Isolation and Identification of Staphylococcus Species From Mastitic Dairy Cows and Associated Risk Factors in and Around Bahir Dar, Ethiopia

BACKGROUND: Bovine mastitis remains one of the most frequent and costly diseases affecting dairy cattle, with significant impacts on health, welfare, and productivity. Staphylococcus species are among the major pathogens responsible for bovine mastitis, leading to reduced milk yield and posing a potential risk to public health. However, there has been limited research on the specific mastitis-causing pathogens and the risk factors associated with the condition in the study area. Therefore, the objective of this study was to isolate and identify Staphylococcus species associated with bovine mastitis and to assess the risk factors linked to their occurrence. MATERIAL AND METHODS: A cross-sectional study was conducted from October 2022 to December 2023 in the Bahir Dar region to investigate the prevalence and risk factors associated with Staphylococcus species causing mastitis in dairy herds. A total of 150 lactating cows from 21 farms were included in the study, with 592 milk samples collected from the four quarters of each cow. The samples were screened via the California mastitis test and physical examination. Staphylococcus species isolates were performed on Mannitol Salt Agar, followed by biochemical testing to confirm the presence of Staphylococcus species. The STATA version 16 software was used to analyse the results of the study. An odds ratio and 95% CI were computed, and p values (p < 0.05) were considered significant. Multivariable logistic regression analysis was also used to determine the association between risk factors and cow-level mastitis. RESULT: Among the 592 milk samples collected, 119 (20.1%) samples exhibited mastitis in at least one quarter. The overall prevalence of mastitis at the farm, cow, and quarter levels was 90.5%, 48.7%, and 20.1%, respectively. Out of the total quarters examined, 33 quarters (5.5%) were positive for clinical mastitis. At the cow level, 24 cows (16%) showed clinical signs of mastitis. In addition, 86 quarters (14.52%) were positive for subclinical mastitis. At the herd level, 49 cows (32.7%) were affected by subclinical mastitis. Of the 119 mastitis-positive samples, 80 were bacteriologically confirmed to harbour Staphylococcus species. A total of eight different Staphylococcus species were identified. Among these, Staphylococcus chromogenes was the most prevalent isolate (19%), followed by Staphylococcus aureus, Staphylococcus hyicus, and Staphylococcus epidermidis (each 15%), Staphylococcus haemolyticus (11%), Staphylococcus simulans and Staphylococcus xylosus (each 10%), and Staphylococcus intermedius (5%). The risk factors contributing to the prevalence of mastitis were identified as cows' age, lactation length, herd size, parity, and hygienic status, all of which demonstrated statistically significant associations (p < 0.05). CONCLUSIONS: Mastitis caused by Staphylococcus is a significant issue in dairy production within the study area. Several risk factors, including age of the cows, lactation length, herd size, parity, and hygienic status, were found to be significantly associated with the prevalence of mastitis in the cows. While these factors showed a clear correlation with mastitis prevalence, breed and management type did not appear to significantly influence the occurrence of mastitis. Additionally, subclinical mastitis was more commonly observed than clinical mastitis.