When E. coli ML 30 is grown in batch culture on a mineral salt medium containing a mixed carbon source of glucose and pyruvate, there is no sequential utilization of the carbon sources. The consumption of glucose and pyruvate takes place simultaneously with reciprocal influence (inhibition) on rates of substrate uptake. The specific growth rate is greater than mupmax for pyruvate but smaller than musmax for glucose. In the paper three cases of kinetics of growth and of substrate consumption at several combinations of initial substrate concentrations are considered. A mathematical model is proposed and investigated. The model allows to describe the growth on glucose or on pyruvate not only as singular carbon sources, but also as a mixed carbon source with reciprocal inhibition on rates of substrate uptake. By data fitting parameters of growth and substrate consumption were found.