Metagenomic analysis of the uterine bacterial microbiota in healthy and metritic postpartum dairy cows

At present, many bacterial species are validly known as etiological agents of dairy cattle metritis, yet the vast uncultured fraction has received no attention so far. The purpose of this study was to use culture-independent methods to describe and compare the uterine bacterial composition in healthy and metritic postpartum Holstein dairy cows. Both group-specific 16S ribosomal DNA PCR-denaturing gradient gel electrophoresis (DGGE) and clone library sequencing of broad-range 16S ribosomal DNA PCR revealed differences in the bacterial communities comparing healthy and metritic cows. Bacterial diversity in healthy and metritic uteri was greater and more complex than described previously by traditional culture methods. Sequences were assigned to 5 major groups (Gammaproteobacteria, Firmicutes, Fusobacteria, Bacteroidetes, and Tenericutes) and to uncultured bacteria. Additionally, DGGE suggested the presence of Actinobacteria. Most clone sequences in the metritic status libraries were affiliated with the phylum Fusobacteria. Many components, especially from other phyla, have not previously been isolated from cases of metritis. In the clone libraries from the healthy status dairy cows, Gammaproteobacteria was the most prominent group and most sequences showed high identity with Mannheimia varigena, Pasteurella hemolytica, and members of the phylum Tenericutes. Our data showed that the uterine bacterial community in postpartum dairy cows differed considerably between healthy and metritic cows and described the occurrence of a previously unrecognized extent of this diversity in the bovine intrauterine microbiota.