Diagnostic and epidemiological studies of staphylococci in bovine mastitis

Abstract: Diagnostic and epidemiological studies of staphylococci in bovine mastitis.Mastitis is the most common disease in dairy cows and is often caused by staphylococcal infections. The genus Staphylococcus is divided in coagulase-negative (CNS) and coagulase-positive (CPS) staphylococci. The CPS S. aureus is the most prevalent udder pathogen in Swedish dairy cows. For successful mastitis control accurate diagnostics and good understanding of the bacterial epidemiology is essential. This thesis describes methods for species differentiation within CNS and CPS, examines genotypic diversity of S. aureus isolates within Sweden, and identifies potential sources of S. aureus in herds with mastitis problems. First, three phenotypic tests (P-agar with acriflavin, β-galactosidase, and haemolytic reaction in chocolate agar) of eight biochemical tests evaluated were found useful for differentiation between the CPS species, S. aureus, S. hyicus and S. intermedius. The proportions of each species among bovine milk isolates were 97%, 1%, and 2%, respectively. Then, species identification of CNS using the Staph-Zym™ test was compared with sequencing of part of the tuf gene. Staph-Zym™ correctly identified 61%, but gave an incorrect species name in 28% of the milk isolates. Supplementary tests were frequently needed when using Staph-Zym™. In the next study, S. aureus isolates from a national survey on acute clinical mastitis were genotyped using pulsed-field gel electrophoresis (PFGE), and 25 pulsotypes (PTs) were identified. Three of the PTss accounted for over 50% of the isolates and were found all over the country. The distribution of PTs was different in the southern region than in the northern and middle regions of the country. Finally, S. aureus PTs in quarter milk samples, body samples (BS), and environment samples (ES) from various animal groups were studied in five herds with S. aureus mastitis problems. Herd differences were found, but all herds had one predominant unique milk PTs. In three farms this PTs was often found in BS and ES of lactating cows, and occasionally in samples from the other groups.