Otimização das condições de cultivo laboratorial de bactérias láticas e probióticas e avaliação do comportamento de <i>Lactobacillus casei</i> no trato gastrintestinal através de modelos simulados <i>in vitro</i>

Abstract

The beneficiai effects of probiotic bacteria to the human health depend on their quantity and biological activity in the human gut. This study aimed to establish the best laboratorial conditions for the differential cultivation and enumeration of five bacterial cultures, including three probiotic (Bifidobacterium animalis Bb12, Lactobacillus acidophilus La05 and Lactobacillus casei Lc01) and two nonprobiotic (Lactobacillus delbrueckii subsp. bulgaricus and Streptococcus thermophilus) strains. In addition, this study also aimed to evaluate the capability of two probiotic strains (Lactobacillus casei Shirota and Lc01) to survive the transit through the human gastrointestinal tract, using in vitro simulated models. Twenty one different culture media were tested. They were inoculated using pour-plating and spread-plating techniques. Plates were incubated at 37°C and 42°C, under aerobiosis and anaerobiosis. Resistance to the gastrointestinal tract was tested using simulated models, constituted by 0.5% saline containing pepsin (3g/L) at pH 1.5, 2.0, 2.5 and 3.0 (gastric juice) and by 0.5% saline containing pancreatin (1g/L) and bile (10g/L) at pH 8.0 (enteric juice). The cultures were exposed to gastric juice (up to 120min) and then to enteric juice (up to 240min). Results indicated that supplementation of MRS agar with certain compounds and use of appropriate combinations of plating procedures and incubation conditions can turn MRS agar a selective and differential medium for the tested species. The combination MRS agar at pH 5,4, pour-plating and incubation at 37°C under aerobiosis was selected for evaluation of resistance of the L. casei (Shirota e Lc01) to the gastrointestinal tract. Results indicated that xvii both eultures beeame non-eulturable after 30min exposure to the gastrie juiee at pH 1.5 and 2.0. After 2h at pH 2.5, a 4 log reduetion was observed. At pH 3.0, no ehange in the number of viable eells was detected. The subsequent transfer to the enterie juiee eaused a partiaI reversion in injury indueed by the acid pH. In addition, it was observed that milk ean proteet the probiotie baeteria from the stress eaused by the transit through the gastrointestinal tract.