OSU Biochemistry and Molecular Biology

Dr. John E. Gustafson




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 Research Tidbits

Where does the work in our laboratory intersect with Agriculture?

      The first methicillin-resistant S. aureus (MRSA) infection was described in 1961, and since then, human infections caused by multidrug-resistant MRSA have become commonplace.

      An association of MRSA and bovine mastitis was first reported in 1972 and MRSA transmission appears to occur between animals as well as from animals to humans. Carriage of MRSA by livestock has been shown to correlate with the MRSA colonization of farm families, veterinarians and healthcare workers.

     Our laboratory recently characterized S. aureus strains isolated from raw milk samples of mastitic and healthy dairy cattle from a Paso Del Norte region dairy. One purpose of the study was to determine if the clonal spread of MRSA strains was occurring in mastitic and healthy dairy cattle. Forty confirmed S. aureus strains were isolated from 29 milk samples out of 133 milk samples analyzed. Molecular epidemiology determined that the 40 S. aureus strains characterized were indeed clonal, meaning they were spreading among the dairy cattle examined. Some strains isolated from cows undergoing antibiotic therapy demonstrated resistance to three or more antimicrobial classes. Roche 454 GS pyrosequencing was used to produce a draft genome sequence of two of the dairy strains, MRSA strain H29 and methicillin-susceptible S. aureus strain PB32. Analysis of the H29 genome demonstrated its tight relationship to a human MRSA strain. Investigation of the H29 genome also revealed exactly why this strain is resistant to penicillins, erythromycin, tetracycline, and ciprofloxacin. Analysis of the PB32 genome demonstrated that this strain was also related to a human MRSA strain. While PB32 was not a MRSA, a section of chromosomal DNA from PB32 genome did harbor a unique remnant of the methicillin resistance mobile element as well as a novel bovine staphylococcal pathogenicity island. This work demonstrates the dissemination of human S. aureus strains in cattle and reveals changes to the genome structure of human MRSA that might have been influenced by the introduction and dissemination of these strains in cattle populations.

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