Antibacterial and antioxidant activities of acid and bile resistant strains of lactobacillus fermentum isolated from Miang

Miang is a kind of traditional fermented tea leaves, widely consumed in northern Thailand as a snack. It contains several kinds of Lactobacilli spp. The aim of this study was to isolate strains of Lactobacillus fermentum from miang and to investigate their antibacterial and antioxidant activities. The agar spot and well assays were used for determination of antibacterial power. The antibacterial mechanism was investigated by cell morphologic change under scanning electron microscope (SEM). Antioxidant activity was studied by means of free radical scavenging and ferric reducing power assays. The acid and bile screening tests indicated that L. fermentum FTL2311 and L. fermentum FTL10BR presented antibacterial activity against several pathogenic bacteria: Listeria monocytogenes DMST 17303, Salmonella Typhi DMST 5784, Shigella sonnei DMST 561 (ATCC 11060)and Staphylococcus aureus subsp. aureus DMST 6512 (ATCC 6538Ptm). The results from SEM suggested that the antibacterial action was due to the destruction of cell membrane which consequently caused the pathogenic cell shrinking or cracking. The antioxidant study suggested that both L. fermentum FTL2311 and L. fermentum FTL10BR strains could liberate certain substances that possessed antioxidant activity expressed as trolox equivalent antioxidant capacity (TEAC) and equivalent concentration (EC) values for free radical scavenging and reducing mechanisms, respectively. The supernatant of L. fermentum FTL2311 broth revealed TEAC and EC values of 22.54±0.12 and 20.63±0.17 µM.mg-1 respectively, whereas that of L. fermentum FTL10BR yielded TEAC and EC values of 24.09±0.12 and 21.26±0.17 µM.mg-1 respectively. These two strains isolated from miang present high potential as promising health-promoting probiotics.

An alternative method for evaluation of resistance to low pH and bile salts in probiotic characterization of Lactobacillus reuteri strains: a technical note

A considerable amount of attention has been focused on the use of lactobacilli as probiotics. The use of microorganisms as probiotics must meet certain criteria, among these; the resistance to low pH and bile salts is of great importance. Different procedures have been designed to evaluate tolerance to gastrointestinal transit. Since resistance to low pH and bile salts is critical in the evaluation of probiotic strains, the aim of this study was to compare resistance to bile salts for 20 strains of porcine Lactobacillus reuteri that had been isolated from healthy pigs, using two different procedures based on exposure to low pH. Statistical analysis revealed no difference in resistance of the strains to bile salts whether pH was low or not. The use of low pH prior to exposure to bile salts therefore more closely represents physiological conditions that should be used for the evaluation of potential porcine probiotic lactobacilli. Further studies using digestive enzymes are required to evaluate resistance to gastrointestinal transit, since it is an important factor in the evaluation of strains with potential probiotic activity.

Existe un interés creciente en el uso de lactobacilos como probióticos. El uso de microorganismos como probióticos, requiere que éstos cubran ciertos requisitos, dentro de los cuales la resistencia a pH ácido y a sales biliares, se consideran de suma importancia. Actualmente existen distintos procedimientos que permiten evaluar la tolerancia al tránsito gastrointestinal. Debido a que la resistencia a pH ácido y a sales biliares es una condición crítica dentro de la evaluación de cepas probióticas, la finalidad del presente trabajo consistió en comparar la resistencia a sales biliares de 20 cepas de Lactobacillus reuteri aisladas de cerdos sanos, mediante dos procedimientos diferentes basados en la exposición a pH ácido. El análisis estadístico no mostró diferencias en la resistencia de las cepas a sales biliares cuando se realizó una exposición previa a pH ácido. Así, la exposición a pH ácido previo a la incubación con sales biliares, asemeja más a las condiciones fisiológicas que el microorganismo encontrará de manera natural y es una buena alternativa en la evaluación probiótica de lactobacilos de origen porcino. Se requieren estudios que incluyan enzimas digestivas, con el fin de evaluar la resistencia al tránsito gastrointestinal, dado que es uno de los factores más importantes en la evaluación de cepas con potencial actividad probiótica.