Elevated Systemic IL-17A Response in Goats Compared to Sheep with Natural Staphylococcus aureus Mastitis: A Serological and Correlative Analysis

Background:Isolates of Staphylococcus aureus from milk and clinical samples were identified using standard bacteriological and biochemical tests that include Gram staining, catalase tests, and additional slide and tube coagulase tests. This study investigated mastitis in sheep and goats by using microbiological culture and biochemical tests of Staphylococcus aureus isolates. The research focused on IL-17A related to the host’s immune response, specifically measuring serum IL-17A levels with ELISA. Interleukin-17A (IL-17A) is an essential pro-inflammatory cytokine that facilitates the recruitment of neutrophils in the case of bacterial mastitis. The local mammary responses are better understood and documented, whereas the systemic responses with the presence of IL-17A in small ruminant Staphylococcus aureus infections are less documented and studied. Aims: The current study aimed to assess and compare the levels of serum IL-17A in S. aureus mastitis-infected sheep and goats and attempt to find a possible relationship with the microbiological prevalence data. Results:All infected animals had some level of detectable systemic IL-17A. Comparatively, goats had a statistically significant elevation in the concentration of IL-17A (37.14 ± 8.23 pg/mL) versus sheep IL-17A (29.77 ± 6.45 pg/mL) (p < 0.001). Serological IL-17A concentration differences were consistent across raw optical density values (0.356 ± 0.085 vs. 0.167 ± 0.041, p < 0.001) and log-transformed data. It is worth noting that the stronger IL-17A response in goats was associated with a lower prevalence of S. aureus isolation from milk (56% in goats vs. 82% in sheep, χ² = 6.73, p = 0.0094). Conclusion: The S. aureus mastitis infection provokes an identifiable systemic IL-17A response in goats and sheep, with goats exhibiting a considerably more robust Th17 response. The degree of this species-specific immunological difference is likely to affect the course and outcome of an infection, indicating that goats may depend more on IL-17A -mediated mechanisms for bacterial containment.