Isolation and characterization of a novel lytic phage WAH1 against multidrug-resistant Bacillus cereus and its application in food matrices.

Foodborne diseases caused by Bacillus cereus (B. cereus) pose a serious threat to public health. Phages offer a promising biocontrol strategy, but phage resources targeting B. cereus remain limited. In this study, a novel lytic phage, WAH1, was isolated from sewage using a multidrug-resistant B. cereus strain as the host. Morphological analysis revealed that WAH1 possesses an icosahedral head and a long, contractile tail. WAH1 exhibits a broad host range, lysing 33 out of 51 (64.7%) B. cereus strains covering 17 sequence types (STs), as determined by multilocus sequence typing (MLST). The phage maintained high stability under various environmental stresses, retaining activity at 4-45 °C, pH 5-11, and 2-10% NaCl concentrations. One-step growth curve showed a latent period of 40 min and a burst size of 114 PFU/cell. Genomic analysis classified WAH1 within the genus Caeruleovirus, family Herelleviridae; its genome is a linear double-stranded DNA of 156,276 bp, containing 224 open reading frames and 20 tRNAs, and carries no antibiotic resistance genes, virulence factors, or lysogeny-associated genes. WAH1 not only exhibited potent, dose-dependent lytic activity against the host strain (with no bacterial regrowth within 36 h) but also significantly prevented biofilm formation. Importantly, WAH1 effectively reduced or completely eliminated B. cereus in food matrices (milk, rice, and meat) in a dose- and time-dependent manner at both 25 and 4 °C, without bacterial regrowth. These results indicate that phage WAH1 is a promising biocontrol agent against B. cereus and holds great potential for application in various food products.