Variations in the anaerobic faecal flora of ten healthy human volunteers with special reference to the Bacteroides fragilis-group and Clostridium difficile

In vitro catabolism of 3',4'-dihydroxycinnamic acid by human colonic microbiota

3',4'-Dihydroxycinnamic acid (aka caffeic acid) is a common dietary component found in a variety of plant-derived food products either in a free form or esterified as in chlorogenic acids such as 5-O-caffeoylquinic acid. The dihydroxycinnamate is produced principally by hydrolysis in the colon of 5-O-caffeoylquinic acid and other caffeoylquinic acid esters, and is catabolised by the resident microbiota prior to absorption. In the present study 3',4'-dihydroxycinnamic acid was incubated in vitro, with or without glucose, under anaerobic conditions with faecal slurries obtained from five volunteers. The main resultant catabolites to accumulate were 3-(3',4'-dihydroxyphenyl)propanoic acid (aka dihydrocaffeic acid), 3-(3'-hydroxyphenyl)propanoic acid and phenylacetic acid. Both the rate of degradation of the hydroxycinnamate substrate and the catabolite profile varied between the faecal samples from the individual volunteers. Overall there was no clear cut effect when glucose was added to incubation medium.

Pattern extraction of structural responses of gut microbiota to rotavirus infection via multivariate statistical analysis of clone library data

This study developed a new statistical strategy for analyzing clone library data to observe whether there is a defined pattern in structural responses of gut microbiota to environmental perturbations. A large clone library of genus Bacteroides was constructed with fecal samples for each subject in rotavirus-infected (Group R) and healthy children (Group H). In all, 665 clones of the 12 Group H subjects and 284 clones of the nine Group R subjects were sequenced and classified into 34 operational taxonomic units (OTUs) with a similarity cutoff at 98%. Partial least squares-discriminant analysis was used to observe the change of the Bacteroides spp. composition caused by rotavirus infection and to identify the most relevant species contributing to this shift. It was revealed that H subjects and R subjects were well separated. Bacteroides vulgatus, Bacteroides stercoris and Bacteroides fragilis were identified as the most important discriminating OTUs between two groups. The increased abundance of B. fragilis and the decreased populations of B. vulgatus and B. stercoris in infected guts observed in this study were in agreement with previous culture-based studies. The strategy developed in this work can be used to reveal patterns in structural responses of gut microbiota to environmental perturbations from large-scale 16S rRNA gene-based sequencing data.

Comparison of compositions and metabolic activities of fecal microbiotas in young adults and in antibiotic-treated and non-antibiotic-treated elderly subjects

The colonic microbiota mediates many cellular and molecular events in the host that are important to health. These processes can be affected in the elderly, because in some individuals, the composition and metabolic activities of the microbiota change with age. Detailed characterizations of the major groups of fecal bacteria in healthy young adults, in healthy elderly people, and in hospitalized elderly patients receiving antibiotics were made in this study, together with measurements of their metabolic activities, by analysis of fecal organic acid and ammonia concentrations. The results showed that total anaerobe numbers remained relatively constant in old people; however, individual bacterial genera changed markedly with age. Reductions in numbers of bacteroides and bifidobacteria in both elderly groups were accompanied by reduced species diversity. Bifidobacterial populations in particular showed marked variations in the dominant species, with Bifidobacterium angulatum and Bifidobacterium adolescentis being frequently isolated from the elderly and Bifidobacterium longum, Bifidobacterium catenulatum, Bifidobacterium boum, and Bifidobacterium infantis being detected only from the healthy young volunteers. Reductions in amylolytic activities of bacterial isolates in healthy elderly subjects and reduced short-chain fatty acid concentrations supported these findings, since bifidobacteria and bacteroides are important saccharolytic groups in the colon. Conversely, higher numbers of proteolytic bacteria were observed with feces samples from the antibiotic-treated elderly group, which were also associated with increased proteolytic species diversity (fusobacteria, clostridia, and propionibacteria). Other differences in the intestinal ecosystem in elderly subjects were observed, with alterations in the dominant clostridial species in combination with greater numbers of facultative anaerobes.

Micromorphometrical analysis of rodent related (SPF) and unrelated (human) gut microbial flora in germfree mice by digital image processing

Digital image processing (DIP) of bacterial smears is a new method of analysing the composition of the gut microbial flora. This method provides the opportunity to compare and evaluate differences in the complex highly concentrated anaerobic fraction of gut microbial flora, based on micromorphological differences. There is ample evidence that this fraction can be characterized as related or unrelated to the host organism by its immunogenicity. In this study germfree ND2 mice were associated with either related (rodent) SPF microflora (SPF-MF) or unrelated human MF (HUM-MF). DIP analysis was performed on original SPF-MF and HUM-MF and on the faeces of ex-germfree mice 4 weeks after association. The micromorphological pattern of highly concentrated anaerobic bacteria in faeces of HUM-MF associated ex-germfree mice was significantly different from SPF-MF associated counterparts with regard to the scores for elongation (P < 0.01) and morphological variety (P < 0.05). Moreover, gross morphological variability was present between individual HUM-MF associated mice but not between individual SPF-MF associated animals. No differences were found between original SPF and HUM-MF. The data are discussed with regard to differences in the presence of (non-)immunogenic bacteria and the ability for related and unrelated flora to colonize the murine gut. This study provides evidence that murine host specificity of microbial flora may not only be reflected in the number of non-immunogenic bacteria but also in the micromorphological pattern of highly concentrated anaerobic bacteria in faeces measured by DIP analysis.

Quantitative fluorescence in situ hybridization of Bifidobacterium spp. with genus-specific 16S rRNA-targeted probes and its application in fecal samples

Three 16S rRNA hybridization probes were developed and tested for genus-specific detection of Bifidobacterium species in the human fecal flora. Variable regions V2, V4, and V8 of the 16S rRNA contained sequences unique to this genus and proved applicable as target sites for oligodeoxynucleotide probes. Determination of the genus specificity of the oligonucleotides was performed by whole-cell hybridization with fluorescein isothiocyanate-labelled probes. To this end, cells were fixed on glass slides, hybridized with the probes, and monitored by videomicroscopy. In combination with image analysis, this allowed quantification of the fluorescence per cell and objective evaluation of hybridization experiments. One of the probes developed was used to determine the population of Bifidobacterium spp. in human fecal samples. A comparison was made with results obtained by cultural methods for enumeration. Since both methods gave similar population estimates, it was concluded that all bifidobacteria in feces were culturable. However, since the total culturable counts were only a fraction of the total microscopic counts, the contribution of bifidobacteria to the total intestinal microflora was overestimated by almost 10-fold when cultural methods were used as the sole method for enumeration.

Variations in concentrations of bacterial metabolites, enzyme activities, moisture, pH and bacterial composition between and within individuals in faeces of seven healthy adults

Variations between and within individuals, and correlations between concentrations of bacterial metabolites, including putrefactive products, ammonia and short chain fatty acids (SCFAs), enzyme activities, moisture and pH, as well as bacterial composition, were studied in faecal samples from seven healthy adults over a period of 7 months. Large variations, both between and within individuals, were observed in concentrations of putrefactive products. Although values for ammonia, SCFAs, enzyme activities, moisture and pH were generally variable, significant person-to-person differences were observed. While ranges of log viable counts of the predominant bacteria such as eubacteria, bifidobacteria and bacteroides in each subject remained between 0.2 and 1.3, those of enterobacteria, streptococci (including enterococci) and lecithinase-negative clostridia varied between 0.4 and 3.0. Levels of bifidobacteria, enterobacteria, streptococci and total aerobic bacteria showed inter-individual variations. Correlations were found among certain of the parameters: moisture correlated negatively with p-cresol (r = -0.707), pH (r = -0.671) and beta-glucosidase activity (GS) (r = -0.608), and positively with acetic acid (r = 0.621), while negative correlations were observed in pH with acetic and butyric acids (r = -0.690 and -0.623, respectively). No significant correlations were found between bacterial compositions, and other faecal factors such as pH, moisture, metabolic enzyme activities and concentrations of putrefactive products.

Healthy individuals possess circulating antibodies against their indigenous faecal microflora as well as against allogenous faecal microflora: an immunomorphometrical study

Healthy persons were shown to possess circulating antibodies of both IgA, IgG and IgM isotype directed against the bacteria of their faecal microflora, assessed by immunomorphometry. After removal, by absorption, of the fraction of antibodies directed against the autochthonous faecal bacteria or cross-reacting with allogenous faecal bacteria, there were still antibodies left directed against allogenous faecal bacteria of both the IgA, IgG and IgM isotype. However, relatively more antibodies of the IgA isotype appeared to be directed against allogenous bacteria than against indigenous faecal bacteria. Persons who reacted with specific antibodies to many bacteria of their own flora also tended to react specifically to bacteria in the allogenous microflora of the other volunteers. The patterns of antibodies directed to faecal bacteria of different morphologies (morphotypes) were unique for each individual.

Low-dose ciprofloxacin for selective decontamination of the digestive tract in human volunteers

The effect on the faecal aerobic and anaerobic flora of ciprofloxacin given in low doses for selective decontamination of the digestive tract was investigated in ten human volunteers. The volunteers received 50, 100 and 200 mg of ciprofloxacin every 12 h for five days at intervals of three and five weeks respectively. No significant differences in the numbers of aerobes or anaerobes were seen after the 2 x 50 mg regime. The colony counts of most anaerobes and the total aerobe count were significantly decreased after the 2 x 100 mg [corrected] regime. Whereas the aerobe count was also significantly decreased after administration of 2 x 200 mg, the anaerobe count remained stable. Clostridium difficile was not detected during or after treatment. From these results it can be concluded that ciprofloxacin in a dose of 2 x 200 mg [corrected] can be recommended for selective decontamination of the digestive tract.