Nowadays, due to their potential application as probiotics for humans or animals, many beneficial lactic acid bacteria have been isolated from different natural environments. These include members of the genus Enterococcus - quite specific due to their ambiguous nature, varying from pathogens to probiotics. In our work we present a whole-genome sequencing (WGS)-based approach for assessing the potential of bacteriocin-producing Enterococcus isolates from beehives to serve as natural preserving agents against bacterial infections associated with honeybees. Potential Enterococcus spp. isolates from pollen granules were tested with the well diffusion assay for bacteriocin activity against Paenibacillus larvae, the causative agent of the American foulbrood disease (AFB). Two of them gave positive results and were determined at species level by 16S rRNA genes sequencing. They were then subjected to WGS using the Illumina HiSeq platform. The resulting raw data reads were processed and further analyzed by using only freely available web-based tools (the Shovill pipeline, QUAST, BAGEL4, ResFinder, VirulenceFinder and PlasmidFinder). The analysis revealed that both of them represent clonally identical isolates of the same strain. This specific strain was named Enterococcus faecium EFD, and was genotyped by the MLST-2.0 Server. Five bacteriocin genes were found in the assembled genome, providing a possible explanation for the antimicrobial properties of the isolate. The protein nature of the inhibitory agent/s was confirmed by treatment with proteinase K. No resistance determinants for clinically important antibiotics and functional virulence factor genes were detected. The bioinformatic analyses of the draft genome sequence suggest that E. faecium EFD is not pathogenic.The observation that E. faecium EFD was present within more than one of the beehives in the apiary proposes the idea that E. faecium EFD is there as a part of the normal beehive microbiota. This finding, in combination with its antibacterial activity against P. larvae, highlights this novel isolate as a potential natural preserving agent against AFB. Furthermore, the WGS-based approach reported here proved to be very cost- and time- efficient, for screening the applicability of new pro- and prebiotic Enterococcus strains as beehive protection agents.
Keywords: Bacteriocins; Enterococcus faecium; Illumina HiSeq; Whole-genome sequencing.