Florfenicol susceptibility survey of EU field isolates of Actinobacillus pleuropneumoniae, Haemophilus parasuis and Pasteurella multocida

Florfenicol is a well recognized, broad spectrum antimicrobial with a high lipophilicity resulting in fast, significant serum concentrations and very good tissue distribution. Oral administration leads to an almost complete absorption of the molecule. Amphen® 200 mg/ g oral granules is a patented formulation containing 200 mg/ g florfenicol for use in drinking water of pigs. In this study, the florfenicol susceptibility of EU field isolates of 3 major swine bacterial pathogens was tested.

Susceptibility testing was carried out in a fully Good Laboratory Practice compliant study in one central laboratory. All tests were in accordance with the procedures of the Clinical and Laboratory Standards Institute. 222 Strains of bacterial pathogens from cases of porcine respiratory infections were collected in 7 European countries over the period 2008 - 2010. Representative strains of A. pleuropneumoniae (n=67), H. parasuis (n=54) and P. multocida (n=101) were tested in this large scale study. The MIC90 value (Minimal Inhibitory Concentration) for a specific bacteria is defined as the lowest concentration of an antimicrobial to inhibit growth of 90 % of the bacterial strains in vitro.

In this survey the MIC ranges for A. pleuropneumoniae, H. parasuis and P. multocida were respectively 0.06 - 1.0 μg/ ml, ≤0.015 - 1 μg/ ml and 0.25 - 1 μg/ ml with a very tight MIC distribution. The florfenicol MIC90 value for all three pathogens was determined at 0.5 μg/ ml and far below the clinical breakpoints (for A. pleuropneumoniae and P. multocida : susceptible ≤ 2 μg/ ml and resistant ≥ 8 μg/ ml). In comparison with different elaborate studies over the last 15 years, no changes in MIC data were noticed.

MIC values of florfenicol for three major swine respiratory pathogens are very favorable and do not seem to change over time. This confirms reports about the efficacy of the molecule in the field. The main hurdle for in water application was the absence of a practical water soluble florfenicol. The innovative formulation of Amphen® 200 mg/ g for use in bulk tanks and proportioners ensures a high success rate.

Disclosure of Interest: None Declared.