|Pettengill, James - U.s. Food & Drug Administration (FDA)|
|Gorham, Sasha - U.s. Food & Drug Administration (FDA)|
|Ottesen, Adrea - U.s. Food & Drug Administration (FDA)|
|Van Kessel, Jo Ann|
Submitted to: Frontiers in Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/26/2016
Publication Date: 5/31/2016
Citation: Haley, B.J., Pettengill, J., Gorham, S., Ottesen, A., Karns, J.S., Van Kessel, J.S. 2016. Comparison of microbial communities isolated from feces of asymptomatic Salmonella-shedding and non-Salmonella shedding dairy cows. Frontiers in Microbiology. 7:691.
Interpretive Summary: The Centers for Disease Control estimates that approximately 1.2 illnesses and approximately 450 deaths occur due to non-typhoidal Salmonella annually in the United States. Dairy cattle and their environments are a reservoir for Salmonella and often infected cows do not show clinical signs of disease. Salmonella serovars Kentucky and Cerro are frequently isolated from dairy cows showing no signs of being sick. However, it remains unknown what factors contribute to colonization of the bovine gut by these two serovars. The animal gut contains a very diverse array of bacteria and other microbes but it’s not clear if there is a relationship between the profile of bacterial groups (metagenome) and infection with S. Kentucky or Cerro. To investigate associations between Salmonella status and bacterial diversity, as well as the diversity of the dairy cow hindgut, the 16S rRNA metagenomes of fecal samples from cows on a single dairy farm were sequenced. Two Salmonella-positive cows and two Salmonella-negative cows were selected for each of five sampling dates between 2006 and 2012. A high level of variability was observed between samples, demonstrating that the microbial community profiles of dairy cow hindguts are diverse. Results indicated that there was a significant difference in the microbial diversity associated with sampling year and date but not with Salmonella status. This study shows that commensal Salmonella infections in dairy cows have little or no impact on the abundance of major bacterial groups in the gut. This information helps scientists and regulatory agencies to further understand the impact of Salmonella infection in dairy cows.
Technical Abstract: In the United States, Salmonella enterica subsp. enterica serotypes Kentucky and Cerro are frequently isolated from asymptomatic dairy cows. However, factors that contribute to colonization of the bovine gut by these two serotypes have not been identified. To investigate associations between Salmonella status and bacterial diversity, as well as the diversity of the microbial community in the dairy cow hindgut, the bacterial and archaeal communities of fecal samples from cows on a single dairy farm were determined by high-throughput sequencing of 16S rRNA gene amplicons. Fecal grab samples were collected from two Salmonella-positive cows and two Salmonella-negative cows on five sampling dates (n = 20 cows), and 16S rRNA gene amplicons from these samples were sequenced on the Illumina MiSeq platform. A high level of alpha (within) and beta diversity (between) samples demonstrated that microbial profiles of dairy cow hindguts are quite diverse. To determine whether Salmonella presence, sampling year, or sampling date explained a significant amount of the variation in microbial diversity, we performed constrained ordination analyses (distance based RDA) on the unifrac distance matrix produced with QIIME. Results indicated that there was not a significant difference in the microbial diversity associated with Salmonella presence (P > 0.05), but there were significant differences between sampling dates and years (Pseudo-F= 2.157 to 4.385, P < 0.05). Based on these data, it appears that commensal Salmonella infections with serotypes Cerro and Kentucky in dairy cows have little or no association with changes in the abundance of major bacterial groups in the hindgut. Rather, our results indicated that temporal dynamics and other undescribed parameters associated with them were the most influential drivers of the differences in microbial diversity and community structure in the dairy cow hindgut.