Isolation of Staphylococcus microti from milk of dairy cows with mastitis

• Our report describes the first case of bovine mastitis caused by Staphylococcus microti.
• Eleven isolates of S. microti shared the same genetic and biochemical properties.
• S. microti was able to cause intramammary infection in multiple cows in a dairy herd over a long period of time, thus indicating potential of contagious spread and some level of adaptation to the mammary gland.

The present paper is a case-report of multiple udder infections in a dairy herd caused by Staphylococcus microti. Over a 22-month period, eleven S. microti isolates from milk samples from 9 cows were collected. The animals experienced subclinical (with one exception) intramammary infections with a high self-cure rate. The identification of the microorganism was carried out by means of two independent approaches: nucleotide sequence analysis of the 16S rRNA gene, as well as some housekeeping genes (sodA, rpoB, dnaJ), and matrix-assisted laser desorption ionization—time of flight mass spectrometry. All S. microti isolates belonged to an apparently single clone (as detected by the RAPD analysis), indicating that the microorganism could adapt, to some degree, to the bovine mammary gland or even spread from cow to cow in a contagious manner. This report is, to our knowledge, the first ever case of bovine mastitis caused by S. microti and the first instance of isolation of this microorganism from domesticated animals.