Fast respirometry-based system for on-site quantification of total viable counts on surfaces

We introduce a new biosensor platform based on oxygen respirometry, for rapid and simple quantification of total aerobic viable counts of bacteria (TVC) on surfaces. This system adopts a convenient swab sachet format, with an integrated phosphorescent O₂ sensor and a handheld reader for seamless signal readout. In our approach, surface swab samples are collected according to the standard method (ISO18593:2018)¹ and placed inside the disposable sensor sachets². The sachets are subsequently zip- sealed and incubated at 30 °C measuring sensor signals hourly, ensuring a contactless and non- invasive procedure. Measurements unveil time profiles of dissolved O₂ in each sachet, enabling the determination of the Time-to-reach-Threshold for the sensor signal (TT)³. Subsequently, TVC values (CFU/cm²) are calculated using a calibration equation. The method spans the range of 0.5–7 Log(CFU/cm²) and provides results in 2-12 hours. Validation of the test was conducted, initially using swab samples from surfaces artificially contaminated with E. coli and whole meat microbiota, and finally with real food and environmental swabs. The results exhibited no significant differences with the reference ISO method, which typically requires 48–72 hours. Notably, our swab testing platform prioritizes safety, as the sachets are promptly and permanently sealed after sampling, ensuring operators are not exposed to potential biohazards. Additionally, the system eliminates the need for refrigerated sample transport. Once swabs are collected, they can be placed in a portable incubator and transported to the laboratory or facility for data analysis. This feature adds convenience to the whole testing process, making it more efficient and secure.