Ceftiofur susceptibility of Streptococcus equi subsp zooepidemicus isolated from horses in North America between 1989 and 2008.

The article presents research about the effectiveness of the antibiotic ceftiofur on Streptococcus equi bacteria, a cause of respiratory infections in horses. The study finds that the bacteria’s susceptibility to this drug has stayed consistent over a two-decade span.

Research Methodology

• The study focuses on the in vitro activity of ceftiofur and six other antimicrobials.
• The antibiotics were tested against 516 Streptococcus equi subsp. zooepidemicus samples. These were gathered from horses suffering from respiratory infections in North America in 2007 and 2008.
• An additional 239 similar bacterial isolates were tested, collected between 1989 and 2007 from US and Canadian vet diagnostic labs.

Key Findings

• The lowest concentration of ceftiofur that stopped 90% of the bacterial growth (MIC90) was identified as 0.12 micrograms/ml for both groups of samples.
• The Clinical and Laboratory Standards Institute sets a susceptible breakpoint for ceftiofur against this bacterium. This is a minimum inhibitory concentration (MIC) value of ≤ 0.25 micrograms/ml.
• Importantly, the MIC90 values for both sets of isolates remained steady throughout the collection period of 19 years. This suggests the bacteria’s sensitivity to ceftiofur hasn’t evolved or decreased over time.

Implications

• The results of this study highlight the ongoing effectiveness of ceftiofur in treating lower respiratory tract infections in horses caused by S. equi bacteria. This can inform treatment strategies for such instances.
• Furthermore, the consistent MIC90 values over approximately two decades imply that resistance to the antimicrobial hasn’t developed significantly within the Streptococcus equi subsp. zooepidemicus bacteria. This lessens concerns of antibiotic resistance in this context.