Effect of chitosan microparticles on the uterine microbiome of dairy cows with metritis.

The objective was to evaluate the effect of chitosan microparticles on the uterine microbiome of cows with metritis. Dairy cows with metritis (n = 89) were assigned to 1 of 3 treatments: chitosan microparticles (n = 21) = intrauterine infusion of chitosan microparticles at metritis diagnosis (D0), D2 and D4; ceftiofur (n = 25) = subcutaneous injection of ceftiofur on D0 and D3; Untreated (n = 23) = no treatment. Non-metritic (n = 20) = healthy cows matched by days postpartum at metritis diagnosis. Uterine swabs collected on D0, D3, D6, D9, and D12 were used for 16S rRNA gene sequencing and qPCR quantification. Principal coordinate analysis showed that the microbiome of the ceftiofur-treated and metritic untreated groups progressed towards the non-metritic group by D3, whereas the chitosan microparticles-treated remained unchanged. The differences on D3 were mainly due to a greater relative abundance of Fusobacteria, particularly Fusobacterium in the chitosan microparticles-treated compared with the ceftiofur-treated and metritic untreated groups. Furthermore, the microbiome of the ceftiofur-treated group became similar to the non-metritic group by D9; whereas the chitosan microparticles-treated and metritic untreated groups only became similar to the non-metritic group by D12. The chitosan microparticles treatment resulted in greater total bacterial 16S rRNA gene counts than the metritic untreated controls on D6 and D9, whereas the ceftiofur treatment was the only group that became similar to the non-metritic group by D12. In summary, chitosan microparticles slowed the progression towards a healthy uterine microbiome, whereas ceftiofur hastened the progression towards health.IMPORTANCE Third-generation cephalosporins such as ceftiofur are commonly used to treat metritis in dairy cows. Chitosan microparticles has been shown to have a broad spectrum of activity in vitro and to be effective against uterine pathogens in vivo; therefore, it has been hailed as a possible alternative to traditional antibiotics. Nonetheless, herein we saw that chitosan microparticles slowed the progression of the uterine microbiome of cows with metritis towards a healthy uterine microbiome, whereas ceftiofur treatment hastened the progression towards a healthy uterine microbiome. Given the lack of an effective alternative to traditional antibiotics and an increased concern about antimicrobial resistance, a greater effort should be devoted to the prevention of metritis in dairy cows.