Purification and characterisation of bacteriocins produced by Enterococcus faecium from Tunisian rigouta cheese

Screening for bacteriocin production by strains of lactic acid bacteria from a Tunisian dairy product resulted in the detection of Enterococcus faecium bacteriocin producing strain. The anti-microbial compounds produced by this novel strain were heat stable and inactivated by trypsin, proteinase K and pronase E. Bacteriocins produced inhibited not only the closely related LAB, but also Listeria monocytogenes and Staphylococcus aureus. RP-HPLC purification of the anti-microbial compounds shows two individually active fractions eluted at 25.5 and 38.5 min, respectively. Mass spectrometry analysis showed that E. faecium MMT21 produce two bacteriocins enterocin A (4828.67 Da) and enterocin B (5463.8 Da). This result was confirmed by amplification by PCR of enterocins A and B genes. The novel bacteriocin producing strain E. faecium MMT21 was not haemolytic, sensitive to vancomycin and other clinically relevant antibiotics and was an antilisterial strain. Therefore, it may be useful to improve the safety of fermented food products.