Comparison of methods and animal models commonly used for investigation of fecal microbiota: Effects of time, host and gender
Introduction
While many studies address effects of endogenous and exogenous factors on the composition of the gastrointestinal microbiota (Djouzi et al., 1997, Fujiwara et al., 2001, Mai et al., 2004, Macpherson and Harris, 2004, Goossens et al., 2005), only limited data are available on the (unprovoked) variation of intestinal microbiota in animal models. Nevertheless, knowledge about variations in the intestinal microbiota (over time and between individuals) prior to intervention is often an important prerequisite for design and interpretation of cause–effect studies. The rationale for the present study was to provide such knowledge.
The intestinal and fecal microbiota of mammals is dominated by relatively few bacterial divisions, that are highly diverse at the strain/subspecies level (Backhed et al., 2005). Feces contains up to 1012 bacteria per gram (Kleessen et al., 2000), and is estimated to harbor more than 800 different microbial species (Backhed et al., 2005). Comparison of culture-based and molecular methods reveals that only 20–50% of gut microbes can be detected by cultivation (Wilson and Blitchington, 1996, Suau et al., 1999). Therefore, various molecular methods for studies of complex microbial communities have been applied, many of which involve amplification by polymerase chain reaction (PCR) of 16S ribosomal RNA genes from extracted microbial DNA (Tannock, 2001, Zoetendal et al., 2004). Separation and analysis of amplified DNA fragments can be done using e.g., denaturing gradient gel electrophoresis (DGGE) or terminal restriction fragment length polymorphism (T-RFLP) (Zoetendal et al., 2004).
We have used DGGE separation and T-RFLP analysis to study variation over time and between individuals of the fecal microbiota of rats. Additionally, conventional cultivation on selective agars was carried out. We find that our results are relevant for design and interpretation of future studies addressing effects of a given intervention on the fecal microbiota of experimental animals.
Section snippets
Specific pathogen free (SPF) rats
Ten conventional, specific pathogen free (SPF) Sprague–Dawley rats were purchased from Møllegaarden Breeding Centre, Denmark. Animals (six males and four females, aged 9 to 10 weeks at arrival and originating from two litters), were housed and fed as previously described (Schlundt et al., 1994), but were caged individually.
Human flora associated (HFA) rats
Eight germfree Sprague–Dawley rats (four males and four females, aged six months, and originating from a single litter) were used. Rats were bred at the Danish Institute for
Comparison of the fecal microbiota of two animal models
Comparison of SPF and HFA rats by selective plating for five bacterial groups revealed that a higher number of HFA animals had a significant (p < 0.05) variation of the fecal microbiota over time than was observed for SPF animals (Table 1). Variations observed in HFA animals were mainly attributed to fluctuations in total bacterial densities as well as in populations of Enterococcus/Streptococcus, and to a general decrease in the Lactobacillus population over time (Fig. 1).
Comparison of SPF rats
Discussion
Two important prerequisites for studies addressing effects of defined actions/agents on the intestinal microbiota of experimental animal models is (i) knowledge about variation naturally occurring in such models, and (ii) knowledge about the usefulness of the applied methods to detect such variations. While traditional selective plating offers the advantage of rapid sample processing, and direct linking of results to a given bacterial genus or species, molecular methods are needed to
Acknowledgements
This work was financed by the Danish FØTEK 3 program (3401-44-03-691) and The Danish Bacon and Meat Council. The work was conducted in collaboration with Chr. Hansen A/S, Danisco A/S, and the Danish Toxicology Centre. We thank Bodil Madsen and Linda Bergstrøm for excellent technical assistance.
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