Bacteriocin-Producing Enterococcus faecium LCW 44: A High Potential Probiotic Candidate from Raw Camel Milk

Abstract

Bacterial isolates from raw camel milk were screened for antibacterial activity using the agar diffusion assay. Ten isolates selected for their inhibition of Gram-positive bacteria were identified by 16S sequencing as <i>Enterococcus faecium</i> or <i>durans</i>. An isolate named <i>E. faecium</i> LCW 44 exhibited the broadest antibacterial spectrum with an inhibitory activity against several Gram-positive strains belonging to the genera <i>Clostridium</i>, <i>Listeria</i>, <i>Staphylococcus</i>, and <i>Lactobacillus. E. faecium</i> LCW 44 was shown to produce N-formylated enterocins L50A and L50B, as revealed by mass spectrometry and PCR analyses. This isolate did not harbor any of the virulence factors tested and was shown to be sensitive to all tested antibiotics. It showed high resistance to gastric and intestinal conditions (78 ± 4% survival). Its adhesion index was evaluated at 176 ± 86 and 24 ± 86 on Caco-2 cells and HT-29 cells, respectively, and it significantly reduced adhesion of <i>Listeria monocytogenes</i> by 65 and 49%, respectively. In Macfarlane broth (simulating the nutrient content of the colon), counts of <i>L. monocytogenes</i> were reduced by 2 log₁₀ cycles after 24 h in co-culture with <i>E. faecium</i> LCW 44, compared to the increase of 4 log₁₀ cycles when cultured alone. Comparison with a bacteriocin-non-producing mutant of <i>E. faecium</i> LCW 44 strongly suggests that inhibition of <i>L. monocytogenes</i> was due to bacteriocin production. Altogether, <i>E. faecium</i> LCW 44 thus has potential for use as a probiotic for humans and veterinary medicine.