One hypothesis is that the effect of the volume mean power dissipation could be indirect, through a modification of mass transfers including oxygen transfer. Therefore, kLa was calculated according to a correlation previously published [24] and [25] for all batch cultures and the presence or absence of antibiotics production was plotted against the calculated values of kLa ( Fig. 6). As for the volume mean power dissipation, production occurred only for the values of kLa, superior to 100 h−1, whatever the type of flask used. On the contrary, no production was observed for values of kLa inferior to 80 h−1. In-between those two extreme zones, there was no correlation between kLa and the presence of antibiotics (overlapping zone).