Enterococcus species identified by MALDI-TOF MS in milk from dairy cow mastitis cases and herd surveys

Enterococcus species are increasingly recognized as mastitis pathogens in dairy cows. Reliable species information is required for correctly defining the regional epidemiology of enterococcal mastitis, establishing its relationships with management variables, and understanding its impact on udder health. We investigated the species distribution of enterococci in bovine milk from subclinical mastitis (SCM) and clinical mastitis (CM) cases and full herd surveys (HS) using MALDI-TOF MS as identification method. A total of 21,864 milk samples from 106 dairy herds were routinely collected and analyzed according to the National Mastitis Council (NMC) guidelines over one year. Enterococcus spp. were found in 4.86% of CM, 5.05% of SCM, and 1.37% of HS milk samples. Overall, E. saccharolyticus was the most prevalent species (55.65%), followed by E. faecium (27.25%), and E. cecorum (5.51%), which showed a significant association with SCM (p-value = 0.0128). This study provides novel data on the Enterococcus species distribution in full herds survey and mastitis cases, highlighting the relevance of MALDI-TOF MS in refining enterococcal mastitis epidemiology, as true prevalence and species distribution may have been skewed by conventional biochemical tests.