Characterisation of a SapYZU11@ZnFe 2 O 4 biosensor reveals its mechanism for the rapid and sensitive colourimetric detection of viable Staphylococcus aureus in food matrices.

Although bacteriophage-based biosensors hold promise for detecting Staphylococcus aureus in food products in a timely, simple, and sensitive manner, the associated targeting mechanism of the biosensors remains unclear. Herein, a colourimetric biosensor SapYZU11@ZnFe ₂ O ₄ , based on a broad-spectrum S. aureus lytic phage SapYZU11 and a ZnFe ₂ O ₄ nanozyme, was constructed, and its capacity to detect viable S. aureus in food was evaluated. Characterisation of SapYZU11@ZnFe ₂ O ₄ revealed its effective immobilisation, outstanding biological activity, and peroxidase-like capability. The peroxidase activity of SapYZU11@ZnFe ₂ O ₄ significantly decreased after the addition of S. aureus, potentially due to blockage of the nanozyme active sites. Moreover, SapYZU11@ZnFe ₂ O ₄ can detect S. aureus from various sources and S. aureus isolates that phage SapYZU11 could not lyse. This may be facilitated by the adsorption of the special receptor-binding proteins on the phage tail fibre and wall teichoic acid receptors of S. aureus. Besides, SapYZU11@ZnFe ₂ O ₄ exhibited remarkable sensitivity and specificity when employing colourimetric techniques to rapidly determine viable S. aureus counts in food samples, with a detection limit of 0.87 × 10 ²  CFU/mL. Thus, SapYZU11@ZnFe ₂ O ₄ has broad application prospects for the detection of viable S. aureus cells on food substrates.
Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
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