In vitro iron metabolism and genetic diversity of bovine-associated non-aureus staphylococci
Helena Reydams’ thesis focused on non-aureus staphylococci and closely related mammaliicocci (NASM), which are significant causative agents of intramammary infections in lactating dairy cows, leading to mastitis—an inflammation of the mammary gland. These bacteria encompass a diverse group of 53 species and 28 subspecies, with over 26 species isolated from bovine milk samples worldwide. Their presence is not limited to the mammary gland but extends to various bovine-associated habitats, each with unique NASM distributions. Researchers have identified substantial inter- and intraspecific variations in NASM in terms of udder health, milk yield, virulence, and host interactions, emphasizing their importance to udder health.
The main objectives of her thesis included examining the genetic diversity and iron metabolism of Staphylococcus hominis isolated from different bovine-associated habitats, comparing the distribution and genetic diversity of NASM in composite cow milk and bulk tank milk samples, and phenotypically assessing iron acquisition abilities and their genetic underpinnings in diverse NASM strains.
The research delved into the genetic diversity of S. hominis across various bovine-associated habitats, specifically investigating its ability to extract iron from host iron-binding proteins like ferritin and lactoferrin. Sterile quarter milk samples from healthy lactating cows in a Flemish commercial dairy herd were collected, resulting in the identification of 17 NASM species. Notably, S. hominis isolates from quarter milk exhibited significant ferritin iron utilization for growth recovery, shedding light on their iron acquisition mechanisms. She also evaluated the distribution of NASM in composite cow milk (CCM) and bulk tank milk (BTM) samples, emphasizing the importance of considering NASM species at the strain-level. The study revealed varying prevalence of NASM species across herds, highlighting herd-specific NASM distribution patterns. Finally, her research focused on the iron acquisition abilities of bovine NASM, particularly S. chromogenes (traditionally classified as host-adapted) and S. equorum (traditionally classified as environmental). Field strains of these species isolated from CCM and BTM samples were examined, revealing that S. chromogenes strains effectively utilized ferritin for growth recovery in iron-poor conditions, while S. equorum exhibited limited ability to acquire iron due to genomic differences.
In summary, this PhD thesis contributes significantly to our understanding of NASM and their role in bovine mastitis, particularly in terms of genetic diversity, iron acquisition mechanisms, and distribution patterns.
Dr. Helena Reydams, born in 1992 in Berkeley, California, USA, to Belgian parents, spent her formative years in South Bend, Indiana, USA. In 2011, she graduated magna cum laude from her secondary school. After completing her secondary education while working part-time in a small animal clinic as an assistant, she attended Michigan State University (USA) for 2 years as an undergrad pre-vet student with a focus on animal husbandry. Her determination to continue her studies in veterinary medicine led her to Belgium, where she received her Master of Science in Veterinary Medicine from Ghent University in 2019 with distinction, focusing on ruminants. Following her studies, Helena embarked on a doctoral program, “Doctor of Veterinary Medicine,” at the “Mastitis and Milk Quality Research Unit” of the Department of Internal Medicine, Reproduction, and Population Medicine, under the guidance of Prof. dr. Sarne de Vliegher and Prof. dr. Freddy Haesebrouck and received her doctoral degree in 2023. She currently serves as project manager responsible for coordinating the initiation and oversight of an animal welfare label (‘Beter Voor Dieren’) in Flanders, Belgium for farm animals.
