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Published on: July 22, 2019
Interactions between commensal Enterococcus faecium and Enterococcus lactis and clinical isolates of Enterococcus
Theresa Maria Wagner1, Anna Kaarina Pöntinen2,3, Carolin Kornelia Fenzel1
1Research group for Host-Microbe Interactions, Department of Medical Biology, Faculty of Health Sciences, UiT The Arctic University of Norway, 9037 Tromsø, Norway.
Abstract:
Enterococcus faecium (Efm) is a versatile pathogen, responsible for multidrug-resistant infections, especially in hospitalized immunocompromised patients. Its population structure has been characterized by diverse clades (A1, A2, and B (reclassified as E. lactis (Ela)), adapted to different environments, and distinguished by their resistomes and virulomes. These features only partially explain the predominance of clade A1 strains in nosocomial infections. We investigated in vitro interaction of 50 clinical isolates (clade A1 Efm) against 75 commensal faecal isolates from healthy humans (25 clade A2 Efm and 50 Ela). Only 36% of the commensal isolates inhibited clinical isolates, while 76% of the clinical isolates inhibited commensal isolates. The most apparent overall differences in inhibition patterns were presented between clades. The inhibitory activity was mainly mediated by secreted, proteinaceous, heat-stable compounds, likely indicating an involvement of bacteriocins. A custom-made database targeting 76 Bacillota bacteriocins was used to reveal bacteriocins in the genomes. Our systematic screening of the interactions between nosocomial and commensal Efm and Ela on a large scale suggests that, in a clinical setting, nosocomial strains not only have an advantage over commensal strains due to their possession of AMR genes, virulence factors, and resilience but also inhibit the growth of commensal strains.
Insights
Clinical Enterococcus faecium strains, particularly clade A1, dominate nosocomial infections by inhibiting commensal strains. These pathogens possess antimicrobial resistance and virulence factors, giving them a competitive edge.
Area of Science:
- Microbiology
- Infectious Diseases
- Bacteriology
Background:
- Enterococcus faecium (Efm) is a significant cause of multidrug-resistant infections in vulnerable patients.
- Efm exists in distinct clades (A1, A2, and E. lactis), each with unique adaptations, resistomes, and virulomes.
- The ecological advantage of dominant nosocomial Efm clade A1 strains remains incompletely understood.
Purpose of the Study:
- To investigate the in vitro interactions between clinical Efm clade A1 strains and commensal Efm (clade A2) and E. lactis (Ela) isolates.
- To identify mechanisms underlying the competitive interactions between these Enterococcus strains.
- To understand the role of bacteriocins in Enterococcus inter-clade competition.
Main Methods:
- In vitro co-culture experiments involving 50 clinical Efm isolates and 75 commensal isolates (25 Efm, 50 Ela).
- Assessment of growth inhibition patterns between clinical and commensal strains.
- Genomic analysis using a custom database to identify bacteriocins produced by the isolates.
Main Results:
- Clinical Efm clade A1 strains demonstrated significantly higher inhibitory activity against commensal strains (76%) compared to vice versa (36%).
- Inhibitory activity was primarily mediated by heat-stable, proteinaceous compounds, suggesting bacteriocin involvement.
- Genomic screening confirmed the presence of bacteriocins, highlighting their role in inter-clade competition.
Conclusions:
- Nosocomial Efm clade A1 strains possess a competitive advantage over commensal strains, partly due to their ability to inhibit commensal growth.
- Bacteriocins likely play a crucial role in the ecological dominance of clinical Efm strains in hospital environments.
- Understanding these interactions is vital for managing multidrug-resistant Enterococcus infections.
