[Aerobic conditions and the dynamics of the methyl red reaction in Klebsielleae]

The development of the methyl red reaction (MR) in Klebsielleae, analyzed during a 4-day thermostatting, showed important pH-variations. Two steps are distinguished during the reaction dynamics: the former of acidification, common to all Enterobacteriaceae and the latter of alkaline reversion, specific to Enterobacter, Klebsiella, Serratia and other MR germs. The processes determining the alkaline reversion are conditioned by the presence of large amounts of air/oxygen (aerobic processes). In this situation, the lack of oxygen and maintenance of a relative degree of anaerobiosis block realkalinization (media covered with paraffin oil) whereas the large aeration stimulates it (optimum ratio between the large contact surface and a small volume of medium). Alkaline reversion cannot be explained by the more or less intense process of glucose fermentation but by degradations of nitrogenized substances with formation of amines, ammonia, and other basic compounds. That is why the analysis of the reaction mechanism of methyl red has to consider the characteristics of the catabolism of the nitrogenized substances and the intense realkalinization capacity of the culture medium proper to Klebsielleae but poorly expressed and non efficient in Enterobacteriaceae.