Enterococcus faecium P21: a strain occurring naturally in dry-fermented sausages producing the class II bacteriocins enterocin A and enterocin B

Abstract

Enterococcus faecium P21 isolated from a Spanish dry-fermented sausage shows a narrow antimicrobial activity against closely related lactic acid bacteria and strong antimicrobial activity against spoilage and foodborne Gram-positive pathogenic bacteria such as Listeria monocytogenes, Staphylococcus aureus, Clostridium perfringens and Clostridium botulinum. The antimicrobial activity is produced during growth in MRS broth at 32°C; it is heat resistant (20 min at 80–100°C) and abolished by protease treatment, and withstands exposure to pH 2–11, freeze-thawing, lyophilization and long term storage at −20°C. Purification of the antimicrobial activity by ammonium sulphate precipitation, gel filtration, and cation-exchange, hydrophobic interaction and reverse-phase chromatographies showed that the broad antimicrobial spectrum exerted by E. faecium P21 was indeed due to two peptide bacteriocins. Studies on theirN -terminal amino acid sequences and PCR and DNA analyses revealed that these bacteriocins are identical to the class II bacteriocins enterocin A and enterocin B. The genetic organization of the enterocin A (EntA) operon in E. faecium P21 shows that the bacteriocin structural gene (entA), the immunity gene (entiA) and the induction peptide gene (entF) are clustered and colinearly arranged. Strikingly, this organization was structurally different to that reported for the EntA-producer E. faecium CTC492.