Proximity-dependent inhibition in Escherichia coli isolates from cattle

Area of Science:

• Microbiology
• Bacterial interactions
• Population dynamics

Background:

• Bacteria engage in complex interactions influencing population dynamics.
• Understanding inter-bacterial communication and competition is crucial for microbial ecology.
• Escherichia coli (E. coli) serves as a model organism for studying bacterial behavior.

Purpose of the Study:

• To describe a novel proximity-dependent inhibition (PDI) phenotype in Escherichia coli.
• To investigate the conditions and mechanisms underlying PDI.
• To assess the effectiveness of PDI against various E. coli strains.

Main Methods:

• Coculturing of distinct E. coli inhibitor and target strains in defined minimal media.
• Monitoring bacterial population changes (CFU/ml) during growth transitions.
• Assessing the role of conditioned media and physical separation (0.4-μm filter) in PDI.
• Testing PDI against diverse E. coli strains, including pathogenic and commensal types.

Main Results:

• Target E. coli populations rapidly declined (>4 log CFU/ml) within 2 hours when cocultured with inhibitor strains near stationary phase.
• Inhibition was dependent on close proximity; conditioned media or physically separated cultures did not induce significant target strain decline.
• No evidence of lytic phage was found; extracellular bacteriocin activity was unlikely unless localized.
• PDI was effective against a broad range of E. coli, including E. coli O157:H7, enterotoxigenic strains, and multidrug-resistant strains.
• Coculture of two inhibitor strains resulted in mutual immunity.

Conclusions:

• Proximity-dependent inhibition is a novel bacterial phenotype in E. coli.
• This mechanism allows bacteria to gain a numerical advantage during the transition to stationary phase.
• PDI contributes to bacterial competition and may confer a competitive edge when growth conditions improve.