Lytic phage-based magnetoelastic biosensors for on-site detection of methicillin-resistant Staphylococcus aureus on spinach leaves

A lytic phage-based magnetoelastic (ME) biosensor method was firstly employed for on-site detection of methicillin-resistant Staphylococcus aureus (MRSA) on spinach leaves. Due to the virulent activity of this lytic phage, the effect of time and temperature on the extent of MRSA lysis was examined by incubating a mixture of the MRSA and lytic phage at various times (0, 15, 30, 45, 60, 75, and 90 min) and temperatures (0, 4, 15, 22, 37, and 45°C). After optimization of incubation time and temperature, spinach leaves were spiked with serial concentration of MRSA and the attachment of MRSA was confirmed using SEM. The phage-immobilized sensor and control (devoid of the lytic phage) sensor were placed on the surface of the leaves and the resonant frequency shifts of both sensors were compared. The optimal incubation time and temperature for contact of the phage-immobilized ME biosensor with the MRSA were determined to be ≥ 30 min and ≥ 22°C. The attachment of the lytic phage on the sensor was observed and the density of lytic phage on the sensor was determined to be 26 ± 3 particles/μm². The resonant frequency shifts of the phage-immobilized sensor linearly increased with the increase in the MRSA concentration and had a correlation coefficient and slope of 0.819 and 840.9 Hz/log CFU, respectively. Detection limit was determined to be 1.76 log CFU/25 mm² surface of spinach.