The present invention provides an agent, or a composition containing an agent, for use in treating or preventing a bacterial infection in a subject, wherein said agent comprises: (i) an oligopeptidic compound comprising a PCNA interacting motif and a domain that facilitates the cellular uptake of said compound, wherein the PCNA interacting motif is X1X2X3X4X5 (SEQ ID NO: 1) and wherein: X1 is a basic amino acid; X2 is an aromatic amino acid; X3 is an uncharged amino acid other than an aromatic amino acid, Glycine (G) and Proline (P); X4 is any amino acid other than Proline (P), an acidic amino acid or an aromatic amino acid; and X5 is a basic amino acid or Proline (P); or (ii) a nucleic acid molecule comprising a sequence encoding the oligopeptidic compound of (i). In certain aspects the agent and compositions of the invention may be used as single agents. In other aspects of the invention agents and compositions of the invention may be used in conjunction with one or more additional active agents, such as antibiotics.