The diversity of coliphages and indigenous coliform strains (ICSs) simultaneously present in horse feces was investigated by culture-based and molecular methods. The richness of coliforms (as estimated by the Chao1 method) is about 1,000 individual ICSs distinguishable by genomic fingerprinting present in a single sample of feces. This unexpectedly high value indicates that some factor limits the competition of coliform bacteria in the horse gut microbial system. In contrast, the diversity of phages active against any selected ICS is generally limited to one to three viral genotypes present in the sample. The sensitivities of different ICSs to simultaneously present coliphages overlap only slightly; the phages isolated from the same sample on different ICSs are usually unrelated. As a result, the titers of phages in fecal extract as determined for different Escherichia coli strains and ICSs may differ by several orders of magnitude. Summarizing all the data, we propose that coliphage infection may provide a selection pressure that maintains the high level of coliform diversity, restricting the possibility of a few best competitors outgrowing other ICSs. We also observed high-magnitude temporal variations of coliphage titers as determined using an E. coli C600 test culture in the same animal during a 16-day period of monitoring. No correlation with total coliform count was observed. These results are in good agreement with our hypothesis.Bacteriophages exert a significant influence on natural microbial communities (2, 24, 33). They are responsible for 20 to 80% of bacterial mortality in freshwater and marine ecosystems (25, 33) and increase bacterial biodiversity (references 14, 15, 31, and 33 and references therein) due to preferential attack on the dominant species or strains and redistribution of the organic matter. The role of bacteriophages could be even more important in microbial systems where high densities of active bacteria are achieved. Among these systems are intestinal microbial populations of animals and humans where bacteria (17, 28) and bacteriophages (5,6,9,10,13,16,17) are present at high densities. The gut is the natural habitat for Escherichia coli and for coliphages, which are highly suitable for work in culture, making this system attractive as a model for phage ecology.For our study, we selected the horse as the macro host. The cellulolytic microbial community localized in the horse large intestine is very complex and includes bacteria, archaea, fungi, and protozoa (18). In contrast to rumen communities, the microbial biomass in the horse intestine is not subjected to digestion and is excreted with the feces. The conditions in the horse gut seem more stable than those in the intestines of many other species, as the time taken to digest grass is about 72 h (18), and the intervals between food intake and defecation are normally much shorter. A spatial complexity is present in the gut (9). The mucosal surface and the lumen contents are different ecological niches for bacteria. It has been show...

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We developed a novel PCR-fingerprinting system for differentiation of enterobacterial strains using a single oligonucleotide primer IS1tr that matches the inverted terminal repeats of the IS1 insertion element. Compared to widely used BOX-PCR and ribotyping methods, our system features higher resolution allowing differentiation of closely related isolates that appear identical in BOX-PCR and ribotyping but differ in their phage sensitivity. The IS1-profiling system is less sensitive to the quality of the material and equipment used. At the same time, BOX-PCR is more universal and suitable for bacterial strain grouping and reconstruction of the low-distance phylogeny. Thus, our system represents an important supplement to the existing set of tools for bacterial strain differentiation; it is particularly valuable for a detailed investigation of highly divergent and rapidly evolving natural bacterial populations and for studies on coliphage ecology. However, some isolates could not be reliably differentiated by IS1-PCR, because of the low number of bands in their patterns. For improvement of IS1-fingerprinting characteristics, we offer to modify the system by introducing the second primer TR8834 hybridizing to the sequence of a transposase gene that is widely spread in enterobacterial genomes. KEYWORDS genomic fingerprinting, whole-cell PCR fingerprinting, insertion element, Enterobacterial diversity, strain differentiation. ABBREvIATIONS IS -insertion sequence, ERIC -enterobacterial repetitive intergenic consensus, REP -repetitive extragenic palindromic sequence, dNTP -deoxyribonucleotide triphosphate, OTUs -operational taxonomic units.