Variation of microbiological and biochemical parameters in the faeces of two healthy people over a 15 day period.

Background: Recent years have seen increasing interest in the complex microbial ecosystem of the human gastrointestinal tract. Knowledge of its microbial colonists and their beneficial/detrimental activities is important. However, generalized assumptions about the microbial composition of the human gut should be taken with caution until more studies in different human communities have been conducted. The capacity of modulating or inhibiting harmful populations through high doses of beneficial microorganisms (probiotics) is now an attractive possibility.

Aims: The aim of this study was to determine the daily variation in the most prominent and representative of the cultivable microbial populations in the faeces of two healthy Spanish persons, with special reference to the lactic acid bacteria (lactobacilli and bifidobacteria). Faecal enzymatic activities caused or modulated by gut microorganisms were also examined.

Methods: Microbial populations were enumerated in selective and differential media. LAB species isolated from MRS agar plates were further identified by phenotypic and genetic techniques. Enzymatic activities were measured by the semi quantitative method of the API ZYM system.

Results: Obligate anaerobes (members of the Clostridium clusters and species of bacteroides and bifidobacteria) made up the largest bacterial populations in both individuals (ranging between 10(10)-10(11) cfu/g of faeces) and remained constant over time. Lactobacilli species were found at an intermediate level (around 10(8) cfu/g), and yeasts and moulds, staphylococci, enterococci, coliforms and Enterobacteriaceae at a lower level (between 10(3) to 10(6) cfu/g). 38 lactic acid bacteria strains identified belonged to Bifidobacterium bifidum [19], Bifidobacterium longum [7], Bifidobacterium adolescentis [7] and Lactobacillus ruminis [5] species. Enzymatic profiles and values were shown to be personal and stable, but inter-sample fluctuations were recorded.

Conclusions: The dominant microbial populations in the faeces of the two persons were similar and stable during the sampling period. Large differences were found in the lactic acid bacterial composition of each individual. Biochemistry seemed to be also personal and stable over time.