Pressure transducer method for measuring gas production by microorganisms.

A simple method for measuring gas production by microorganisms by using a pressure transducer to sense pressure buildup was developed and tested with members of the coliform group. The test system consisted of a 5.0 lb/in(2) pressure transducer and a pressure equalizer valve attached to the metal cap of a test tube (20 by 150 mm); gas pressure was recorded on a strip-chart recorder. Gas pressure response curves consisted of (i) a lag period with no marked increase in pressure, (ii) a rapid pressure buildup period, and (iii) a leveling-off period. A linear relationship was established between inoculum size and length of the lag period. Cultures shaken at 200 oscillations/min showed a marked increase in rate of gas release over stationary cultures. Cell concentrations at the time of rapid buildup in pressure were 10(8)/ml. Mean maximum pressure recordings, lb/in(2) per 10 ml of broth, were: Enterobacter aerogenes, 3.70; Citrobacter intermedium, 2.70; and Escherichia coli, 2.10. Mean CO(2) concentrations, ppm of headspace gas, for E. coli were: (i) 2,000 at time of inoculation, (ii) 25,000 at time of rapid buildup in pressure, and (iii) 150,000 at maximum pressure. These results indicate the potential application of the pressure transducer method for rapidly detecting coliforms and other gas-producing microorganisms in clinical samples and in sterility testing of foods.