Daily dietary probiotic supplementation for 6 months was a safe effective way to reduce fever, rhinorrhea, and cough incidence and duration and antibiotic prescription incidence, as well as the number of missed school days attributable to illness, for children 3 to 5 years of age.

Escherichia coli O157:H7 was adapted to acid by culturing for one to two doublings at pH 5.0. Acid-adapted cells had an increased resistance to lactic acid, survived better than nonadapted cells during a sausage fermentation, and showed enhanced survival in shredded dry salami (pH 5.0) and apple cider (pH 3.4). Acid adaptation is important for the survival of E. coli O157:H7 in acidic foods and should be considered a prerequisite for inocula used in food challenge studies. Since 1982, food-related diarrheal outbreaks caused by highly virulent strains of enterohemorrhagic Escherichia coli O157:H7 have been recognized in the United States (11, 16, 20). Enterohemorrhagic strains of E. coli produce Shiga-like toxins, and infections caused by E. coli O157:H7 can result in death, particularly in young children and the elderly (11, 20). Various foods have been implicated in outbreaks, including ground beef, raw milk, apple cider (2, 3, 11, 16, 19, 20), and most recently fermented hard salami (4). Since salami and apple cider rely in part on fermentation and acidity for microbial stability and safety, we were interested in determining if adaptation to acid (6, 12) would affect survival in these low-pH foods. Several investigators have studied acid tolerance and survival of E. coli O157:H7 in broth and food systems (1, 15, 21, 22). In these studies, acid tolerance was determined, but cells were not adapted by growing them at low pH as is required for acid adaptation of Salmonella typhimurium (6, 7, 9). In S. typhimurium, acid adaptation appears to be distinctly different from acid tolerance. However, in E. coli, habituation to normal lethal acidity is induced in stationary-phase cells (12) or by prior growth of E. coli at a sublethal pH value (9). The survival of stationary-phase cells at extremely low pH is termed acid resistance or acid tolerance. Growth pH does not affect the stationary-phase acid resistance of wild-type cells but instead involves the expression of genes mediated by the alternative sigma factor 38 (12, 17, 18). Sigma 38 is not expressed during adaptation during growth at sublethal pHs. Acid adaptation and tolerance have been studied most extensively in S. typhimurium (5, 6, 7, 12), but these characteristics probably also occur in other enteric bacteria, including E. coli and Shigella flexneri (9, 17, 18). We previously showed that acid adaptation increased the resistance of Salmonella spp. to various organic acids and also greatly increased their survival in certain foods (13). Acid adaptation induced cross-protection against environmental stresses that may be encountered during food processing, including heat, salt, an activated lactoperoxidase system, and surface-active agents (14). We investigated the biochemical

The relationship of acid adaptation to tolerance of other environmental stresses was examined in Salmonela typhimurium. S. typhimurium was adapted to acid by exposing the cells to mildly acidic conditions (pH 5.8) for one to two cell doublings. Acid-adapted cells were found to have increased tolerance towards various stresses including heat, salt, an activated lactoperoxidase system, and the surface-active agents crystal violet and polymyxin B. Acid adaptation increased cell surface hydrophobicity. Specific outer membrane proteins were induced by acid adaptation, but the lipopolysaccharide component appeared to be unaltered. These results show that acid adaptation alters cellular resistance to a variety of environmental stresses. The mechanism of acid-induced cross-protection involved changes in cell surface properties in addition to the known enhancement of intracellular pH homeostasis.

Bifidobacteria are important members of the human gut flora, especially in infants. Comparative genomic analysis of two Bifidobacterium animalis subsp. lactis strains revealed evolution by internal deletion of consecutive spacer-repeat units within a novel clustered regularly interspaced short palindromic repeat locus, which represented the largest differential content between the two genomes. Additionally, 47 single nucleotide polymorphisms were identified, consisting primarily of nonsynonymous mutations, indicating positive selection and/or recent divergence. A particular nonsynonymous mutation in a putative glucose transporter was linked to a negative phenotypic effect on the ability of the variant to catabolize glucose, consistent with a modification in the predicted protein transmembrane topology. Comparative genome sequence analysis of three Bifidobacterium species provided a core genome set of 1,117 orthologs complemented by a pan-genome of 2,445 genes. The genome sequences of the intestinal bacterium B. animalis subsp. lactis provide insights into rapid genome evolution and the genetic basis for adaptation to the human gut environment, notably with regard to catabolism of dietary carbohydrates, resistance to bile and acid, and interaction with the intestinal epithelium. The high degree of genome conservation observed between the two strains in terms of size, organization, and sequence is indicative of a genomically monomorphic subspecies and explains the inability to differentiate the strains by standard techniques such as pulsed-field gel electrophoresis.

Objective. To assess the impact of Bifidobacterium lactis HN019 supplementation on whole gut transit time (WGTT) and frequency of functional gastrointestinal (GI) symptoms in adults. Material and methods. We randomized 100 subjects (mean age: 44 years; 64% female) with functional GI symptoms to consume a proprietary probiotic strain, B. lactis HN019 (Fonterra Research Centre, Palmerston North, New Zealand), at daily doses of 17.2 billion colony forming units (CFU) (high dose; n = 33), 1.8 billion CFU (low dose; n = 33), or placebo (n = 34) for 14 days. The primary endpoint of WGTT was assessed by X-ray on days 0 and 14 and was preceded by consumption of radiopaque markers once a day for 6 days. The secondary endpoint of functional GI symptom frequency was recorded with a subject-reported numeric (1–100) scale before and after supplementation. Results. Decreases in mean WGTT over the 14-day study period were statistically significant in the high dose group (49 ± 30 to 21 ± 32 h, p < 0.001) and the low dose group (60 ± 33 to 41 ± 39 h, p = 0.01), but not in the placebo group (43 ± 31 to 44 ± 33 h). Time to excretion of all ingested markers was significantly shorter in the treatment groups versus placebo. Of the nine functional GI symptoms investigated, eight significantly decreased in frequency in the high dose group and seven decreased with low dose, while two decreased in the placebo group. No adverse events were reported in any group. Conclusions. Daily B. lactis HN019 supplementation is well tolerated, decreases WGTT in a dose-dependent manner, and reduces the frequency of functional GI symptoms in adults.