Highly presumptive identification of bacterial isolates associated with the recent Canada-wide mastitis epizootic as Nocardia farcinica

Abstract

A highly presumptive identification of Nocardia farcinica was made of 47 bacterial isolates. Fifteen isolates from Alberta, 9 from Ontario, and 2 each from New Brunswick, Newfoundland, and Nova Scotia were from clinical cases involved in the Canadian mastitis epizootic. Seventeen additional isolates from Alberta were recovered from farm milk bulk tanks from herds found to have cows involved in the epizootic. All isolates were shown by high-performance liquid chromatography to possess mycolic acids of a size consistent with the genus Nocardia. All isolates were resistant to a concentration of 5 micrograms/mL of mitomycin C. Forty-five isolates grew well and 2 showed reduced growth in the presence of 50 micrograms/mL of kanamycin acid sulfate. Forty-six isolates were resistant to 5-fluorouracil at a concentration of 20 micrograms/mL. All isolates were resistant to lysozyme. Resistance to these compounds supported the placement of the isolates in the genus Nocardia. Thirty-five isolates produced strong beta-galactosidase reactions and 12 showed weak reactions. The demonstration of beta-galactosidase activity further supports the identification of the isolates as nocardiae. Attempts to identify the bacteria to species by high-performance liquid chromatography of mycolic acid esters were frustrated, since two species of Nocardia were found to have indistinguishable mycolic acid patterns. The physiological and growth characteristics of the isolates were consistent with Nocardia farcinica.