Urban-Adjacent Soils as a Global Reservoir of Toxigenic and Antimicrobial-Resistant Bacillus cereus Sensu Lato.

Bacillus cereus sensu lato (B. cereus s.l.) is ubiquitous in soil, but the extent to which urban-adjacent soils act as reservoirs of antimicrobial-resistant and potentially toxigenic lineages remains poorly understood globally. We analysed 243 B. cereus s.l. isolates representing unique sequence types from ten urban locations worldwide. Population structure was assessed by multilocus sequence typing and phylogenetic analyses, antimicrobial susceptibility by disk diffusion and MIC determination, and the presence and expression of nheA, hblA, and cytK by PCR and qPCR. Isolates from the same locations clustered on the phylogenetic tree more frequently than expected by chance, although isolates from different regions remained widely intermingled. Selected lineages also showed significant latitudinal distributions. Antimicrobial susceptibility varied markedly among locations, with frequent ampicillin resistance and geographic differences in cumulative elevated MIC burden that were not consistently associated with local phylogenetic clustering. These patterns may reflect region-specific anthropogenic selective pressures. The nheA gene was detected in all isolates, whereas hblA and cytK occurred in approximately half, and neither gene carriage nor relative expression was associated with elevated MIC burden. Urban-adjacent soils therefore harbour phylogenetically diverse B. cereus s.l. populations with widespread enterotoxin-associated genetic potential and geographically heterogeneous antimicrobial resistance.