In vitro susceptibility of ceftiofur against Streptococcus equi subsp zooepidemicus and subsp equi isolated from horses with lower respiratory disease in Europe since 2002.

The research examined the effectiveness of an antibiotic, ceftiofur, and other antimicrobial agents against two sub-types of Streptococcus equi, a bacteria infecting horses’ respiratory systems. The study found ceftiofur to be quite effective, with a low concentration needed to inhibit 90% of the bacterial growth.

Research Methodology

• The researchers investigated in vitro (in a controlled lab environment) the performance of ceftiofur and six other antimicrobial agents against 79 isolates of Streptococcus equi subsp zooepidemicus. This bacterium was collected from horses experiencing respiratory issues in Europe during 2007 to 2008.
• The same in vitro testing of the drugs was applied against two distinct sub-groups of Streptococcus equi collected between 2002 to 2006. These included 59 samples of S. equi subsp zooepidemicus and 49 samples of S. equi subsp equi. The isolates were provided by veterinary diagnostic laboratories from across Europe.

Results

• The results showed a low concentration of ceftiofur (0.12 microg/ml) was sufficient to arrest the growth of 90% of the bacterial isolates. This measurement, known as the MIC90 (Minimum Inhibitory Concentration), reflects the lowest concentration at which a drug is able to inhibit bacterial growth.
• This concentration is well within the ‘susceptible’ breakpoint defined by the Clinical Laboratory Standards Institute (≤ 0.25 microg/ml) for ceftiofur against S. equi subsp zooepidemicus. In other words, the bacterium is very susceptible to the administered ceftiofur within this concentration range.
• The MIC90 values were consistent, holding true for samples collected from different sources, i.e., the diagnostic laboratories as well as the field study.

Conclusion

• The study’s findings demonstrated the effectiveness of ceftiofur in combating two sub-types of Streptococcus equi bacteria that contribute to respiratory diseases in horses.
• This kind of research contributes to the broader understanding of equine health and informs veterinarian practices when treating these types of infections.