Coagulase-negative staphylococci mastitis in Dutch dairy herds

Mastitis is one of the most important diseases in dairy cattle. Recently, the so-called minor pathogens, of which coagulase-negative staphylococci (CNS) are the most important group of bacteria, has received more attention. This thesis focuses on the role of CNS in udder health of dairy cows. The relevance of CNS is studied in a prevalence study of 49 Dutch dairy herds. Coagulase-negative staphylococci were the most frequently isolated group of bacteria (11% of quarters) and were found in all herds. Control programs such as the “five-point program” seem to be less effective to reduce the prevalence of CNS intramammary infection (IMI). The prevalence of CNS IMI was associated with environmental herd level variables such as source of drinking water not being tap water, housing of dry cows in one group instead of multiple groups, pasturing during the outdoor season, and proportion of stalls contaminated with milk. Identification of CNS at the species level in service laboratories is generally carried out using phenotypic tests. The accuracy of two phenotypic tests, API Staph ID 32 and Staph-Zym, was determined in comparison with identification based on DNA-sequencing. A total of 172 CNS isolates from bovine milk samples were classified into 17 species. The API Staph ID 32 correctly identified 41% and he Staph-Zym 31% of the CNS isolates. Both phenotypic tests were unsuitable for identification of CNS species from bovine milk samples. The effect of CNS on somatic cell count (SCC) of quarter, cow and bulk milk was studied. Quarters with a CNS IMI had a lower SCC than quarters with a major pathogen IMI but a higher SCC than culture-negative quarters. This was also found for composite SCC. Cow-level prevalence of CNS IMI was higher in dairy farms with a BMSCC