Prevalence and antimicrobial susceptibility of gram-negative bacteria isolated from bovine mastitis between 2003 and 2008 in Korea.

The objective of this study was to assess trends in the prevalence and distribution of gram-negative bacteria isolated from bovine mastitis and their antimicrobial susceptibilities during a 6-yr period between 2003 and 2008 in Korea. Escherichia coli, Pseudomonas fluorescens, Klebsiella pneumoniae, Enterobacter cloacae, Acinetobacter lwoffi/junii, Pseudomonas aeruginosa, and Serratia marcescens were the most commonly observed pathogens during this period. Generally, gram-negative bacteria showed low susceptibilities to most of the antimicrobials tested in this study, except amikacin and gentamicin. Although these 2 aminoglycosides were broadly active against gram-negative bacteria, less than half of those bacteria showed susceptibilities to streptomycin. The beta-lactams, except piperacillin, had the lowest activity among antimicrobials tested in this study. Susceptibilities to chloramphenicol and trimethoprim were fairy high in all genera of gram-negative bacteria, except Acinetobacter spp. and Pseudomonas spp., whereas relatively high resistance to tetracycline was observed uniformly among gram-negative bacteria. There was no significant change in the prevalence of bacterial and the proportion of antimicrobial resistance among gram-negative bacteria isolates during a 6-yr period.