Persistence of coagulase negative staphylococcal intramammary infections in dairy goats

The objectives of the research described here were to describe the persistence of intramammary infections (IMI) caused by coagulase negative staphylococci (CNS) in goats using strain-typing, and to evaluate the relationship between species-specific CNS IMI and somatic cell score (SCS) at the udder-half level. Udder-half milk samples were collected from all 909 lactating goats (1817 halves; 1 blind half) in a single herd. Milk samples were cultured on Columbia blood agar, and 220 goats with at least one half yielding a single colony type CNS were enrolled for two additional half-level samplings at approximately 1-month intervals. Isolates were identified to the species level by matrix-assisted laser desorption-ionisation time-of-flight mass spectrometry or PCR amplification and partial sequencing of tuf or rpoB. An IMI was defined as persistent when ≥1 follow-up sample yielded the same species and strain as on Day 0 based on pulsed-field gel electrophoresis. A generalised mixed linear model was used to evaluate the odds of persistence as a function of CNS species. A mixed linear model was used to evaluate the relationship between IMI status on a given day and SCS. Among 192 IMI, 69.8% were persistent based on species and strain-type. Staphylococcus simulans IMI had higher odds of persistence than Staphylococcus arlettae IMI. In primiparous goats, Staphylococcus epidermidis IMI was associated with higher SCS than S. arlettae, Staphylococcus xylosus and 'other CNS' IMI. The differences detected in the present study between CNS species, with regard to persistence of IMI and association with SCS, highlight the need to study CNS at the species and strain level to understand the pathogenicity and epidemiology of CNS in goats.