Facile biosensor-based system for on-site quantification of total viable counts in food and environmental swabs

We describe a new biosensor platform for rapid and simple quantification of total aerobic viable counts of bacteria (TVC) in food and environmental swabs by oxygen respirometry. The system uses disposable swab vials with phosphorescent oxygen sensors integrated in the bottom part, a small block heater/incubator and a handheld sensor reader. In the testing, groups of 1-20 swabs samples were prepared using the standard method (ISO, 18593:2018) in sensor vials, which were then incubated at 30 °C and measured hourly in a contactless, non-invasive manner. The measurements reveal time profiles of dissolved O in each sample vial, from which Threshold Time of sensor signal was determined and then TVC values (CFU/cm) were calculated using the calibration equation. The method covers the range of 0.65-7.87 Log (CFU/cm) and produces results in 1-8 hrs. The test was validated with swab samples from surfaces contaminated with E. coli, with whole meat microbiota, and with real environmental swabs. The results showed no statistically significant difference with the reference method which takes 48-72 h. The swab testing platform is fast and accurate, simple (sample-and-measure), portable, low cost (<$5k), requires no serial dilutions and is suitable for on-site deployment and use.