Identification of Streptococcus spp. isolated from bovine milk and characterization of their antimicrobial susceptibility profiles in Taiwan

Abstract

Bovine mastitis has had a great impact on the economic losses of the dairy industry. Nowadays, environmental
pathogens cause the main types of bovine mastitis, especially the streptococci. The aim of the study was to identify the
major Streptococcus species causing bovine mastitis in Taiwan as well as to reveal their antimicrobial susceptibility
profiles. By colony morphology identifying, Gram staining, and subculturing on Edwards agar, the preliminary
identified streptococci were subjected to biochemical identification, latex agglutination tests and dick diffusion tests for
susceptibility tests of 16 antimicrobial agents. Among a total of 157 strains, Streptococcus uberis was the most dominant
species found, followed by S. bovis, S. dysgalactiae, S. agalactiae, S. equinus and S. mitis. Most of them were sensitive to
all the β-lactams we selected in the study, including amoxicillin, cefuroxime, cefazolin, bacitracin, ceftiofur, cloxacillin,
penicillin and ampicicllin. However, high resistant rates were observed to aminoglycosides, tetracyclines and
lincomycin. S. uberis was the main environmental mastitis causative pathogens in the present study. Beta-lactams were
the effective antimicrobials agents against them.