title: Molecular analysis of yogurt containing Lactobacillus delbrueckii subsp. bulgaricus and Streptococcus thermophilus in human intestinal microbiota.
abstract: BACKGROUND
  Yogurt has traditionally been considered a probiotic-carrier food with health-promoting effects. Despite the universal assumption of this assertion, several researchers have evaluated the real capability of the yogurt bacteria Lactobacillus delbrueckii subsp. bulgaricus and Streptococcus thermophilus to survive and proliferate in the human intestine and have found contradictory results.
  
  
  OBJECTIVE
  This double-blind crossover study assessed the qualitative and quantitative effects of fresh and heat-treated yogurt on bacterial intestinal microbiota from healthy subjects.
  
  
  METHODS
  The subjects were divided into experimental (n=63) and control (n=16) groups. The experimental group consumed fresh and heat-treated yogurt for 15 d according to a crossover design with a washout period of 2 wk. Three different fecal samples per individual were recovered: at baseline, after fresh yogurt intake, and after heat-treated yogurt intake. Qualitative changes in microbiota were studied by denaturing gel gradient electrophoresis (DGGE) with universal and lactic acid bacteria (LAB) 16S-rRNA primers. Quantitative changes in LAB, Clostridium coccoides, Clostridium perfringens, and Bacteroides groups were analyzed by real-time polymerase chain reaction.
  
  
  RESULTS
  A particular DGGE stable band pattern was observed in each sample. No significant qualitative differences were detected in any fecal sample. However, a significantly higher density of LAB and C. perfringens and a significant decrease in the density of Bacteroides was observed after consumption of both types of yogurt. Microbiota density was not significantly different between the fresh and heat-treated yogurt groups, except for LAB, which was significantly greater in the fresh yogurt group.
  
  
  CONCLUSIONS
  The main change in human microbiota observed after yogurt consumption was an increase in the density of LAB and C. perfringens to the detriment of Bacteroides. Bacterial changes were not different after the consumption of fresh and heat-treated yogurt.
authors.affiliation: Servicio de Microbiología, Hospital Universitario Ramón y Cajal and CIBER en Epidemiología y Salud Pública, Madrid, Spain.
authors.forename: Raimundo
authors.initials: R
authors.lastname: García-Albiach
authors.forename: María José
authors.initials: MJ
authors.lastname: Pozuelo de Felipe
authors.forename: María
authors.initials: M
authors.lastname: José
authors.forename: Pozuelo
authors.initials: P
authors.lastname: de Felipe
authors.forename: Santiago
authors.initials: S
authors.lastname: Angulo
authors.forename: María-Isabel
authors.initials: MI
authors.lastname: Morosini
authors.forename: Daniel
authors.initials: D
authors.lastname: Bravo
authors.forename: Fernando
authors.initials: F
authors.lastname: Baquero
authors.forename: Rosa
authors.initials: R
authors.lastname: del Campo
mesh_terms: D000328:Adult; D015169:Colony Count, Microbial; D018592:Cross-Over Studies; D004311:Double-Blind Method; D004587:Electrophoresis, Agar Gel; D005243:Feces / Q000382:microbiology; D005260:Female; D005511:Food Handling / Q000379:methods*; D005516:Food Microbiology; D041981:Gastrointestinal Tract / Q000382:microbiology*; D006358:Hot Temperature; D006801:Humans; D048668:Lactobacillus delbrueckii / Q000235:genetics / Q000254:growth & development*; D008297:Male; D016133:Polymerase Chain Reaction / Q000379:methods; D019936:Probiotics; D012336:RNA, Ribosomal, 16S / Q000737:chemistry / Q000235:genetics; D048249:Streptococcus thermophilus / Q000235:genetics / Q000254:growth & development*; D015014:Yogurt / Q000382:microbiology*
chemical_list: D012336:RNA, Ribosomal, 16S