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Potential Body Site Reserviors for Coagulase Negative Staphylococcal Intramammary Infection in Heifers
Coagulase negative staphylococcal (CNS) species are a common cause of subclinical mastitis in dairy heifers. The relationship between body site colonization and intramammary infection (IMI) in heifers is not well understood. The objective of this study was to determine if specific body sites were colonized with the same CNS species and strain type that were causing CNS IMIs in heifers at calving.
Primiparous heifers (n = 100) at the University of Missouri Dairy were studied. Pre-calving samples were collected approximately 14d before expected calving date and included mammary quarter secretions and body site swabbing samples from teats, muzzle, perineum, and inguinal region. Swabbing samples were collected using sterilized electrostatic dusters. At calving, mammary quarter foremilk samples were collected twice, at approximately 3-5 and 7-9 days postpartum, for culture and somatic cell counting. Swabbing samples were mixed with sterile saline and plated on mannitol salt agar. At 24h, plates were read and up to 10 staphylococcal colonies, including at least one of each morphologically distinct type, were saved for characterization. For mammary secretions and milk, 10 µl was plated onto blood agar and primary identification was determined according to the National Mastitis Council guidelines. All staphylococcal isolates were speciated using rpoB gene sequencing and/or matrix-assisted laser desorption ionisation-time of flight mass spectrometry. Strain-typing was done using pulsed-field gel electrophoresis.
The most common CNS species identified in both pre-partum and post-partum mammary secretions was Staphylococcus chromogenes. Other common species identified were S. agnetis and S. simulans. A total of 2357 staphylococcal isolates were recovered from body site samples and 58% (1360/2357) of these isolates have been speciated. After removing species represented more than once per body site sample per heifer, a total of 459 isolates have been characterized. The most commonly identified species from body site samples were S. chromogenes, S. haemolyticus, and S. xylosus. To date, PFGE strain-typing has been completed on all S. chromogenes isolates from five heifers. Multiple strains of S. chromogenes have been identified on all five heifers. Staphylococcus chromogenes strains isolated from the mammary gland were found to be 100% similar to a teat skin isolate on 3/5 heifers, to an inguinal isolate on 1/5 heifers, and to a teat skin and inguinal isolate on 1/5 heifers. Final results of this study will further the understanding of the epidemiology of CNS infections in dairy heifers and facilitate future studies aimed at control and prevention of CNS IMI.
Keywords: Heifer, mastitis, Staphylococcus