Prevalence and genomic insights into enterotoxin-producing Bacillus cereus group in the dairy production chain through whole-genome analysis

Bacillus cereus group is a common and ubiquitous foodborne pathogen with increasing prevalence at several stages of the farming chain. In this study, the prevalence and genomic characteristics of B. cereus group isolates from the dairy production chain in Shandong, China, were investigated. A total of 480 samples from 3 dairy farms located in Shandong were collected. The overall prevalence of B. cereus group isolates was 15.6% (75/480). All isolates were resistant to penicillin, amoxicillin/clavulanic acid, and ampicillin, with 18.7% exhibiting multidrug resistance. Whole-genome sequencing (WGS) of all isolates revealed 2 antibiotic resistance genes: blaZ and fosB1, present in 6.7% and 44.0% of isolates, respectively. Among major virulence genes, nheABC was ubiquitous (100%), whereas cytK and hblCDA were detected in 73.3% and 52.0% of isolates, respectively. Multilocus sequence typing (MLST) assigned 52 of 75 isolates to 32 known sequence types (ST), with ST177 being the most common (9.3%). The remaining 23 isolates could not be typed. FastANI analysis confirmed that all 75 isolates belonged to the B. cereus group (average nucleotide identity [ANI] >90%), and MLST failure occurred even among some isolates with ANI >95%, indicating limitations in the current MLST database. This study provides WGS-based genomic insights into the enterotoxigenic potential and genetic diversity of B. cereus group isolates from the dairy production chain. Our findings demonstrate a high prevalence of broadly resistant and genetically diverse B. cereus group harboring multiple toxin genes. This underscores a potential One Health concern, linking animal, environmental, and public health through the risk of foodborne illness.