The Altered Schaedler Flora: Continued Applications of a Defined Murine Microbial Community

Abstract

The gastrointestinal (GI) microbiota forms a mutualistic relationship with the host through complex and dynamic interactions. Because of the complexity and interindividual variation of the GI microbiota, investigating how members of the microbiota interact with each other, as well as with the host, is daunting. The altered Schaedler flora (ASF) is a model community of eight microorganisms that was developed by R.P. Orcutt and has been in use since the late 1970s. The eight microorganisms composing the ASF were all derived from mice, can be cultured in vitro, and are stably passed through multiple generations (at least 15 years or more by the authors) in gnotobiotic mice continually bred in isolator facilities. With the limitations associated with conventional, mono- or biassociated, and germfree mice, use of mice colonized with a consortium of known bacteria that naturally inhabit the murine gut offers a powerful system to investigate mechanisms governing host-microbiota relationships, and how members of the GI microbiota interact with one another. The ASF community offers significant advantages to study homeostatic as well as disease-related interactions by taking advantage of a well-defined, limited community of microorganisms. For example, quantification and spatial distribution of individual members, microbial genetic manipulation, genomic-scale analysis, and identification of microorganism-specific host immune responses are all achievable using the ASF model. This review compiles highlights associated with the 37-year history of the ASF, including descriptions of its continued use in biomedical research to elucidate the complexities of host-microbiome interactions in health and disease.

Keywords: ASF; gnotobiotic; microbiota.

Figure 1.

Morphological features of the ceca from gnotobiotic and conventional mice. Left panel: Representative images of the cecum excised from a germfree (left), a monoassociated (center), or a conventional (right) C3H/HeN mouse. Right panel: Representative images of the cecum excised from an ASF (left) or conventional (right) C3H/HeN mouse.

Figure 2.

Stability and relative abundance of the altered Schaedler flora (ASF) in gnotobiotic C3H/HeN mice bred at Iowa State University between 2005 and 2013. (a) Pie chart representing the relative abundance of the members of the ASF in feces collected and archived in 2005. (b) Pie chart representing the relative abundance of the members of the ASF in feces collected and archived in 2013. The relative distribution of taxonomic classes were determined by 16s ribosomal gene sequence analysis (V4 variable region) on the Illumina MiSeq platform. While the relative abundance of ASF 360 was below limits of detection by species-specific 16s amplicon sequencing, this species was detectable by end-point PCR analysis of contents from the upper GI tract.

Figure 3.

Photomicrograph depicting the use of fluorescent in situ hybridization (FISH) to evaluate the spatial distribution of the altered Schaedler flora (ASF) relative to the mucosal epithelium (DAPI stain - blue) of the proximal colon in a C3H/HeN mouse colonized with the ASF and Escherichia coli. The EUB338-FITC probe (green) was used as a nonspecific probe to detect the ASF with a species-specific Cy3-labeled probe for E. coli (orange).