Interspecies interactions in mixed-species biofilms formed by Enterococcus faecalis and gram-negative bacteria isolated from polymicrobial diabetic foot ulcers

Abstract

Diabetic foot ulcers (DFU) are exacerbated by bacterial colonisation. Here, a high prevalence of Enterococcus faecalis was observed in DFU patients from an Argentinean hospital. E. faecalis was frequently co-isolated with Escherichia coli, Morganella morganii, and Pseudomonas aeruginosa. The effect of interspecies interactions on bacterial growth was investigated in mixed-species macrocolony biofilms developed in Lubbock-Glc-agar. Similar cell counts were found for E. faecalis and M. morganii growing in mixed and single-species biofilms. An E. faecalis strain showed 1 Log higher cell counts in mixed biofilms with E. coli. Remarkably, E. faecalis strains showed 2 to 4 Log higher cell counts in mixed biofilms with P. aeruginosa. This effect was not observed in planktonic growth or biofilms developed in tryptic soy agar. The present findings reveal bacterial interactions that benefit E. faecalis in mixed-species biofilms, mainly with P. aeruginosa, in a medium that partially mimics the nutrients found in DFU.

Keywords:

• Diabetic foot ulcer
• polymicrobial infection
• mixed-species biofilm
• Enterococcus faecalis
• Escherichia coli
• Pseudomonas aeruginosa

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was supported by PICT grant number 2017-0183 from Agencia Nacional de Promocion Cientifica y Tecnologica, Argentina, to EMG; and intramural funding from Fundacion Cientifica Felipe Fiorellino, Universidad Maimonides, Argentina, to EMG. FM is a doctoral fellow and EMG is a researcher member of CONICET. The authors would like to thank Dr. Carol Davies-Salas for a thorough language revision of the manuscript.