Growth advantage of Streptococcus thermophilus over Lactobacillus bulgaricus in vitro and in the gastrointestinal tract of gnotobiotic rats
2012
Benyahia, Lazhar | Mayeur, Camille | Rul, Francoise, F. | Thomas, Muriel | MICrobiologie de l'ALImentation au Service de la Santé (MICALIS) ; Institut National de la Recherche Agronomique (INRA)-AgroParisTech | Syndifrais-CNIEL
The yoghurt bacteria, Streptococcus thermophilus and Lactobacillus delbrueckii ssp. bulgaricus, are alleged to have beneficial effects on human health. The objective of this study was to characterise growth, biochemical activity and competitive behaviour of these two bacteria in vitro and in vivo. S. thermophilus LMD-9 and L. bulgaricus ATCC 11842 growth and lactate production were monitored in different media and in the gastrointestinal tract (GIT) of germ-free rats. In vitro, particularly in milk, S. thermophilus had a selective growth advantage over L. bulgaricus. The GIT of germ-free rats not supplemented with lactose was colonised by S. thermophilus but not by L. bulgaricus. Both bacteria were able to colonise the GIT of germ-free rats supplemented with 45 g/l lactose in their drinking water. However, if germ-free rats were inoculated with a mixture of the two bacteria and were supplemented with lactose, S. thermophilus rapidly and extensively colonised the GIT (10(10) cfu/g faeces) at the expense of L. bulgaricus, which remained in most cases at levels < 10(2) cfu/g faeces. S. thermophilus specifically produced L-lactate, while L. bulgaricus produced only D-lactate, both in vitro and in vivo. S. thermophilus showed competitive and growth advantage over L. bulgaricus in vitro as well as in vivo in the GIT of germ-free rats and, accordingly, L-lactate was the main lactate isomer produced.
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