Epidemiology of non-aureus staphylococcal mastitis in dairy goats
[ACCESS RESTRICTED TO THE UNIVERSITY OF MISSOURI AT AUTHOR'S REQUEST.] The hypothesis of this work was that molecular-based speciation and strain-typing methods would help differentiate staphylococcal species with greater potential for persistence of intramammary infection (IMI) or for induction of an inflammatory response of the mammary gland from less pathogenic species. Therefore, the specific objectives of this work included 1) the validation of MALDI-TOF mass spectrometry as a rapid, cost-effective molecular-based method for reliable species identification of staphylococcal isolates, 2) the evaluation of the persistence of intramammary infections (IMI) during lactation and over the dry period using strain-typing, 3) the evaluation of the role of teat skin as a potential reservoir for IMI using strain-typing, 4) the validation of a commercial small ruminant lentivirus (SRLV) competitive ELISA on milk, and 5) the evaluation of the association between SRLV seropositivity, staphylococcal IMI, and milk somatic cell count. MALDI-TOF was shown to have good typeability and excellent accuracy for the identification of staphylococcal species isolated from goat milk. Species causing IMI associated with higher somatic cell score included Staphylococcus chromogenes (goatlevel), and Staphylococcus epidermidis and Staphylococcus simulans (udder-half level). Species that were associated with more persistent IMI were Staphylococcus caprae and S. simulans. Based on frequency of isolation from milk and teat skin, S. epidermidis, S. caprae, S. simulans, and Staphylococcus xylosus were considered as possible udderadapted pathogens, whereas Staphylococcus arlettae, Staphylococcus equorum, and Staphylococcus lentus might be considered either opportunistic or environmental pathogens. Additionally, pre-partum skin colonization by S. caprae was a risk factor for S. caprae IMI at the onset of lactation. Frozen-thawed milk was a suitable alternative substrate to serum for a commercial SRLV competitive ELISA test. Overall, the species most consistently identified as more pathogenic than others were S. caprae, S. simulans, and S. epidermidis.
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