Bacterial Susceptibility
Confirmation of a pathogen's susceptibility to an antimicrobial is essential to achieve the right therapeutic approach.
The Minimal Inhibitory Concentration (MIC) has been established as a standard for comparing the susceptibility of bacteria in vitro.
The unit is µg/ml and is given as MIC50 or MIC90 (indicating that the relevant concentration inhibits the growth of 50% or 90% of the bacteria of the tested population).
Results obtained from susceptibility testing (MIC tests and agar diffusion tests)always need careful interpretation. Contrary to these tests, which are performed under standardized conditions, nothing is static or standardized in the in vivo environment from which the pathogen was isolated. MICs and susceptibility follow their own dynamics and change over time. Bacterial isolates of a species may display different MICs even within a single animal or a group of animals. Despite these facts, the use of an antimicrobial classified as susceptible in in vitro testing has a high probability of successful therapy, whereas use of antimicrobial agents classified as resistant predicts a poor or no clinical response.
MIC values are particularly helpful when compared to the concentrations that a drug can achieve at the site of infection, in order to demonstrate the possibilities of successful therapy.
The high efficacy of Baytril becomes evident when comparing Enrofloxacin's MIC values for different pathogens with the achievable tissue concentrations and pharmacokinetic data.
