LAUSR

Abstract Objective of the present work was the investigation of anti-poly-N-acetyl b-1,6 glucosamine (PNAG) staphylococcal antibodies in ewes and the study of factors that may be associated with these. During a field investigation in subclinical mastitis in Greece, milk samples for bacteriological and cytological examination for detection of staphylococcal mastitis and blood samples for detection of anti-PNAG antibodies were collected from 355 ewes in 71 flocks. Prevalence of seropositivity was higher among ewes vaccinated against staphylococcal mastitis (0.750) than non-vaccinated ones (0.458). Mean antibody titres in samples from vaccinated ewes (13.64) were significantly higher than in samples from non-vaccinated ones (7.39). There was no association between identity of staphylococcal isolates recovered from milk samples and antibody titres in blood samples from respective ewes. Among vaccinated ewes, there was correlation (r = 0.922) between total number of genes relevant to biofilm-formation in mastitis staphylococcal isolates and antibody titres in blood samples from respective ewes; further, isolates from ewes with seropositive samples had higher median number of genes (4) than isolates from ewes with seronegative samples (3). In a multivariable mixed-effects model, vaccination emerged as the only significant factor for the prevalence of seropositivity of anti-PNAG antibody titres; when only unvaccinated ewes were included in the model, no factor was found of significance for that prevalence.