Short communication: methicillin-resistant staphylococcus aureus detection in US bulk tank milk

Virgin, J.E., Van Slyke, T.M., Lombard, J.E. and Zadoks, R.N. (2009) Short communication: methicillin-resistant staphylococcus aureus detection in US bulk tank milk. Journal of Dairy Science, 92(10), pp. 4988-4991. (doi: 10.3168/jds.2009-2290)

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Staphylococcus aureus is a major cause of mastitis in dairy cattle. This study estimated the herd prevalence of methicillin-resistant Staph. aureus (MRSA) among US dairy herds by testing bulk tank milk (BTM) samples using genotypic and phenotypic methods. A nationally representative sample of 542 operations had BTM cultured for Staph. aureus, and 218 BTM samples were positive upon initial culture. After 4 wk to 4 mo of frozen storage, 87% of 218 samples (n = 190) were still culture positive for Staph. aureus on blood agar, but none were positive for MRSA on the selective indicator medium CHROMagar MRSA. A duplex PCR was used to detect the Staph. aureus-specific nuc gene and the methicillin resistance gene, mecA, in mixed staphylococcal isolates from the 190 BTM samples that were positive for Staph. aureus after storage. Seven samples tested positive for nuc and mecA, and 2 samples tested positive for mecA only. MecA-positive Staphylococcus spp., but not MRSA, were subsequently isolated from 5 samples, whereas neither mecA-positive Staphylococcus spp. nor MRSA was isolated from the remaining 4 samples. Presence of methicillin-resistant, coagulase-negative Staphylococcus spp. may complicate the detection of MRSA by means of PCR on BTM. Bulk tank milk in the United States is not a common source of MRSA.

Item Type:Articles
Glasgow Author(s) Enlighten ID:Zadoks, Professor Ruth
Authors: Virgin, J.E., Van Slyke, T.M., Lombard, J.E., and Zadoks, R.N.
College/School:College of Medical Veterinary and Life Sciences > School of Biodiversity, One Health & Veterinary Medicine
Journal Name:Journal of Dairy Science
Publisher:Elsevier Inc.

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