Diversity of Staphylococcus aureus associated with mastitis from dairy cows in Rwanda

Staphylococcus aureus is a predominant mastitis pathogen in cows worldwide. Subclinical to clinical and acute to chronic forms are possible and directly impact the welfare and milk yield of animals as well as the quality of the milk. Frequent, too rapid and often prophylactic use of antibiotics, poorer veterinary care, especially in rural areas, and the connection with a lack of hygiene measures, for example during milking, favor the occurrence of mastitis in dairy cows. Frequent consequences are the development of resistance, chronic mastitis, a decline in performance, and a negative impact on human health. A previously conducted study by Antók et al. (2019) focused on the characterization of Staphylococcus species limited to the northern province of Rwanda and Kigali. In general, little information is available on Staphylococcus aureus-associated mastitis in cattle from sub-Saharan Africa. The aim of the current study is to investigate the diversity of Staphylococcus aureus from cows with mastitis at the national level of Rwanda, i.e. all five provinces. A total of 1080 milk samples were collected from different farms across Rwanda. One hundred and thirty-five Staphylococcus aureus isolates were obtained and characterized by antimicrobial susceptibility testing and spa typing. In addition, the presence of the trimethoprim resistance gene dfrG was tested using PCR. Seven clonal complexes were detected, which are CC97, CC3666, CC3591, CC152, CC1, CC130 and CC705. While CC97 was frequently found globally in both mastitis-affected and healthy cows, CC3666 and CC3591 were found exclusively in Rwanda and partly also in neighboring countries. As a complex typically found in humans in Africa, CC152 is becoming increasingly important in these countries, especially since it is also frequently found in bovine isolates. Most of the isolated strains were assigned to CC97, followed by CC3666 and CC3591. Nineteen different spa types were detected. Within CC97, the most common spa type was t9432. Within CC3666, t18853 was identified as the most common spa type, while CC3591 harboured t458. Strains belonging to CC152 presented the spa type t355 and had the dfrG resistance gene. In the present study, isolates associated with bovine mastitis were investigated in all five provinces of Rwanda and the findings support previous studies. Pathogenic Staphylococcus spp. strains in dairy cows able to cause mastitis has far-reaching consequences for the entire dairy industry in Rwanda, including the population, and plays a crucial role in One Health. An understanding of this disease, the antibiotic use and hygiene practices must be improved, and long-term success can be achieved with appropriate medical care and monitoring strategies.