Disclosed is an antimicrobial peptide fragment of a tammar wallaby milk protein comprising an amino acid sequence selected from the group consisting of SEQ ID NOs: 1-7, 18, 19, and 30-35 or an antimicrobial derivative or analog thereof comprising an amino acid sequence selected from SEQ ID NOs: 1-7, 18, 19 and 30-35 wherein one or more amino acid residues are D amino acid residues or said sequence is reversed or said sequence is retroinverted, and wherein said peptide fragment, derivative or analog has enhanced activity against one or a plurality of gram-negative bacteria relative to an equivalent amount of LL-37 peptide comprising amino acid residues 104-140 of the 18-10a human cationic antimicrobial protein (hCAP18) as determined by a minimal inhibitory concentration (MIC) assay. Also disclosed is the use of the peptides in the preparation of a medicament for reducing or preventing microbial growth.
