Estado Actual de las Huertas Institucionales

1.4.6.1. Influence of diet on faecal bifidobacterial flora

It is often reported that the compositions of intestinal flora are influenced by diet. The quality of diet can immensely affect human health preventing and reducing susceptibility to particular diseases (Kolida et al., 2000; Gibson, 1999). The physical and physiological characteristics of the gastrointestinal tract and its epithelial layer are greatly affected by the presence of a complex microflora whose density varies according to the section of the intestine colonized. The sensitivity of intestinal microorganisms to gastric acid and oxygen largely determines the sites of colonization. Since the oxidation-reduction potential (Eh) varies according to the microbial population level, the microflora itself controls certain aspects of its own environment. Some facultatively anaerobic groups of bacteria, such as the lactobacilli, streptococci and coliform bacteria, are ubiquitous and are distributed throughout most of the tract. Obligately anaerobic bacteria such as Bacteroides and Bifidobacterium are confined to parts of the gut where Eh values are very low. Such sites include the colon, caecum and the rumen or rumen-like anatomical modifications of the stomach in those animals possessing a fore-gut microbial fermentation.

Although diet is important in determining the qualitative and quantitative composition of the intestinal microflora, it is difficult to demonstrate experimentally. While the adult flora is characteristic of the host species, that of the neonatal mammal is common to a wide range of species since the milk diet produces a common environment in the gut. Characteristic of the gut flora of neonates are low numbers of potentially pathogenic species such as E. coli. These low numbers are maintained by the inhibitory effects of specific antibody (mainly IgA) and several non-specific factors including the iron binding protein, lactoferrin.

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Because of the complex intestinal flora, adult animals are normally extremely difficult to infect with enteric pathogens. Disturbance or removal of the flora (for example by antibiotics) thus increases susceptibility to colonisation by these organisms. An additional consequence of oral antibiotic administration is that commensal and pathogenic bacteria may become resistant to these drugs by mutation or by transferable drug resistance. Both these problems are of considerable significance to animal and public health. Because of this renewed attempts are being made to induce changes in the intestinal flora of animals and man, beneficial to host health, by feeding normal constituents of the gut flora or fermented milk products.

The faecal flora of nine rural healthy Japanese and eight urban healthy Canadians were compared (Benno et al., 1986). The two populations are typical Japanese and Western diets, respectively. The numbers of eubacteria, bifidobacteria, lactobacilli and veilloneallae and the frequency of occurrence of bifidobacteria were higher in the Japanese than in the Canadians. Higher numbers of bacteroides and C. perfringens were found in the Canadians. Presented in Table 1.11. is the faecal flora of vegetarian and non-vegetarian Seventh Day Adventists comparing the faecal flora of volunteers consuming high- and low-beef diets.

Chapter 1 ______________________________________________________________________________ 43 Table 1.11. Faecal microbiota in various dietary groups including seventh-day Adventists who were strictly vegetarian, Japanese who consumed an oriental diet that included fish but no beef, and healthy subjects who consumed a Western diet with relatively large quantities of beef (Gibson and Macfarlane, 1995).

Strict vegetarian (13) Japanese (15)c Western (62) Totald (141)

Microorganisms %a Meanb % Mean % Mean % Mean

Bacterioides 100 11.7 93 10.8 100 11.3 99 11.3 Fusobacterium 0 - 40 8.1 24 8.6 18 8.4 Anaerobic Streptococci 8 11.4 60 9.5 32 10.5 34 10.3 Peptococcus 8 11.2 47 9.4 37 10.1 33 10.0 Peptostreptococcus 23 11.1 80 10.2 35 10.2 45 10.1 Ruminococcus 54 10.2 60 10.3 45 10.0 45 10.2 Anaerobic cocci 85 10.3 100 10.7 98 10.6 94 10.7 Actinomyces 31 10.5 0 - 2 5.7 7.8 9.2 Arachnia- propionibacterium 38 10.0 0 - 2 5.5 9.2 8.9 Bifidobacterium 69 10.9 80 9.7 79 10.4 74 10.2 Eubacterium 92 11.0 93 10.6 95 10.6 94 10.7 Lactobacillus 85 11.1 73 9.0 73 9.3 78 9.6 Clostridium 92 9.4 100 9.7 100 10.2 100 9.8 Streptococcus 100 8.6 100 8.7 100 9.1 99 8.9 Gram-negative facultatives 100 8.2 100 9.2 98 8.9 98 8.7 Candida albicans 15 4.9 47 5.6 14 5.4 14.2 5.4 Other yeasts 23 5.6 53 5.8 31 5.2 36.2 5.6 Filamentous fungi 0 - 0 - 3 3.8 3.5 5.9 Bacillus sp. 69 4.2 80 6.2 82 5.0 82.3 5.2 Totale 100 12.6 100 11.8 100 12.2 100 12.2 a

% Positive. bMean count expressed as organisms log10/g dry weight faeces. cNumber of subjects per dietary group. dTotal for all 141 subjects including polyp. Colonic cancer, and vegetarians who consume some meat. eTotal of all microbes detected (including other genera and groups not listed above).

Chapter 1 ______________________________________________________________________________ 44 Table 1.12. below contains the 25 most prevalent bacteria species that are present in the faeces of human subjects.

Table 1.12: The 25 most prevalent bacterial species in the faeces of human subjects consuming a Western diet (109-10 bacteria per gram wet weight) (Gibson and Macfarlane, 1995)

Bacteroides vulgatus Ruminococcus albus Bifidobacterium adolescentis A Bacteroides species, other Bacteroides distasonis Bifidobacterium adolescentis C Bacteroides fragilis Peptostreptococcus

intermedius

Bacteroides clostridiiformis ssp. clostridiiformis

Bacteroides thetaiotaomicron Peptostreptococcus Peptostreptococcus prevotii Peptostreptococcus micros Peptostreptococcus

productus

Bifidobacterium infantis ssp. liberorum

Bacillus species (all) Eubacterium lentum Clostridium indolis Bifidobacterium adolescentis D Facultative streptococci,

other

Enterococcus faecium Eubacterium aerofaciensr Fusobacterium russii Bifidobacterium longum

In summary, it seems that no general agreement exists in regard to whether or not the bifidobacterial flora of individuals on high-meat diets differ from those of individuals on low- meat diets. However, these results, which were obtained using a comprehensive method for cultivating intestinal flora, indicated that a Japanese-style diet is superior to a western-style diet from the viewpoint of bifidobacteria in the intestinal flora.

The characteristics of particular genera commonly found in human faeces are presented in Table 1.13 including metabolic products and metabolic processes.

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Table 1.13: Characteristics of bacterial genera commonly detected in human faeces (Tannock, Genera Characteristic

Bacteroides Gram-negative, nonspore-forming bacilli. Obligate anaerobe. Metabolic products include combinations of acetic, succinic, lactic, formic or propionic acids. If N-butyric acid is produced, isobutyric and isovaleric acids are also present.

Bifidobacterium Gram-positive, nonspore-forming, nonmotile bacilli sometimes club-shaped or spatulated extremities. Obligate anaerobe. Acetic and lactic acids are produced primarily in the molar ratio of 3:2. Glucose is degraded exclusively and characteristically by the fructose-6-phosphate `shunt’ metabolic pathway.

Clostridium Gram-positive bacilli that form endoscopes. Obligate anaerobe.

Enterococcus Gram-positive cocci. Facultative anaerobe. Lancefield group D. Can grow in 6.5% NaCl broth and in broth at pH 9.6.

Eubacterium Gram-positive bacilli, nonspore-forming. Obligate anaerobe. Produces mixtures of organic acids including butyric, acetic and formic acids.

Fusobacterium Gram-negative, nonspore-forming bacilli. Obligate anaerobe. N-butyric acid is produced, but isobutyric and isovaleric acids are not.

Peptostreptococcus Gram-positive cocci. Obligate anaerobe. Can metabolise peptone and amino acids.

Ruminococcus Gram-positive cocci. Obligate anaerobe. Amino acids and peptides are not fermented. Fermentation of carbohydrate produces acetic, succinic and lactic acids, ethanol, carbon dioxide and hydrogen.

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