Exploring associations between the teat apex metagenome andStaphylococcus aureusintramammary infection risk in primiparous cows under organic directives

Abstract

ABSTRACTThe primary objective of this study was to identify associations between teat apex microbiome andStaphylococcus aureusintramammary infection (IMI) risk in primiparous cows during the first 5 weeks after calving. We performed a case-control study using shotgun metagenomics of the teat apex and culture-based milk data collected longitudinally from 710 primiparous cows on 5 organic dairy farms. We observed a strong association betweenS. aureusDNA in the metagenomic teat apex data prior to parturition and the odds ofS. aureusIMI after parturition (OR = 38.9, 95% CI: 14.84-102.21). Differential abundance analysis confirmed this association, with cases having a 23.8 higher log fold change (LFC) in abundance ofS. aureusin their samples compared to controls. Of the most prevalent microorganisms in controls, those associated with a lower risk of post-calvingS. aureusIMI includedMicrobacteriumphage Min 1 (OR = 0.37, 95% CI: 0.25-0.53),Corynebacterium efficiens(OR = 0.53, 95% CI: 0.30-0.94),Kocuria polaris(OR = 0.54, 95% CI: 0.35-0.82),Micrococcus terreus(OR = 0.64, 95% CI: 0.44-0.93) andDietzia alimentaria(OR = 0.45, 95% CI: 0.26-0.75). Microcin B17 was the most prevalent antibacterial peptide on the teat apex of cases and controls (99.7% in both groups). The predicted abundance of Microcin B17 was also higher in cases compared to controls (LFC 0.26). Cow and farm random effects often explained a large proportion of the observed variability in the teat apex microbiome, suggesting that our results need to be interpreted within the context of the random effects.IMPORTANCEIntramammary infections (IMI) caused byStaphylococcus aureusremain an important problem for the organic dairy industry. The microbiome on the external skin of the teat apex may play a role in mitigatingS. aureusIMI risk, in particular the production of antimicrobial peptides (AMPs) by commensal microbes. However, current studies of the teat apex microbiome utilize a 16S approach, which precludes detection of genomics features such as AMPs. Therefore, further research using a shotgun metagenomic approach is needed to understand what role pre-partum teat apex microbiome dynamics play in IMI risk.