A nucleic acid molecule comprising a polynucleotide selected from the group consisting of: (a) a polynucleotide encoding a polypeptide having the amino acid sequence of SEQ ID NO: 2; (b) a polynucleotide encoding a fragment, analog or functional derivative of a polypeptide encoded by the polynucleotide of (a), wherein said fragment, analog or functional derivative has binding specificity for bacteriophage receptors on Listeria cells; (c) a polynucleotide which is at least 75% identical to the polynucleotide of (a), and which encodes a polypeptide having binding specificity for bacteriophage receptors on Listeria cells; (d) a polynucleotide encoding a polypeptide having an amino acid sequence that is at least 75% identical to the amino acid sequence of SEQ ID NO: 2 and having binding specificity for bacteriophage receptors on Listeria cells; (e) a polynucleotide which hybridizes under stringent conditions to the polynucleotide of any one of (a) to (d); (f) a polynucleotide comprising the nucleotide sequence of SEQ ID NO: 1; (g) a polynucleotide which is at least 75% identical to the nucleotide sequence of SEQ ID NO: 1 and which encodes a polypeptide having binding specificity for bacteriophage receptors on Listeria cells; (h) a polynucleotide comprising part of the nucleotide sequence of (f) and which encodes a fragment, analog or functional derivative of the polypeptide having the amino acid sequence of SEQ ID NO: 2, wherein said fragment, analog or functional derivative has binding specificity for bacteriophage receptors on Listeria cells; and (i) a polynucleotide that is the complement of the full length of a polynucleotide of any of (a) to (h). (a) a polynucleotide encoding a polypeptide having the amino acid sequence of SEQ ID NO: 2; (b) a polynucleotide encoding a fragment, analog or functional derivative of a polypeptide encoded by the polynucleotide of (a), wherein said fragment, analog or functional derivative has binding specificity for bacteriophage receptors on Listeria cells; (c) a polynucleotide which is at least 75% identical to the polynucleotide of (a), and which encodes a polypeptide having binding specificity for bacteriophage receptors on Listeria cells; (d) a polynucleotide encoding a polypeptide having an amino acid sequence that is at least 75% identical to the amino acid sequence of SEQ ID NO: 2 and having binding specificity for bacteriophage receptors on Listeria cells; (e) a polynucleotide which hybridizes under stringent conditions to the polynucleotide of any one of (a) to (d); (f) a polynucleotide comprising the nucleotide sequence of SEQ ID NO: 1; (g) a polynucleotide which is at least 75% identical to the nucleotide sequence of SEQ ID NO: 1 and which encodes a polypeptide having binding specificity for bacteriophage receptors on Listeria cells; (h) a polynucleotide comprising part of the nucleotide sequence of (f) and which encodes a fragment, analog or functional derivative of the polypeptide having the amino acid sequence of SEQ ID NO: 2, wherein said fragment, analog or functional derivative has binding specificity for bacteriophage receptors on Listeria cells; and (i) a polynucleotide that is the complement of the full length of a polynucleotide of any of (a) to (h).