Lactose and Galactose Fermentation in Staphylococci.

Abstract

Fermentation of mannitol, lactose, and galactose in 5 isolates of oral staphylococci was studied calorimetrically with bromothymol blue (BTB) as a pH indicator. As expected, mannitol fermentation was demonstrated in two coagulase-positive (Staphylococcus aureus) strains, but not in three coagulase-negative (S. epidermidis) ones. The S. aureus strains fermented both lactose and gelactose, which is consistent with the finding that these strains possess lactoe (gelactose)-specific phosphoenolpyruvate : sugar phosphotransferase system (Lac PTS ; Fujisawa, A. this Bulletin 9 : 15-18,1987). Two S. epidermidis strains fermented lactose with rates comparable to those found in S. aureus strains. One of them also fermented galactose efficiently, whereas little fermentation of this sugar was observed in the other strain. The third S. epidermidis strain fermented galactose, but not lactose at all. These findings, as well as those reported previously that no or little Lac PTS activity was demonstrated in these three strains, strongly suggest that, in S. epidermidis, lactose and galactose are metabolized via a different pathway or pathways from that operating in S. aureus.