Probiotic potential of Enterococcus strains with multiple enterocin-encoding genes

Abstract

In this work, we sought to identify and characterize three strains of Enterococcus isolated from camel milk and fermented wheat, based on the capacity to produce bacteriocins and the probiotic potential. Polymerase chain reaction analyses were used to identify bacterial isolates and structural genes of bacteriocins, and also to detect potential enterococcal virulence genes (cylA, esp, gelE, efaAfs, hyl, ace, asa1, vanA, and vanB). The antimicrobial activity of the strains was investigated in solid media by the agar spot method against several pathogenic bacteria. The probiotic potential of the strains was also analysed using low pH (pH 3.0), bile salt resistance, DNAase, and antibiotic susceptibility assays. The strains were identified using rRNA16S sequencing gene, showing their belonging to E. faecium species. Based on PCR results, E. faecium CM9 and CM18 strains included in the genome the structural gene of enterocin A, enterocin B, and enterocin P, while E. faecium H3 possessed enterocin MR10A/B structural gene. The sequence analysis revealed that the H3 strain included in the genome the structural gene of enterocin L50A/B. All the pathogenic bacteria (Staphylococcus aureus, Salmonella enterica, Listeria monocytogenes, E. coli, and Pseudomonas aeruginosa) were inhibited by the three strains E. faecium CM9, CM18, and H3. In the well diffusion test, the supernatants of the three strains exhibited inhibitory activity against Listeria monocytogenes CECT 4032. The strains showed high tolerance to low pH and bile salts, did not possess DNase, were susceptible to the majority of antibiotics assayed, and did not possess any of the virulence genes analyzed in this study. A promising candidate strains were identified as potential probiotics with anti-bacterial action against pathogenic bacteria.