Inactivation action of ultrasound-assisted cinnamaldehyde on planktonic and biofilm methicillin-resistant Staphylococcus aureus and its application in beef system

There has been a growing concern for methicillin-resistant Staphylococcus aureus (MRSA) contamination in the food industry. In the present study, the highest inactivation effect (5.80 log CFU/mL) was observed in simultaneous treatment compared with sequential treatment of ultrasound (US)-assisted cinnamaldehyde (CA). The absence of sublethal bacteria indicated US-assisted CA did not induce the tolerance or adaptation to MRSA cells. The results of SEM analysis indicated that the application of US-assisted CA resulted in severe damage to the cell membrane, as demonstrated by the highest fluorescence intensity of propidium iodide dye, intracellular substance leakage, and molecular docking analysis, as well as ATPase activity. Furthermore, US-assisted CA significantly disrupted energy metabolism, as evidenced by a reduction in ATP concentration, succinate dehydrogenase, and malate dehydrogenase activities. The exacerbation of ROS-induced damage to MRSA cells was observed due to the reduction in catalase and peroxidase activities. Additionally, a significant decrease (p < 0.05) in extracellular carbohydrates and proteins within the MRSA biofilm was noted on both glass and stainless-steel surfaces exposed to US-assisted CA. Ultimately, US-assisted CA treatment resulted in a maximum reduction (p < 0.05) of MRSA cells in beef meat, while maintaining color, pH, and sensory properties during an 8-day storage period at 4 °C. These findings suggested that simultaneous US-assisted CA treatment may serve as an alternative method for ensuring microbiological safety.