[Estimating the biological effect of detrimental substances on E. coli with flow microcalorimetry. III. Studies using m-cresol in glucose phosphate buffer].

Investigations are carried out to characterize the influence of the phenolic compound m-cresol on the heat production of glucose-respiring E. coli cells suspended in glucose phosphate buffer in a flow microcalorimeter according to the method of Perry et al. (5) The results are usually obtained within one hour. When testing m-cresol by this method thermic irritations occurred. A modified test procedure which largely avoids these troubles is described. The height (Q = heat flow) of the power-time-curves is evaluated 30 min and 60 min after the addition of the test substance. These values are compared to the values obtained from control-curves without any test substance. The 60 min-values seem less variable than the 30 min-values. The minimum effective m-cresol concentrations come to 7.50 mmol/l after 30 min and to 9.37 mmol/l after 60 min. The coefficients of variation are distinctly lower than +/- 10% at concentrations of less than 11.25 mmol/l. The coefficients of variation from 3 to 5 tests can extend +/- 20% both for the 30 min-values and the 60 min-values at higher concentrations (e.g. 15 mmol/l). Under the influence of increasing m-cresol concentrations the germ content in the solution and the heat flow decrease in a similar way. The results indicate that the used flow microcalorimetric technique is suitable to check the effect of a test substance on a test culture within only one hour's time. Possibly, the method can be helpful for pretesting disinfectants. The gathering of further experience with this system seems advisable.