This work assesses, with epifluorescence microscopy and an image analysis method, glucose and amino acid metabolisms as carbon sources during pristinamycin batch production process in correlation with intracellular pH-variations. At the start of the culture, results suggested preferential consumption of glutamate as carbon source over glucose and arginine. Besides, sequential use of glutamate and arginine as nitrogen sources has been observed, glutamate being assimilated before arginine. Once the glutamate is exhausted, glucose and arginine begin to become metabolised. Shortly before pristinamycin excretion, a massive lactate and succinate excretion occurs. Excretion of pristinamycins and organic acids and glucose and amino-acid consumption were shown to be correlated to measured intracellular pH-fluctuations, so that many cytoplasmic pH-variations can be explained by this study. (C) 2003 Elsevier Inc. All rights reserved.