A strain of Enterococcus mundtii has probiotic qualities. The strain of E. mundtii (ST4SA) produces an antimicrobial peptide which exhibits antimicrobial activity against a broad range of bacteria. An isolated nucleotide sequence codes for the antimicrobial peptide (peptide ST4SA). A process is also provided for the production of a peptide which comprises cultivating Enterococcus mundtii strain ST4SA in a nutrient medium under micro-aerophilic conditions at a temperature of between 10° C. and 45° C., until a recoverable quantity of the peptide is produced, and recovering the peptide. The isolated peptide 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.