When and why do decontamination processes underperform against multispecies biofilms in food-processing environments?

Multispecies biofilms are recurrent targets of hygiene failures in food-processing environments, yet their response to decontamination is still often inferred from planktonic or single-species models. This review examines when and why multispecies organization modifies stress tolerance, treatment efficacy, and post-treatment recovery in food-relevant biofilms. Rather than treating multispecies biofilms as universally resistant in the strict dose-response sense, we distinguish the effects of sessile growth from those of community organization by comparing planktonic single-species cells, surface-attached cells, single-species biofilms, and multispecies biofilms across chemical, thermal, non-thermal, oxidative, and environmental stresses. The available evidence indicates that reduced decontamination performance is most consistently observed for chemical sanitation, where shared matrix production, spatial shielding, organic residues, and treatment neutralization can lower the effective dose reaching embedded cells. For thermal and non-thermal treatments, the evidence is more context-dependent and often reflects the way temperature, moisture, surface properties, and prior environmental history shape the biofilm before treatment. Multispecies tolerance emerges from interacting mechanisms, including extracellular matrix protection, diffusion limitation, physiological gradients, phenotypic heterogeneity, viable but non-culturable states, interspecies cross-protection, and community reorganization after disturbance. However, protection is not uniform across taxa: the same community may protect one species while suppressing another, and immediate log reduction may poorly predict long-term control. We therefore propose that food decontamination strategies should move beyond simplified efficacy tests and incorporate realistic multispecies models, matrix-disrupting steps, viable-survivor monitoring, and multi-hurdle designs that account for surface, residue, community composition, and sanitation history.