Thirty-eight Aerococcus viridans isolates were obtained from milk from 478 cows with clinical
mastitis in a farm during the periods between November 2011 and February 2012, and between December 2012 and March 2013. Additional isolates were obtained from processed
manure (a mixture of composted
manure, straw and hydrated
lime) and bedding materials. The processed
manure was later used to cover the floor of the stalls in barns as bedding materials. The temperatures recorded in the composted and processed
manure were not as high as those generally observed during satisfactory composting. To reveal the association of A. viridans in
manure-related products with intramammary
infection in cows, isolates were characterized by their
DNA fragment patterns as determined by pulsed-field gel electrophoresis (PFGE) and antimicrobial susceptibility testing. Isolates obtained from milk, processed
manure and bedding materials had identical
DNA fragment patterns. Antimicrobial susceptibilities were determined for 29 isolates from milk, processed
manure and bedding materials. Of these, 26 (89.7%) were resistant to
clindamycin, whereas virtually all the isolates were susceptible to 12 other antimicrobials including cefalosporins that have been used to treat
bovine mastitis in Japan. In vitro, three A. viridans isolates from milk and an isolate from processed
manure survived for 3 hr in Good's
buffer (pH 9) at high temperature (50°C). The results suggest that the processed
manure and bedding materials in this farm were possible sources of A. viridans that caused
infection in the cows with
mastitis.