Fig 1: Determined epitopes of the MAbs against DHA-177−93 and the results of cross-reactivity testing. (a) Representation of synthetic peptides (P0–P1) used for fine mapping of MAb epitopes. P0 peptide corresponds to DHA-177−93 aa sequence. (b) Schematic representation of MAb recognition sites within DHA-177−93. Based on the determined recognition sites, two groups of MAbs (Group 1 and Group 2) are identified. The epitope recognised by Group 1 MAbs is marked with an upper line. The epitope of Group 2 MAbs is underlined. (c) Visualisation of the determined MAb epitopes in the DHA-1 protein. DHA-177−93, corresponding to the 77–93 aa region in the DHA-1 protein, is coloured violet, the epitope of Group 1 MAbs (79–89 aa region) is coloured yellow, and the epitope of Group 2 MAbs (85–93 aa region) is marked in orange. The image of the DHA-1 protein (23–379 aa) without a signal sequence (AlphaFold Protein Structure Database, No. AF-G5DDZ0-F1-v4) is shown. (d) Alignment of aa sequences of DHA-177−93 and homologous regions of β-lactamases used for MAb characterisation. The positions of mismatched aa are highlighted in yellow. (e) Alignment of the 79–89 aa region of DHA-1, recognised by Group 1 MAbs, with homologous regions of ADC, PDC, ACT, CMY (highlighted in purple) and other families of AmpC β-lactamases sharing the same region. The differences in the aa sequences are coloured yellow. (f) Synthetic peptides (AmpC-P1–AmpC-P9) used for MAb cross-reactivity testing and their alignment with the 79–89 aa recognition site of Group 1 MAbs. The mismatched aa are coloured yellow. Each peptide corresponds to a group of AmpC β-lactamases sharing the same homologous region. (g) The reactivity of Group 1 MAbs with synthetic peptides (AmpC-P1–AmpC-P9) tested by ELISA. The results are presented as apparent affinity values (nM).