Abstract
Coagulase-negative staphylococci (CNS) are in several countries the most common bacteria isolated in subclinical mastitis. To investigate the innate immune response of cows to infections with two common mastitis-causing CNS species, Staphylococcus epidermidis and Staphylococcus simulans, experimental intramammary infection was induced in eight cows using a crossover design. The milk somatic cell count (SCC), N-acetyl-β-D-glucosaminidase (NAGase) activity, milk amyloid A (MAA), serum amyloid A (SAA) and proinflammatory cytokines interleukin (IL)-1β, IL-8, and tumor necrosis factor α (TNF-α) were determined at several time points before and after challenge. All cows became infected and showed mild to moderate clinical signs of mastitis. The spontaneous elimination rate of the 16 infections was 31.3%, with no difference between species. Infections triggered a local cytokine response in the experimental udder quarters, but cytokines were not detected in the uninfected control quarters or in systemic circulation. The innate local immune response for S. simulans was slightly stronger, with significantly higher concentrations of IL-1β and IL-8. The IL-8 response could be divided into early, delayed, or combined types of response. The CNS species or persistency of infection was not associated with the type of IL-8 response. No significant differences were seen between spontaneously eliminated or persistent infections.
Highlights
Coagulase-negative staphylococci (CNS) have become more important as bovine mastitis causing agents during recent years
The most common CNS species isolated in mastitis are S. chromogenes, S. epidermidis, S. haemolyticus, S. simulans and S. xylosus [5,6,7]
If the infection persisted over the first experimental period, the infected quarter was treated with an intramammary antibiotic at the beginning of the wash-out period (S. simulans with Carepen® 600 mg procaine penicillin G (Vetcare Oy, Mäntsälä, Finland) and S. epidermidis with Wedeclox mastitis® 1000 mg cloxacillin (WDT, Garbsen, Germany), both once a day for three days), and clearance of the infection was confirmed with bacteriological examination of a milk sample on three consecutive days on days 11, 12 and 13 after treatment
Summary
Coagulase-negative staphylococci (CNS) have become more important as bovine mastitis causing agents during recent years. CNS are the most frequently isolated micro-organisms in bovine intramammary infections (IMI) in many countries [1,2]. The proportion of CNS is especially high in subclinical mastitis [3,4]. The most common CNS species isolated in mastitis are S. chromogenes, S. epidermidis, S. haemolyticus, S. simulans and S. xylosus [5,6,7]. CNS cause mild clinical or subclinical mastitis [8]. CNS species may differ in their pathogenicity, but very little is known about their virulence factors or the immune response in IMI. The duration of CNS IMI varies: infection may be spontaneously eliminated or persist over the entire lactation [10]
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