CO-Based micro-respirometry for measuring bacterial load under aerobic and anaerobic conditions.

The bacterial load (BL), or total viable count, of aerobes can be measured using micro-respirometry, %O-μR, in which the consumption of dissolved O is monitored with respect to incubation time, . In %O-μR the 'bioreactor' often comprises a canonical plastic tube with a small %O sensor; it is simple, fast and accurate and used in automated, commercial instruments for measuring BL. Here we show that it is also possible to measure BL using a new form of micro-respirometry, %CO-μR, in which the production of CO in the growth medium is monitored. In %CO-μR, the 'bioreactor' is the same as that used in %O-μR, but with a small 3D printed, colour-based %CO indicator set in its base and its apparent absorbance, ', is measured at any , as it is related to the %CO dissolved in the inoculated growth medium. Under conditions, different inoculations of the facultative anaerobe, , of different concentrations (10-10 colony forming units (CFU) per mL) are used to generate a series of ' . profiles, and a straight-line calibration curve. Statistical comparative analysis of the results generated in the above %CO-μR study, to those generated for the same system but using a commercial %O-μR system, is used to demonstrate method equivalence. A study of the same system, under anaerobic conditions, using %CO-μR, shows that %CO-μR is suitable for measuring the BL of anaerobes. The potential of %CO-μR for measuring the bacterial load of CO-generating aerobes and anaerobes is discussed briefly.