The invention relates to a strain of Enterococcus mundtii having probiotic qualities. The strain of E. mundtii (ST4SA) produces an antimicrobial peptide which exhibits antimicrobial activity against a broad range of bacteria. The invention also provides an isolated nucleotide sequence which codes for the antimicrobial peptide (peptide ST4SA). Another aspect of the invention relates to a process for the production of a peptide of the invention which comprises cultivating Enterococcus mundtii strain ST4SA in a nutrient medium under micro-aerophilic conditions at a temperature of between 100 C. and 45° C., until a recoverable quantity of said peptide is produced, and recovering said peptide. The isolated peptide of the invention may be used as an antimicrobial agent in a liquid formulation or a gel formulation as a topical treatment and may also be used as an antimicrobial agent following encapsulation in a polymer.