Western blot analysis was carried out on crude extracts from 72-h cultures of the W. anomalus strains 1F1 and ATCC 96603 (KT-producing, positive control strain). As a negative control, a crude extract from W. anomalus UM3 (KT-nonproducing strain) culture and 50-fold concentrated YPD medium were used. Bands were detected with mAbKT4, a monoclonal antibody directed against a KT produced by the reference ATCC 96603 strain (Wa96603-KT) and shown to cross-react with KTs produced by other W. anomalus strains and other killer yeasts . The results showed that mAbKT4 reacts with high-molecular mass proteins in samples obtained from W. anomalus 1F1 and ATCC 96603, but not from controls (Figure 2). A single band of approximately 220 kDa was revealed in extracts from the reference strain, while a single band with a lower molecular mass (approximately 160–170 kDa) was detected in the extract from 1F1 strain, indicating the secretion of KTs with a common epitope, although with some structural differences.