Non-aureus Staphylococci and related Mammaliicoccal species and their association with udder health in organic dairy cows
Previous studies have suggested that udder health may be impaired on organic dairy farms. However, there is limited knowledge about udder health in dairy cows on organic farms, with prior research primarily addressing herd-level management. This leaves gaps in understanding individual cow-level mastitis pathogen prevalence and dynamics. Given the potential impact of antibiotic restrictions, further research is needed to understand how mastitis pathogens persist in the udder and their relationship with udder health and milk production.
Non-aureus Staphylococci and Mammaliicocci (NASM) have gained attention as potential candidates for mastitis control. Studies have demonstrated the in vitro antimicrobial activity of NASM against mastitis pathogens. However, there is limited understanding of how this activity impacts pathogen colonization and whether it is strain-specific or linked to specific clades within NASM species. This thesis aimed to investigate the dynamics of intramammary infections (IMI) in primiparous cows on certified organic farms, focusing on the relationship between IMI presence, somatic cell count (SCC), and milk production. It also explored the antimicrobial activity of NASM from teat apices and examined their genotypes in cows with and without IMI caused by Staphylococcus aureus or Streptococcus spp. and Streptococcus-like organisms (SSLO).
This investigation included data from 503 first-lactation cows from five organic dairy farms, where we collected and cultured weekly milk samples during the first month of lactation and followed them up to 180 days in milk. Our results showed a high prevalence of Staphylococcus aureus and Streptococcus spp. during early lactation in first-lactation organic dairy cows, with herd-specific differences. A large proportion of these IMI were classified as persistent, identified in the first week after calving, and were associated with an increased risk of subclinical mastitis in the first 180 days in milk. In a subset of animals from two farms, we collected teat apex gauze samples, confirmed the taxonomy of isolates using MALDI-TOF MS, and, for those identified as NASM, performed whole genome sequencing and evaluated their in vitro antimicrobial activity. Teat apices of organic dairy cows around parturition harbored in many cases more than one NASM species and in some instances multiple strains within the same species. NASM isolates with the lowest minimum inhibitory concentrations against Staphylococcus aureus were most common in cows without Staphylococcus aureus or SSLO IMI. All NASM isolates contained genes linked to antimicrobial peptide production, but this did not correlate with their in vitro inhibitory activity. Among NASM species, Staphylococcus succinus exhibited strong inhibitory activity against both Staphylococcus aureus and Streptococcus uberis, with clade-specific effects.
Overall, this research enhances our understanding of the epidemiology of mastitis pathogens in organically managed cows and suggests that NASM may offer protection against mastitis pathogens. However, further research is needed to confirm these results and identify the mechanisms behind NASM’s antimicrobial effects, and the specific peptides involved.
Felipe Peña Mosca was born and raised in Uruguay in a family where his mother is a veterinarian and his family operates a beef cattle farm. Felipe completed his veterinary degree in 2015. After graduation, his interest shifted from beef to dairy production, and he became particularly interested in the population control of infectious diseases, especially mastitis. During this time, he completed his Master’s at the Universidad de la República (Uruguay) and worked at the veterinary college, as well as on dairy farms, focusing on mastitis control. To broaden his skill set, particularly in veterinary epidemiology and data analysis, he moved to the United States in 2019, where he completed his PhD at the University of Minnesota. Felipe is currently working as a Post-doctoral Associate at Cornell University.
