biofilm models, with each population quantified by selective plating to track competitive interactions. The study also used isogenic EcN mutants lacking degP, hslU, or sat to identify the specific factor required for inhibition. This selection of strains allowed the authors to distinguish strain-specific effects, verify the necessity of DegP, and determine how probiotic–pathogen interactions unfold during biofilm development.

Most important findings

The study found that probiotic Escherichia coli DegP biofilm inhibition is driven by the extracellular secretion of DegP, a periplasmic protease that EcN uniquely exports outside the cell. EcN strongly reduced biofilm biomass of enterohemorrhagic E. coli, Staphylococcus aureus, and Staphylococcus epidermidis, while commensal E. coli did not display any inhibitory effect. The EcN supernatant alone decreased EHEC biofilms by nearly 1,000-fold, indicating that secreted factors, not direct contact, mediate the inhibition. Proteomic analysis identified more than fifty proteins unique to the EcN supernatant, but only DegP met the necessary molecular weight and functional requirements. Deleting degP abolished EcN’s ability to inhibit EHEC biofilms, while purified DegP directly repressed biofilm formation without affecting planktonic growth, demonstrating a targeted antibiofilm effect. DegP activity was selective, as it partially influenced S. epidermidis but did not suppress P. aeruginosa, suggesting that inhibition depends on the target’s surface properties and biofilm architecture.

Key implications

This work shows that probiotic Escherichia coli DegP biofilm inhibition represents a specialized ecological trait that shapes pathogen behavior in mixed microbiome settings, providing clinicians with mechanistic insight into how EcN reduces colonization by harmful bacteria. The selective activity of DegP highlights the possibility of identifying probiotic strains based on their secreted protein profiles rather than only their taxonomic identity. Because DegP suppresses biofilms without reducing planktonic growth, it may weaken pathogen persistence while minimizing selective pressure for resistance, which is valuable for therapeutic design. These findings also support the concept that probiotic activity depends on defined molecular signatures within the secretome, suggesting potential for engineered probiotics that enhance DegP secretion or combine synergistic antibiofilm factors. For clinical practice, recognizing that EcN carries unique functional properties may guide strain selection for preventing device-associated or gastrointestinal biofilm colonization.